1. Database Systems - Introduction to Databases and Data Warehouses
CHAPTER 5 - SQL

2. INTRODUCTION SQL - Structured Query Language SQL is used for:
Creating databases
Adding, modifying and deleting database structures
Inserting, deleting, and modifying records in databases
Querying databases (data retrieval)
SQL functions as a standard relational database language
It can be used (with minor dialectical variations) with the majority of relational DBMS software tools
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3. INTRODUCTION SQL commands – categories: Data Definition Language (DDL)
Data Manipulation Language (DML)
Data Control Language (DCL)
Transaction Control Language (TCL)
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4. INTRODUCTION Data Definition Language (DDL)
Used to create and modify the structure of the database
Example commands:
CREATE
ALTER
DROP
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5. INTRODUCTION Data Manipulation Language (DML)
Used to insert, modify, delete and retrieve data
Example commands:
INSERT INTO
UPDATE
DELETE
SELECT
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6. INTRODUCTION Data Control Language (DCL)
Used for data access control
Transaction Control Language (TCL)
Used for managing database transactions
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7. INTRODUCTION SQL data types
Each column of each SQL created relation has a specified data type
Commonly used SQL data types:
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8. INTRODUCTION Brief SQL syntax notes
Semicolon “;” following the end of an SQL statement, indicates the end of the SQL command
In a list of multiple SQL statements the semicolon indicates where each SQL statement ends
SQL keywords, as well as the table and column names used in the SQL commands, are not case sensitive
E.g. SELECT is the same as select or SeLeCt
An SQL statement can be written as one long sentence in one line of text
However, for legibility reasons SQL statements are usually broken down into multiple lines of text
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9. CREATE TABLE CREATE TABLE
Used for creating and connecting relational tables
DCL and TCL statements are covered in Chapter 10.
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10. ER diagram : ZAGI Retail Company Sales Department Database
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11. Relational schema: ZAGI Retail Company Sales Department Database
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12. CREATE TABLE statements for ZAGI Retail Company Sales Department Database
CREATE TABLE vendor
( vendorid CHAR(2) NOT NULL,
vendorname VARCHAR(25) NOT NULL,
PRIMARY KEY (vendorid) );
CREATE TABLE category
( categoryid CHAR(2) NOT NULL,
categoryname VARCHAR(25) NOT NULL,
PRIMARY KEY (categoryid) );
CREATE TABLE product
( productid CHAR(3) NOT NULL,
productname VARCHAR(25) NOT NULL,
productprice NUMERIC(7,2) NOT NULL,
vendorid CHAR(2) NOT NULL,
categoryid CHAR(2) NOT NULL,
PRIMARY KEY (productid),
FOREIGN KEY (vendorid) REFERENCES vendor(vendorid),
FOREIGN KEY (categoryid) REFERENCES category(categoryid) );
CREATE TABLE region
( regionid CHAR(1) NOT NULL,
regionname VARCHAR(25) NOT NULL,
PRIMARY KEY (regionid) );
This example is discussed on Page 70.
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13. CREATE TABLE statements for ZAGI Retail Company Sales Department Database
CREATE TABLE store
( storeid VARCHAR(3) NOT NULL,
storezip CHAR(5) NOT NULL,
regionid CHAR(1) NOT NULL,
PRIMARY KEY (storeid),
FOREIGN KEY (regionid) REFERENCES region(regionid) );
CREATE TABLE customer
( customerid CHAR(7) NOT NULL,
customername VARCHAR(15) NOT NULL,
customerzip CHAR(5) NOT NULL,
PRIMARY KEY (customerid) );
CREATE TABLE salestransaction
( tid VARCHAR(8) NOT NULL,
customerid CHAR(7) NOT NULL,
storeid VARCHAR(3) NOT NULL,
tdate DATE NOT NULL,
PRIMARY KEY (tid),
FOREIGN KEY (customerid) REFERENCES customer(customerid),
FOREIGN KEY (storeid) REFERENCES store(storeid) );
CREATE TABLE soldvia
( productid CHAR(3) NOT NULL,
tid VARCHAR(8) NOT NULL,
noofitems INT NOT NULL,
PRIMARY KEY (productid, tid),
FOREIGN KEY (productid) REFERENCES product(productid),
FOREIGN KEY (tid) REFERENCES salestransaction(tid) );
This example is discussed on Page 70.
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14. DROP TABLE DROP TABLE Used to remove a table from the database
This example is discussed on Page 70.
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15. Cannot delete a parent entity
DROP TABLE statements for ZAGI Retail Company Sales Department Database
INVALID SEQUENCE
DROP TABLE region;
DROP TABLE store;
DROP TABLE salestransaction;
DROP TABLE product;
DROP TABLE vendor;
DROP TABLE category;
DROP TABLE customer;
DROP TABLE soldvia;
Cannot delete a parent entity
This example is discussed on Pages
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16. DROP TABLE statements for ZAGI Retail Company Sales Department Database
INVALID SEQUENCE
DROP TABLE region;
DROP TABLE store;
DROP TABLE salestransaction;
DROP TABLE product;
DROP TABLE vendor;
DROP TABLE category;
DROP TABLE customer;
DROP TABLE soldvia;
VALID SEQUENCE
DROP TABLE soldvia;
DROP TABLE product;
DROP TABLE salestransaction;
DROP TABLE customer;
DROP TABLE category;
DROP TABLE vendor;
DROP TABLE store;
DROP TABLE region;
This example is discussed on Pages
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17. INSERT INTO INSERT INTO
Used to populate the created relations with data
This example is discussed on Pages
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18. Data records: ZAGI Retail Company Sales Department Database
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19. INSERT INTO statements for ZAGI Retail Company Sales Department Database
INSERT INTO vendor VALUES ('PG','Pacifica Gear');
INSERT INTO vendor VALUES ('MK','Mountain King');
INSERT INTO category VALUES ('CP','Camping');
INSERT INTO category VALUES ('FW','Footwear');
INSERT INTO product VALUES ('1X1','Zzz Bag',100,'PG','CP');
INSERT INTO product VALUES ('2X2','Easy Boot',70,'MK','FW');
INSERT INTO product VALUES ('3X3','Cosy Sock',15,'MK','FW');
INSERT INTO product VALUES ('4X4','Dura Boot',90,'PG','FW');
INSERT INTO product VALUES ('5X5','Tiny Tent',150,'MK','CP');
INSERT INTO product VALUES ('6X6','Biggy Tent',250,'MK','CP');
INSERT INTO region VALUES ('C','Chicagoland');
INSERT INTO region VALUES ('T','Tristate');
INSERT INTO store VALUES ('S1','60600','C');
INSERT INTO store VALUES ('S2','60605','C');
INSERT INTO store VALUES ('S3','35400','T');
INSERT INTO customer VALUES (' ','Tina','60137');
INSERT INTO customer VALUES (' ','Tony','60611');
INSERT INTO customer VALUES (' ','Pam','35401');
This example is discussed on Pages
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20. INSERT INTO statements for ZAGI Retail Company Sales Department Database
INSERT INTO salestransaction VALUES ('T111',' ','S1','01/Jan/2013');
INSERT INTO salestransaction VALUES ('T222',' ','S2','01/Jan/2013');
INSERT INTO salestransaction VALUES ('T333',' ','S3','02/Jan/2013');
INSERT INTO salestransaction VALUES ('T444',' ','S3','02/Jan/2013');
INSERT INTO salestransaction VALUES ('T555',' ','S3','02/Jan/2013');
INSERT INTO soldvia VALUES ('1X1','T111',1);
INSERT INTO soldvia VALUES ('2X2','T222',1);
INSERT INTO soldvia VALUES ('3X3','T333',5);
INSERT INTO soldvia VALUES ('1X1','T333',1);
INSERT INTO soldvia VALUES ('4X4','T444',1);
INSERT INTO soldvia VALUES ('2X2','T444',2);
INSERT INTO soldvia VALUES ('4X4','T555',4);
INSERT INTO soldvia VALUES ('5X5','T555',2);
INSERT INTO soldvia VALUES ('6X6','T555',1);
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21. SELECT
SELECT
Used for the retrieval of data from the database relations
Most commonly issued SQL statement
Basic form:
SELECT <columns>
FROM <table>
This example is discussed on Pages
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22. SELECT
Query 1 text: Retrieve the entire contents of the relation PRODUCT
Query 1: SELECT productid, productname, productprice, vendorid, categoryid FROM product;
Query 1 result:
This example is discussed on Pages
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23. SELECT
Query 1 text: Retrieve the entire contents of the relation PRODUCT
Query 1a: SELECT * FROM product;
Query 1a result:
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24. SELECT
Query 2 text: Retrieve the entire contents of the relation PRODUCT and show the columns in the following order: ProductName, ProductID, VendorID, CategoryID, ProductPrice
Query 2: SELECT productname, productid, vendorid, categoryid, productprice FROM product;
Query 2 result:
This example is discussed on Page 134.
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25. SELECT
Query 3 text: For the relation PRODUCT, show the columns ProductID and ProductPrice
Query 3: SELECT productid, productprice FROM product;
Query 3 result:
This example is discussed on Page 135.
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26. SELECT
SELECT
In addition to displaying columns, the SELECT clause can be used to display derived attributes (calculated columns) represented as expressions
SELECT statement can be structured as follows:
SELECT <columns, expressions> FROM <table>
This example is discussed on Page 135.
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27. SELECT
Query 3a text: For the relation PRODUCT, show the columns ProductID and ProductPrice
Query 3a: SELECT productid, productprice, productprice * FROM product;
Query 3a result:
This example is discussed on Page 135.
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28. SELECT
SELECT
The SELECT FROM statement can contain other optional keywords, such as WHERE, GROUP BY, HAVING, and ORDER BY, appearing in this order: :
SELECT <columns, expressions>
FROM <tables>
WHERE <row selection condition>
GROUP BY <grouping columns>
HAVING <group selection condition>
ORDER BY <sorting columns, expressions>
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29. WHERE
WHERE
WHERE condition determines which rows should be retrieved and consequently which rows should not be retrieved
The logical condition determining which records to retrieve can use one of the following logical comparison operators:
= Equal to < Less than > Greater than <= Less than or equal to >= Greater than or equal to != Not equal to <> Not equal to (alternative notation | uncommon)
This example is discussed on Page 136.
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30. WHERE
Query 4 text: Retrieve the product id, product name, vendor id, and product price for each product whose price is above $100
Query 4: SELECT productid, productname, vendorid, productprice FROM
product WHERE
productprice > 100;
Query 4 result:
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31. WHERE
Query 5 text: Retrieve the product id, product name, vendor id, and product price for each product in the FW category whose price is equal to or below $110
Query 5: SELECT
productid, productname, vendorid, productprice FROM
product WHERE
productprice <= 110
AND categoryid = 'FW';
Query 5 result:
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32. DISTINCT DISTINCT Can be used in conjunction with the SELECT statement
Eliminates duplicate values from a query result
This example is discussed on Page 136.
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33. DISTINCT
Query 6 text: Retrieve the VendorID value for each record in the relation PRODUCT
Query 6: SELECT
vendorid FROM
product;
Query 6 result:
This example is discussed on Page 137.
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34. DISTINCT
Query 7 text: Show one instance of all the different VendorID values in the relation PRODUCT Query 7: SELECT DISTINCT vendorid FROM product;
Query 7 result:
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35. ORDER BY
ORDER BY
Used to sort the results of the query by one or more columns (or expressions)
This example is discussed on Page 137.
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36. ORDER BY
Query 8 text: Retrieve the product id, product name, category id, and product price for each product in the FW product category, sorted by product price Query 8: SELECT productid, productname, categoryid, productprice FROM product WHERE categoryid = 'FW' ORDER BY productprice;
Query 8 result:
This example is discussed on Page 137.
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37. ORDER BY
Query 9 text: Retrieve the product id, product name, category id, and product price for each product in the FW product category, sorted by product price in descending order Query 9: SELECT productid, productname, categoryid, productprice FROM product WHERE categoryid = 'FW' ORDER BY productprice DESC;
Query 9 result:
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38. ORDER BY
Query 10 text: Retrieve the product id, product name, category id, and product price for each product, sorted by category id and, within the same category id, by product price Query 10 : SELECT productid, productname, categoryid, productprice FROM product ORDER BY categoryid, productprice;
Query 10 result:
This example is discussed on Page 138.
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39. LIKE
LIKE
Used for retrieval of records whose values partially match a certain criteria
This example is discussed on Page 138.
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40. LIKE
Query 11 text: Retrieve the record for each product whose product name contains the phrase ’Boot’
Query 11 : SELECT * FROM product WHERE productname LIKE '%Boot%';
Query 11 result:
This example is discussed on Page 138.
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41. Like Operator - Patterns
DESCRIPTION
WHERE CustomerName LIKE 'a%'
Finds any values that start with "a"
WHERE CustomerName LIKE '%a'
Finds any values that end with "a"
WHERE CustomerName LIKE '%or%'
Finds any values that have "or" in any position
WHERE CustomerName LIKE '_r%'
Finds any values that have "r" in the second position
WHERE CustomerName LIKE 'a_%_%'
Finds any values that start with "a" and are at least 3 characters in length
WHERE ContactName LIKE 'a%o'
Finds any values that start with "a" and ends with "o"
Tip: You can also combine any number of conditions using AND or OR operators
Reference:

42. AGGREGATE FUNCTIONS Aggregate functions
For calculating and summarizing values in queries, SQL provides the following aggregate functions:
COUNT
SUM
AVG
MIN
MAX
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43. AGGREGATE FUNCTIONS
Query 12 text: Retrieve the average price of all products
Query 12 : SELECT AVG(productprice) FROM product;
Query 12 result:
This example is discussed on Page 139.
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44. AGGREGATE FUNCTIONS
Query 13 text: Show how many products we offer for sale
Query 13 : SELECT COUNT(*) FROM product;
Query 13 result:
Functions SUM and AVG operate on numeric values only.
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45. AGGREGATE FUNCTIONS
Query 14 text: Retrieve the number of vendors that supply our products
Query 14 : SELECT COUNT(DISTINCT vendorid) FROM product;
Query 14 result:
This example is discussed on Page 139.
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46. AGGREGATE FUNCTIONS
Query 15 text: Retrieve the number of products, average product price, lowest product price, and highest product price in the CP product category
Query 15 : SELECT COUNT(*), AVG(productprice), MIN(productprice), MAX(productprice) FROM product WHERE categoryid = 'CP';
Query 15 result:
This example is discussed on Page 139.
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47. GROUP BY
GROUP BY
Enables summarizations across the groups of related data within tables
The GROUP BY statement is often used with aggregate functions (COUNT, MAX, MIN, SUM, AVG) to group the result-set by one or more columns
This example is discussed on Page 140.
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48. Out source – Group By Examples
SELECT COUNT(CustomerID), Country FROM Customers GROUP BY Country;
This example is discussed on Page 140.
Reference: 48

49. Out source – Group By Examples
This example is discussed on Page 140.
Reference:
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50. Out source – Group By Examples
SELECT COUNT(CustomerID), Country FROM Customers GROUP BY Country ORDER BY COUNT(CustomerID) DESC;
This example is discussed on Page 140.
Reference:
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51. Out source – Group By Examples
This example is discussed on Page 140.
Reference:
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52. Out source – Group By Examples
SELECT COUNT(CustomerID) as counter, Country FROM Customers GROUP BY Country ORDER BY counter DESC;
This example is discussed on Page 140.
Reference:
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53. GROUP BY
Query 16 text: For each vendor, retrieve the vendor id, number of products supplied by the vendor, and average price of the products supplied by the vendor
Query 16 : SELECT vendorid, COUNT(*), AVG(productprice) FROM product GROUP BY vendorid;
Query 16 result:
This example is discussed on Page 140.
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54. Query 16 illustration 54 Jukić, Vrbsky, Nestorov – Database Systems
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55. GROUP BY
Query 16 text: For each vendor, retrieve the vendor id, number of products supplied by the vendor, and average price of the products supplied by the vendor
Query 16 : SELECT vendorid, COUNT(*), AVG(productprice) INVALID FROM product; ERROR MESSAGE RETURNED
This example is discussed on Pages
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56. GROUP BY
Query 17 text: For each vendor, retrieve the number of products supplied by the vendor and the average price of the products supplied by the vendor
Query 17 : SELECT COUNT(*), AVG(productprice) FROM product GROUP BY vendorid;
Query 17 result (vs. Query 16):
This example is discussed on Pages
Query 17 result
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57. GROUP BY
Query 18 text: For each vendor, retrieve the vendor id and the number of products with a product price of $100 or higher supplied by the vendor
Query 18 : SELECT vendorid, COUNT(*) FROM product WHERE productprice >= GROUP BY vendorid;
Query 18 result:
This example is discussed on Page 142.
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58. GROUP BY
Query 19 text: Consider the groups of products where each group contains the products that are from the same category supplied by the same vendor. For each such group, retrieve the vendor id, product category id, number of products in the group, and average price of the products in the group.
Query 19 : SELECT vendorid, categoryid, COUNT(*), AVG(productprice) FROM product GROUP BY vendorid, categoryid;
Query 19 result:
This example is discussed on Pages 142.
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59. GROUP BY
Query 20 text: For each product, retrieve the ProductID value and the total number of product items sold within all sales transactions.
Query 20 : SELECT productid, SUM(noofitems) FROM soldvia GROUP BY productid;
Query 20 result:
This example is discussed on Pages
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60. GROUP BY
Query 21 text: For each product, retrieve the ProductID value and the number of sales transactions in which the product was sold
Query 21: SELECT productid, COUNT(*) FROM soldvia GROUP BY productid;
Query 21 result:
This example is discussed on Page 143.
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61. SELECT TOP, LIMIT, or ROWNUM Clause
SQL Select Top
Is used to specify the number of records to return
Useful on large tables with thousands of records
Returning a large number of records can impact on performance
Note
Not all database systems support the SELECT TOP clause
MYSQL supports the LIMIT clause to select a limited number of records
Oracle uses ROWNUM
This example is discussed on Page 143. 61

62. SELECT LIMIT - MYSQL MySQL Syntax SELECT column_name(s) FROM
table_name
WHERE
condition
LIMIT
number;
SELECT *
FROM
Customers
LIMIT 3;
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63. LIMIT 3
This example is discussed on Page 143. 63

64. SQL BETWEEN Between Operator Syntax
It selects values within a given range
Values can be numbers, text, or dates
Syntax
SELECT column_name(s) FROM table_name WHERE column_name BETWEEN value1 AND value2;
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65. BETWEEN Example SELECT * FROM Products
WHERE Price BETWEEN 10 AND 20 LIMIT 3;
This example is discussed on Page 143. 65

66. NOT BETWEEN Example SELECT * FROM Products
WHERE Price NOT BETWEEN 10 AND 20 LIMIT 3;
This example is discussed on Page 143. 66

67. BETWEEN w\ IN Example SELECT * FROM Products
WHERE (Price BETWEEN 10 AND 20)
AND NOT CategoryID IN (1, 2, 3)
LIMIT 3;
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68. BETWEEN Dates Example SELECT * FROM Orders WHERE OrderDate
BETWEEN ' ' AND ' ’ limit 3;
This example is discussed on Page 143. 68

69. CONCAT - Concatenate SELECT
CustomerName, Address + ', ' + PostalCode + ' ' + City + ', ' + Country AS Address
FROM Customers;
MySQL
SELECT 
CustomerName, CONCAT(Address,', ',PostalCode, ', ',City,', ',Country) AS Address FROM Customers;
This example is discussed on Page 143. 69

70. HAVING
HAVING
Enables summarizations across groups of related data within tables
Determines which groups will be displayed in the result of a query and, consequently, which groups will not be displayed in the result of the query
A query that contains a HAVING clause must also contain a GROUP BY clause
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71. HAVING vs. Where
WHERE clause is used for filtering rows and it applies on each and every row, while HAVING clause is used to filter groups in SQL
Where clause introduces a condition on individual rows
Having clause introduces a condition on aggregations
i.e. results of selection where a single result, such as count, average, min, max, or sum, has been produced from multiple rows
As a rule of thumb, use WHERE before GROUP BY and HAVING after GROUP BY.
It is a rather primitive rule
but it is useful in more than 90% of the cases.
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72. HAVING
Query 22 text: Consider the groups of products where each group contains the products that are from the same category and supplied by the same vendor. For each such group that has more than one product, retrieve the vendor id, product category id, number of products in the group, and average price of the products in the group.
Query 22: SELECT vendorid, categoryid, COUNT(*), AVG(productprice) FROM product GROUP BY vendorid, categoryid HAVING COUNT(*) > 1;
Query 22 result:
This example is discussed on Pages
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73. HAVING
Query 23 text: Consider the groups of products where each group contains the products that are from the same category, supplied by the same vendor, and whose product price is $50 or higher. For each such group that has more than one product, retrieve the vendor id, product category id, number of products in the group, and average price of the products.
Query 23: SELECT vendorid, categoryid, COUNT(*), AVG(productprice) FROM product WHERE productprice >= GROUP BY vendorid, categoryid HAVING COUNT(*) > 1;
Query 23 result:
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74. HAVING
Query 24 text: For each product that has more than three items sold within all sales transactions, retrieve the ProductID value and the total number of product items sold within all sales transactions
Query 24: SELECT productid, SUM(noofitems) FROM soldvia GROUP BY productid HAVING SUM(noofitems) > 3;
Query 24 result:
This example is discussed on Page 144.
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75. HAVING
Query 25 text: For each product that was sold in more than one sales transaction, retrieve the ProductID value and the number of sales transactions in which the product was sold
Query 25: SELECT productid, COUNT(*) FROM soldvia GROUP BY productid HAVING COUNT(*) > 1;
Query 25 result:
This example is discussed on Pages
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76. HAVING
Query 26 text: For each product that has more than three items sold within all sales transactions, retrieve the ProductID value
Query 26: SELECT productid FROM soldvia GROUP BY productid HAVING SUM(noofitems) > 3;
Query 26 result:
This example is discussed on Page 145.
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77. HAVING
Query 27 text: For each product that was sold in more than one sales transaction, retrieve the ProductID value
Query 27: SELECT productid FROM soldvia GROUP BY productid HAVING COUNT(*) > 1;
Query 27 result:
This example is discussed on Page 145.
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78. NESTED QUERIES Nested Query A query that is used within another query
A nested query is also referred to as an inner query,
The query that uses the nested query is referred to as an outer query
This example is discussed on Page 146.
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79. NESTED QUERIES
Query 28 text: For each product whose product price is below the average price of all products, retrieve the product id, product name, and product price
Query 28: SELECT productid, productname, productprice FROM product WHERE productprice < ( SELECT AVG(productprice) FROM product);
Query 28 result:
This example is discussed on Page 146.
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80. NESTED QUERIES
Query 28 text: For each product whose product price is below the average price of all products, retrieve the product id, product name, and product price
Query 28: SELECT productid, productname, productprice INVALID FROM product WHERE productprice < AVG(productprice);
A query may contain another query (or queries).
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81. SQL IN Operator IN Operator Syntax
Used for comparison of a value with a set of values
It allows you to specify multiple values in a WHERE clause
Is a shorthand for multiple or conditions
Syntax
SELECT column_name(s) FROM table_name WHERE column_name IN (value1, value2, …, valueN);
SELECT column_name(s) FROM table_name WHERE column_name IN (SELECT STATEMENT);
This example is discussed on Page 143. 81

82. IN Operator SELECT * FROM Customers WHERE Country
IN (‘Germany’, ‘France’, ‘UK’);
This example is discussed on Page 143. 82

83. IN Operator – query result
SELECT *
FROM
Customers
WHERE
Country
IN (‘Germany’, ‘France’, ‘UK’)
LIMIT 3;
This example is discussed on Page 143. 83

84. NOT IN Operator SELECT * FROM Customers WHERE Country
NOT IN (‘Germany’, ‘France’, ‘UK’);
This example is discussed on Page 143. 84

85. IN Operator – query result
SELECT *
FROM
Customers
WHERE
Country
NOT IN (‘Germany’, ‘France’, ‘UK’)
LIMIT 3;
This example is discussed on Page 143. 85

86. IN Operator – inner query
SELECT * FROM Customers
WHERE Country IN (SELECT Country FROM Suppliers);
This example is discussed on Page 143. 86

87. IN – Additional Samples
Query 29 text: For each product that has more than three items sold within all sales transactions, retrieve the product id, product name, and product price
Query 29: SELECT productid, productname, productprice FROM product WHERE productid IN (SELECT productid FROM soldvia GROUP BY productid HAVING SUM(noofitems) > 3);
Query 29 result:
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88. IN – Additional Samples
Query 30 text: For each product whose items were sold in more than one sales transaction, retrieve the product id, product name and product price
Query 30 : SELECT productid, productname, productprice FROM product WHERE productid IN (SELECT productid FROM soldvia GROUP BY productid HAVING COUNT(*) > 1);
Query 30 result:
This example is discussed on Page
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89. Exercises/Demo
Write a query that returns all regions that have no stores
Write a query that returns all customers who have not bought anything
Write a query that returns all customers who have made purchases
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90. JOIN A join clause is used to combine rows from two or more tables
Based on a related column between them (PK/FK)
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91. Types of JOIN
Inner Join (default): returns records that have matching values in both tables
Left (Outer) Join: Return all records from the left table, and the matched records from the right table
Right (Outer) Join: Return all records from the right table, and the matched records from the left table
Full (Outer) Join:  Return all records when there is a match in either left or right table
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92. Types of JOIN
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93. Inner Join Syntas
The INNER JOIN keyword selects records that have matching values in both tables.
select regionname from store inner join region on region.regionid = store.regionid;
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94. Inner Join Syntax w/ Group By
select regionname, count(*) as number_of_stores from store inner join region on region.regionid = store.regionid group by regionname;
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95. Inner Join Syntax w/ Group By
select regionname, count(*) as number_of_stores from store inner join region on region.regionid = store.regionid group by regionname;
having
number_of_stores > 1
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96. LEFT JOIN
The left join keyword returns all records from the left table (table1), and the matched records from the right table (table2). The result is NULL from the right side, if there is no match
SELECT column_name(s) FROM table1 LEFT JOIN table2 ON table1.column_name = table2.column_name;
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97. RIGHT JOIN
The RIGHT JOIN keyword returns all records from the right table (table2), and the matched records from the left table (table1). The result is NULL from the left side, when there is no match.
SELECT column_name(s) FROM table1 RIGHT JOIN table2 ON table1.column_name = table2.column_name;
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98. FULL OUTTER JOIN
The FULL OUTER JOIN keyword return all records when there is a match in either left (table1) or right (table2) table records.
Note: FULL OUTER JOIN can potentially return very large result-sets!
SELECT column_name(s) FROM table1 FULL OUTER JOIN table2 ON table1.column_name = table2.column_name;
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99. DEMO

100. DEMO
DEMO

101. DEMO
Customer
City

102. DEMO - INNER JOIN
Customer City

103. DEMO - LEFT OUTER JOIN
Customer City

104. DEMO - RIGHT OUTER JOIN
Customer City

105. DEMO – FULL OUTER JOIN
Customer City

106. ENTITY/Relation ALIAS
An alternative and usually shorter name that can be used anywhere within a query instead of the full relation name
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107. ALIAS
Query 31 text: For each product, retrieve the product id, name of the product, name of the vendor of the product, and price of the product
Query 31: SELECT productid, productname, vendorname, productprice FROM product, vendor WHERE product.vendorid = vendor.vendorid;
Query 31 result:
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108. ALIAS
Query 31a text: For each product, retrieve the product id, name of the product, (same query) name of the vendor of the product, and price of the product
Query 31a: SELECT p.productid, p.productname, v.vendorname, p.productprice FROM product p, vendor v WHERE p.vendorid = v.vendorid;
Query 31a result: (same result)
Columns can also have aliases but their use is more restricted within a query.
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109. ALIAS
Query 31b text: For each product, retrieve the product id, name of the product, (same query) name of the vendor of the product, and price of the product
Query 31b: SELECT p.productid pid, p.productname pname, v.vendorname vname, p.productprice pprice FROM product p, vendor v WHERE p.vendorid = v.vendorid;
Query 31b result: (same result, different column names in the result)
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110. ALIAS
Query 31c text: For each product, retrieve the product id, name of the product, (same query) name of the vendor of the product, and price of the product
Query 31c: SELECT p.productid AS pid, p.productname AS pname, v.vendorname AS vname, p.productprice AS pprice FROM product p, vendor v WHERE p.vendorid = v.vendorid;
Query 31c result: (same result, as Query 31b)
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111. ALTER TABLE (DML) ALTER TABLE
Used to change the structure of the relation, once the relation is already created
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112. ALTER TABLE
Alter Statement 1: ALTER TABLE vendor ADD ( vendorphonenumber CHAR(11));
Alter Statement 2: ALTER TABLE vendor DROP ( vendorphonenumber);
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113. UPDATE UPDATE Used to modify the data stored in database relations 113
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114. UPDATE
Insert Statement 1: INSERT INTO product VALUES ('7×7','Airy Sock',1000,'MK','CP');
Update Statement 1: UPDATE product SET productprice = WHERE productid = '7×7';
Alter Statement 3: ALTER TABLE product ADD (discount NUMERIC(3,2) );
Update Statement 2: UPDATE product SET discount = 0.2;
Update Statement 3: UPDATE product SET discount = WHERE vendorid = 'MK';
Alter Statement 4: ALTER TABLE product DROP (discount);
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115. DELETE DELETE Used to delete the data stored in database relations
This example is discussed on Pages
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116. DELETE
Delete Statement 1: DELETE FROM product WHERE productid = '7×7';
This example is discussed on Page 154.
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117. VIEW
VIEW
Mechanism in SQL that allows the structure of a query to be saved in the RDBMS
Also known as a virtual table
View is not an actual table and does not have any data physically saved
Every time a view is invoked, it executes a query that retrieves the data from the actual tables
A view can be used in SELECT statements just like any other table from a database
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118. VIEW Create View Statement 1:
CREATE VIEW products_more_than_3_sold AS SELECT productid, productname, productprice FROM product WHERE productid IN (SELECT productid FROM soldvia GROUP BY productid AVING SUM(noofitems) > 3);
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119. VIEW
Query 29 text: For each product that has more than three items sold within all sales transactions, retrieve the product id, product name, and product price
Query 29: SELECT productid, productname, productprice FROM product WHERE productid IN (SELECT productid FROM soldvia GROUP BY productid HAVING SUM(noofitems) > 3);
Query 29 result:
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120. VIEW
Query 29a text: For each product that has more than three items sold within all (same query) sales transactions, retrieve the product id, product name, and product price
Query 29a: SELECT * FROM products_more_than_3_sold;
Query 29a result:
(same result)
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121. VIEW Create View Statement 2:
CREATE VIEW products_in_multiple_trnsc AS SELECT productid, productname, productprice FROM product WHERE productid IN (SELECT productid FROM soldvia GROUP BY productid HAVING COUNT(*) > 1);
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122. VIEW
Query 30 text: For each product whose items were sold in more than one sales transaction, retrieve the product name and product price
Query 30 : SELECT productid, productname, productprice FROM product WHERE productid IN (SELECT productid FROM soldvia GROUP BY productid HAVING COUNT(*) > 1);
Query 30 result:
This example is discussed on Pages
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123. VIEW
Query 30a text: For each product whose items were sold in more than one sales (same query) transaction, retrieve the product name and product price
Query 30a : SELECT * FROM products_in_multiple_trnsc;
Query 30a result:
(same result)
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124. VIEW Views will remain stored in the database such as tables
list all views in the database using the following:
SHOW FULL TABLES IN databse_name
WHERE TABLE_TYPE LIKE 'VIEW’;
Update a View:
CREATE OR REPLACE VIEW view_name AS SELECT column1, column2, ... FROM table_name WHERE condition;
Delete/Drop a view:
DROP VIEW view_name;
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125. SET OPERATORS Set operators
Standard set operators: union, intersection, and difference
Used to combine the results of two or more SELECT statements that are union compatible
Two sets of columns are union compatible if they contain the same number of columns, and if the data types of the columns in one set match the data types of the columns in the other set
The first column in one set has a compatible data type with the data type of the first column in the other set, the second column in one set has a compatible data type with the data type of the second column in the other set, and so on.
The set operators can combine results from SELECT statements querying relations, views, or other SELECT queries.
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126. SET OPERATORS
UNION
Used to combine the union compatible results of two SELECT statements by listing all rows from the result of the first SELECT statement and all rows from the result of the other SELECT statement
If two or more rows are identical only one of them is shown (duplicates are eliminated from the result)
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127. SET OPERATORS
Query 36 text: Retrieve the product id, product name, and product price for each product that has more than three items sold within all sales transactions or whose items were sold in more than one sales transaction
Query 36: SELECT * FROM products_more_than_3_sold UNION SELECT * FROM products_in_multiple_trnsc;
Query 36 result:
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128. SET OPERATORS INTERSECT
Used to combine the results of two SELECT statements that are union compatible by listing every row that appears in the result of both of the SELECT statements
This example is discussed on Page 155.
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129. SET OPERATORS
Query 37 text: Retrieve the product id, product name, and product price for each product that has more than three items sold within all sales transactions and whose items were sold in more than one sales transaction
Query 37: SELECT * FROM products_more_than_3_sold INTERSECT SELECT * FROM products_in_multiple_trnsc;
Query 37 result:
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130. SET OPERATORS MINUS (EXCEPT)
Used to combine the results of two SELECT statements that are union compatible by listing every row from the result of the first SELECT statement that does not appear in the result of the other SELECT statement
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131. SET OPERATORS
Query 38 text: Retrieve the product id, product name, and product price for each product that has more than three items sold within all sales transactions but whose items were not sold in more than one sales transaction
Query 38: SELECT * FROM products_more_than_3_sold MINUS SELECT * FROM products_in_multiple_trnsc;
Query 38 result:
This example is discussed on Pages
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132. IS NULL
IS NULL
Used in queries that contain comparisons with an empty value in a column of a record
This example is discussed on Pages
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133. IS NULL
Query 45 text: Retrieve records for all managers who do not have a bonus
Query 45: SELECT * FROM manager WHERE mbonus IS NULL;
Query 45 result:
Regular JOIN is also sometimes referred to as an INNER JOIN, to differentiate it from the OUTER JOIN.
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134. INSERTING FROM A QUERY Inserting from a query
A query retrieving the data from one relation can be used to populate another relation
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135. INSERTING FROM A QUERY
Create Table Statement 1: CREATE TABLE cleaningdenormalized ( buildingid CHAR(3) NOT NULL, aptno CHAR(5) NOT NULL, smemberid CHAR(4) NOT NULL, smembername VARCHAR(15) NOT NULL, PRIMARY KEY (buildingid, aptno, smemberid));
Insert Statement 2:
INSERT INTO cleaningdenormalized SELECT c.buildingid, c.aptno, s.smemberid, s.smembername FROM cleaning c, staffmember s WHERE c.smemberid = s.smemberid;
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136. CASE
The CASE statement goes through conditions and return a value when the first condition is met (like an IF-THEN-ELSE statement)
So, once a condition is true, it will stop reading and return the result. If no conditions are true, it returns the value in the ELSE clause
If there is no ELSE part and no conditions are true, it returns NULL
CASE     WHEN condition1 THEN result1     WHEN condition2 THEN result2     WHEN conditionN THEN resultN     ELSE result END;
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137. CASE
SELECT OrderID, Quantity, CASE     WHEN Quantity > 30 THEN "The quantity is greater than 30"     WHEN Quantity = 30 THEN "The quantity is 30"     ELSE "The quantity is under 30" END AS QuantityText FROM OrderDetails;
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138. CASE
SELECT OrderID, Quantity, CASE     WHEN Quantity > 30 THEN "The quantity is greater than 30"     WHEN Quantity = 30 THEN "The quantity is 30"     ELSE "The quantity is under 30" END AS QuantityText FROM OrderDetails;
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139. CASE
The following SQL will order the customers by City. However, if City is NULL, then order by Country:
SELECT CustomerName, City, Country FROM Customers
ORDER BY
(CASE
WHEN City IS NULL THEN Country
ELSE City
END);
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140. COMMENTS Single line comments start with -- Multi-line Comments
--Select all: SELECT * FROM Customers;
Multi-line Comments
/*Select all the columns of all the records in the Customers table:*/ SELECT * FROM Customers;
SELECT /* city, */ quantity from Customer;
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141. REFERENCE
W3Schools
Can be accessed via: [
141