1. Chapter 7 Introduction to Structured Query Language (SQL)
Database Systems: Design, Implementation, and Management Eighth Edition
Chapter 7
Introduction to Structured Query Language (SQL)

2. Database Systems, 8th Edition

3. SQL commands 1. Capitalized words denote the command syntax
2. Lowercase words denote values that must be supplied by the user.
3. Brackets enclose optional syntax.
4. Ellipses (...) indicate that the accompanying syntactic clause may be repeated as necessary.
5. Each SQL command ends with a semicolon (;)
Database Systems, 8th Edition

4. Creating the Database Two tasks must be completed: First task:
Create database structure
Create tables that will hold end-user data
First task:
RDBMS creates physical files that will hold database
Differs substantially from one RDBMS to another
Database Systems, 8th Edition

5. Steps of creating a database:
The command:
CREATE SCHEMA AUTHORIZATION {creator}
E.g.
CREATE SCHEMA AUTHORIZATION RAGHAD
Database Systems, 8th Edition

6. Creating Tables
1. Identify the appropriate data type including length if required for each attribute.
2. Identify those columns that should accept null values
3. Identify those columns that need to be unique,
4. Identify all primary key-foreign key mates
In the VENDOR table:
PRIMARY KEY (V_CODE)In the PRODUCT table
FOREIGN KEY (V_CODE) REFERENCES VENDOR ON UPDATE CASCADE
Database Systems, 8th Edition

7. Creating Tables ..continued
Besides the PRIMARY KEY and FOREIGN KEY constraints,jh the ANSI SQL standard defines the following constraints: (NOT NULL, UNIQUE, DEFAULT, CHECK)
6. Identify any columns for which domain specifications may be stated that are more constrained than those established by data type. CHECK is used as a column constraint it may be possible to establish validation rules for values to be inserted into the database.
Database Systems, 8th Edition

8. Creating Tables ..continued
5. Determine values to be inserted in any columns for which default value is desired. DEFAULT can be used to define a value that is automatically inserted when no value is inserted during data entry.
Database Systems, 8th Edition

9. Data Types
Data type selection is usually dictated by nature of data and by intended use
Supported data types:
Number(L,D), Integer, Smallint, Decimal(L,D)
Char(L), Varchar(L), Varchar2(L)
Date, Time, Timestamp
Real, Double, Float
Interval day to hour
Many other types
Database Systems, 8th Edition

10. Creating Table Structures
Use one line per column (attribute) definition
Use spaces to line up attribute characteristics and constraints
Table and attribute names are capitalized
NOT NULL specification
UNIQUE specification
Database Systems, 8th Edition

11. Creating Table Structures (continued)
Primary key attributes contain both a NOT NULL and a UNIQUE specification
RDBMS will automatically enforce referential integrity for foreign keys
Command sequence ends with semicolon
Database Systems, 8th Edition

12. SQL Constraints NOT NULL constraint UNIQUE constraint
Ensures that column does not accept nulls
UNIQUE constraint
Ensures that all values in column are unique
DEFAULT constraint
Assigns value to attribute when a new row is added to table
CHECK constraint
Validates data when attribute value is entered
Database Systems, 8th Edition

13. CREATE TABLE CUSTOMER ( CUS_CODE NUMBER PRIMARY KEY,
CUS_LNAME VARCHAR(15) NOT NULL,
CUS_FNAME VARCHAR(15) NOT NULL,
CUS_INITIAL CHAR(1),
CUS_AREACODE CHAR(3) DEFAULT ‘615’ NOT NULL CHECK(CUS_AREACODE IN (‘615’,’713’,’931’)),
CUS_PHONE CHAR(8) NOT NULL,
CUS_BALANCE NUMBER(9,2) DEFAULT 0.00,
CONSTRAINT_CUS UI1 UNIQUE (CUS_LNAME, CUS_FNAME));
Database Systems, 8th Edition

14. Another example of the CHECK constraint: CREATE TABLE INVOICE (
CREATE TABLE INVOICE (
INV_NUMBER NUMBER PRIMARY KEY,
CUS_CODE NUMBER NOT NULL REFERENCES CUSTOMER (CUS_CODE),
INV_DATE DATE DEFAULT SYSDATE NOT NULL,
CONSTRAINT INV_CK1 CHECK (INV_DATE > TO_DATE(’01-JAN-2008’,’DD MMM-YYYY’)));
Database Systems, 8th Edition

15. CREATE TABLE lets you define constraints in 2 different places:
When you create the column definition (column constraint)
When you use the CONSTRAINT keyword ( table constraint)
Database Systems, 8th Edition

16. Creating Tables ...continued
7. create the table and any desired indexes using the CREATE TABLE and CREATE INDEX statements.
a common practice is to create an index on any field that is used as a search key
to delete an index, use the DROP INDEX command: DROP INDEX indexname
Database Systems, 8th Edition

17. SQL Indexes
When primary key is declared, DBMS automatically creates unique index
Often need additional indexes
Using CREATE INDEX command, SQL indexes can be created on basis of any selected attribute
Composite index
Index based on two or more attributes
Often used to prevent data duplication
Database Systems, 8th Edition

18. SQL INDEXES
Many RDBMs, including Access, automatically create a unique index on the PK attributes(s) when you declare the PK.
A common practice is to create an index on any field that is used as a search key.
By default all indexes produce results that are listed in ascending order, but you can create an index that yields output in descending order.
CREATE [UNIQUE]INDEX indexname ON tablename(column1,[,column2])
e.g.
CREATE INDEX P_INDATEX ON PRODUCT(P_INDATE);
CREATE UNIQUE INDEX P_CODEX ON PRODUCT (P_CODE);
CREATE UNIQUE INDEX EMP_TESTDEX ON TEST(EMP_NUM, TEST_CODE, TEST_DATE); (each employee does 1 test on a given date)
prevents you from entering a duplicate P_CODE value, and if you do the error message “duplicate value in index.”
Database Systems, 8th Edition

19. SQL Indexes
If the index should be in a descending order then this should be used:
CREATE INDEX PROD_PRICEX ON PRODUCT(P_PRICE DESC);
 To delete an index, use the
DROP INDEX COMMAND
DROP INDEX indexname 
DROP INDEX PROD_PRICEX;
. After creating the tables and some indexes, you are ready to start entering data.
Database Systems, 8th Edition

20. Data Manipulation Commands
INSERT
SELECT
COMMIT
UPDATE
ROLLBACK
DELETE
Database Systems, 8th Edition

21. Adding Table Rows INSERT Used to enter data into table Syntax:
INSERT INTO tablename VALUES (value1, value2, ..., valuen)
INSERT INTO VENDOR VALUES (21225,’BRYSON, Inc.’,’Smithson’,’615’,’ ’,’TN’,’Y’);
INSERT INTO VENDOR
VALUES (21226,’Superloo, Inc.’,’Flushing’.’904’,’ ’,’FL’,’N’);
(To see the contents of the PRODUCT table, use the
SELECT * FROM PRODUCT; command.)
Database Systems, 8th Edition

22. Adding Table Rows (continued)
When entering values, notice that:
Row contents are entered between parentheses
Character and date values are entered between apostrophes
Numerical entries are not enclosed in apostrophes
Attribute entries are separated by commas
A value is required for each column
Use NULL for unknown values
Database Systems, 8th Edition

23. Inserting Rows with Null Attributes
INSERT INTO PRODUCT
VALUES (‘BRT-345’.’Titanium drill bit’,’18-Oct-07’,’75’,10,4.50, 0.06, NULL);
There might be occasions when more than one attribute is optional. Rather than declaring each attribute as NULL in the insert command, you can indicate just the attributes that have required values.
INSERT INTO PRODUCT (P_CODE, P_DESCRIPT) VALUES (‘BRT-345’,’Titanium drill bit’);
Database Systems, 8th Edition

24. Saving Table Changes
Changes made to table contents are not physically saved on disk until:
Database is closed
Program is closed
COMMIT command is used
Syntax:
COMMIT [WORK];
Will permanently save any changes made to any table in the database
( MS ACCESS doesn’t support the COMMIT command because it automatically changes after the execution of each SQL command.)
Database Systems, 8th Edition

25. Listing Table Rows SELECT
Used to list contents of table
Syntax:
SELECT columnlist
FROM tablename;
Columnlist represents one or more attributes, separated by commas
Asterisk can be used as wildcard character to list all attributes
Database Systems, 8th Edition

26. Listing Table Rows ...continued
SQL commands can be grouped together on a single line, but complex command sequences are best shown on separate lines, with space between the SQL command and the command’s components. That makes it easy to trace the SQL logic, and to make corrections
SELECT P_CODE, P_DESCRIPT, P_INDATE, P_QOH, P_MIN, P_PRICE, P_DISCOUNT, V_CODE
FROM PRODUCT;
Database Systems, 8th Edition

27. Updating Table Rows UPDATE
Modify data in a table
Syntax:
UPDATE tablename SET columnname = expression [, columnname = expression] [WHERE conditionlist];
If more than one attribute is to be updated in row, separate corrections with commas
Database Systems, 8th Edition

28. UPDATE PRODUCT
SET columnname = expression [, columnname = expression]
[WHERE conditionlist];
If you want to change P_INDATE from December 13, 2007, to January 18, 2008, in the second row of the PRODUCT table, use the primary key (13-Q2/P2) to locate the correct (second) row.
SET PINDATE = ’18-JAN-2008’
WHERE P_CODE = ’13-Q2/P2’;
If more than one attribute is to be updated in the row, separate the corrections with commas:
SET P_INDATE = ’18-JAN-2008’, P_PRICE =17.99, P_MIN = 10
WHERE P_CODE ’13-Q2/P2’;
( if the WHERE condition wasn’t specified, the values of the named attributes will change in all rows of the table specified)
Database Systems, 8th Edition

29. To confirm the correction(s)  use the SELECT command to check the PRODUCT table’s listings.
SELECT * FROM PRODUCT;
Database Systems, 8th Edition

30. Restoring Table Contents
ROLLBACK
Undoes changes since last COMMIT
Brings data back to pre-change values
Syntax:
ROLLBACK;
COMMIT and ROLLBACK only work with commands to add, modify, or delete table rows  it will undo only the results of the INSERT and UPDATE commands.
Database Systems, 8th Edition

31. Restoring..continued MS Access doesn’t support the ROLLBACK command
. Because MS commits each row automatically, doing a ROLLBACK afterward wouldn’t have undone anything.
Database Systems, 8th Edition

32. Deleting Table Rows DELETE WHERE condition is optional
Deletes a table row
Syntax:
DELETE FROM tablename [WHERE conditionlist ];
WHERE condition is optional
If WHERE condition is not specified, all rows from specified table will be deleted
Database Systems, 8th Edition

33. Deleting Rows .. continued
e.g.
DELETE FROM PRODUCT
WHERE P_CODE = ‘BRT-345’;
(the primary key value lets SQL find the exact record to be deleted.)
Database Systems, 8th Edition

34. Inserting Table Rows with a SELECT Subquery
Inserts multiple rows from another table (source)
Uses SELECT subquery
Subquery: query embedded (or nested) inside another query
Subquery executed first
Syntax:
INSERT INTO tablename SELECT columnlist FROM tablename;
Database Systems, 8th Edition

35. SELECT Queries
SELECT, coupled with appropriate search conditions, is an incredibly powerful tool that enables you to transform data into information.
Fine-tune SELECT command by adding restrictions to search criteria using:
Conditional restrictions
Arithmetic operators
Logical operators
Special operators
Database Systems, 8th Edition

36. Selecting Rows with Conditional Restrictions
Select partial table contents by placing restrictions on rows to be included in output
Add conditional restrictions to SELECT statement, using WHERE clause
Syntax:
SELECT columnlist FROM tablelist [ WHERE conditionlist ] ;
Database Systems, 8th Edition

37. COMPARISON OPERATORS (=, <, <=, >, >=,<> or !=)
SELECT columnlist
FROM tablelist
[WHERE conditionlist];
e.g.
SELECT P_DESCRIPT, P_INDATE, P_PRICE, V_CODE
FROM PRODUCT
WHERE V_CODE = 21344;
COMPARISON OPERATORS (=, <, <=, >, >=,<> or !=)
SELECT P_DESCRIPT, P_QOH, P_MIN, P_PRICE
WHERE P_PRICE <= 10;
Database Systems, 8th Edition

38. Using Comparison Operators on Character Attributes
SELECT P_CODE, P_DESCRIPT, P_QOH, P_MIN, P_PRICE
FROM PRODUCT
WHERE P_CODE < ‘155-QW1’;
. according to ASCII code value for the letter B is greater than the value of the letter A, if follows that A is less than B, it follows that A is less that B)
so  11-QER/31<1558-QW1
Database Systems, 8th Edition

39. Using Comparison Operators on Dates
SELECT P_DESCRIPT, P_QOH, P_MIN, P_PRICE, P_INDATE
FROM PRODUCT
WHERE P_INDATE >= ‘20-Jan-2008’;
Using Computed Columns and Column Aliases
SELECT P_DESCRIPT, P_QOH,P_PRICE, P_QOH*P_PRICE
FROM PRODUCT;
(SQL accepts any valid expressions (or formulas) in the computed columns.Access automatically adds and Expr label to all computed columns. (The first computed column would be labled Expr1; the second, Expr2; and so on). Oracle uses the actual formula text as the label for the computed column
Database Systems, 8th Edition

40. The SQL permits the use of aliases for any column in a SELECT statement
An alias is an alternative name given to a column or table in any SQL STATEMENT.
SELECT P_DESCRIPT, P_QOH,P_PRICE, P_QOH*P_PRICE AS TOTVALUE
FROM PRODUCT;
Database Systems, 8th Edition

41. You could also use a computed column, an alias, and date arithmetic in a single query
MS Access version:
SELECT P_CODE,P_INDATE, DATE() – 90 AS CUTDATE
FROM PRODUCT
WHERE P_INDATE <= DATE() – 90;
Oracle version:
SELECT P_CODE, P_INDATE, SYSDATE – AS CUTDATE
WHERE P_INDATE<= SYSDATE – 90;
Database Systems, 8th Edition

42. Do this one!
Suppose a manager wants a list of all products, the dates they were recieved, and the warranty expiration date (90 days from when the product was received). How would you generate that list?
Database Systems, 8th Edition

43. The command will be
SELECT P_CODE, P_INDATE, P_INDATE + 90 AS EXPDATE FROM PRODUCT;
Database Systems, 8th Edition

44. Arithmetic Operators: The Rule of Precedence
Perform operations within parentheses
Perform power operations
Perform multiplications and divisions
Perform additions and subtractions
Database Systems, 8th Edition

45. Rules of Presedence: E.g. 8+2*5 =8+10=18
Perform operations within parenthesis
Perform power operations
Perform multiplications and divisions
Perform additions and subtractions
E.g.
8+2*5 =8+10=18
(8+2)*5 = 10 *5 = 50 and so on
Database Systems, 8th Edition

46. Logical Operators: AND, OR, and NOT
Searching data involves multiple conditions
Logical operators: AND, OR, and NOT
Can be combined
Parentheses placed to enforce precedence order
Conditions in parentheses always executed first
Boolean algebra: mathematical field dedicated to use of logical operators
NOT negates result of conditional expression
Database Systems, 8th Edition

47. SELECT P_DESCRIPT, P_INDATE, P_PRICE, V_CODE
FROM PRODUCT
WHERE (P_PRICE < 50 AND
P_INDATE > ’15-JAN-2008’)
OR V_CODE = 24288;
note the use of parentheses to combine logical restrictions.
Conditions listed within parentheses are always executed first.
Database Systems, 8th Edition

48. The NOT logical operator is used to find the rows that do not match a certain condition.
e.g.
if you want to see a listing of all rows for which the vendor code is not 21344, use the command sequence:
SELECT *
FROM PRODUCT
WHERE NOT (V_CODE =21344);
note that the condition is enclosed in parentheses; that practice is optional, but it is highly recommended for clarity.
. The logical NOT can be combined with AND and OR
Database Systems, 8th Edition

49. Special Operators
BETWEEN: checks whether attribute value is within a range
IS NULL: checks whether attribute value is null
LIKE: checks whether attribute value matches given string pattern
IN: checks whether attribute value matches any value within a value list
EXISTS: checks if subquery returns any rows
Database Systems, 8th Edition

50. BETWEEN (ORACLE Users always specify the lower range first)
SELECT *
FROM PRODUCT
WHERE P_PRICE BETWEEN AND ;
(ORACLE Users always specify the lower range first)
If your DBMS does not support BETWEEN, you can use:
SELECT *
WHERE P_PRICE > AND P_PRICE <100.00
Database Systems, 8th Edition

51. IS NULL
(suppose you want to list all products that do not have a vendor assigned (V_CODE is null)
SELECT P_CODE, P_DESCRIPT, V_CODE
FROM PRODUCT
WHERE V_CODE IS NULL;
( we cannot just say where V_CODE = NULL because NULL is not a “value” the way a 0 or the blank space is, but instead a NULL is a special property of an attribute that represents precisely the absence of any value.)
Database Systems, 8th Edition

52. LIKE
Used to check whether an attribute value matches a given string pattern.
( Standard SQL allows you to use the percent sign (%) and (_) underscore wild characters to make matches when the entire string is not known.
% means any and all following or preceding characters are eligible.
‘J%’ includes Johnson, Jones, July and J-231Q.
‘JO % ‘ includes Johnson and Jones.
‘%n’ includes Johnson and Jernigan.
Means any one character may be substituted for the underscore
_ ’ includes , etc.
‘_o_es’ includes Jones, Cones, Cokes, totes, and roles.
Database Systems, 8th Edition

53. SELECT V_NAME , V_ CONTACT, V_AREACODE, V_PHONE FROM VENDOR
E.g.
SELECT V_NAME , V_ CONTACT, V_AREACODE, V_PHONE
FROM VENDOR
WHERE V_CONTACT LIKE ‘Smith%’;
If you want to avoid the case sensitivity then change the last line to
WHERE UPPER(V_CONTACT) LIKE ‘SMITH%’;
The preceding query produces a list including all rows that contain a last name that begins with Smith , regardless of uppercase or lowercase letter combinations such as Smith, smith, and SMITH.
(ORACLE case sensitive, MS Access is not)
Database Systems, 8th Edition

54. The logical operators may be used with the special operators
SELECT V_NAME , V_ CONTACT, V_AREACODE, V_PHONE
FROM VENDOR
WHERE V_CONTACT NOT LIKE ‘Smith%’;
We can combine wildcards
e.g. ‘_l%’ can yield the strings Al, Alton, Elgin, Blakeston, blank, bloated and eligible.
Database Systems, 8th Edition

55. IN Used to check whether an attribute value
matches any value within a value list.
Many queries that would require the use of the logical OR can be more easily handled with the help of the special operator IN.
e.g.
SELECT *
FROM PRODUCT
WHERE V_CODE = 21344
OR V_CODE = 24288;
Database Systems, 8th Edition

56. Can be handled more efficiently with
SELECT *
FROM PRODUCT
WHERE V_CODE IN (21344, 24288);
(all values in the list must be of the same data type)
The IN operator is especially valuable when used in conjunction with subqueries.
Suppose you want to list the V_CODE and V_NAME of only those vendors who provide products.
SELECT V_CODE, V_NAME
FROM VENDOR
WHERE V_CODE IN (SELECT V_CODE FROM PRODUCT);
Database Systems, 8th Edition

57. EXISTS special operator
Can be used whenever there is a requirement to execute a command based on the result of another query. That is, if a subquery returns any rows, run the main query; otherwise don’t.
E.g.
SELECT *
FROM VENDOR
WHERE EXISTS (SELECT * FROM PRODUCT WHERE P_QOH < P_MIN);
This will list all vendors, but only if there are products to order.
Database Systems, 8th Edition

58. Try to do this one!
The EXISTS special operator is used to list all vendors, but only if there are products with the quantity on hand, less than double the minimum quantity
Database Systems, 8th Edition

59. SELECT. FROM VENDOR WHERE EXISTS (SELECT
SELECT * FROM VENDOR WHERE EXISTS (SELECT * FROM PRODUCT WHERE P_QOH < P_MIN*2);
Database Systems, 8th Edition

60. Advanced Data Definition Commands
All changes in table structure are made by using ALTER command
Three options
ADD adds a column
MODIFY changes column characteristics
DROP deletes a column
Can also be used to:
Add table constraints
Remove table constraints
Database Systems, 8th Edition

61. Changing a Column’s Data Type
ALTER can be used to change data type
Some RDBMSs do not permit changes to data types unless column is empty
E.g.
ALTER TABLE PRODUCT
MODIFY (V_CODE CHAR(5));
Changes the number V_CODE in the PRODUCT table to a character V_CODE
Database Systems, 8th Edition

62. Changing a Column’s Data Characteristics
Use ALTER to change data characteristics
Changes in column’s characteristics permitted if changes do not alter the existing data type
E.g. If you want to increase the width of the P_PRICE column to 9 digits, use the command:
ALTER TABLE PRODUCT
MODIFY(P_PRICE DECIMAL(9,2));
If you list the table, you see that the column width has increased by one digit
Database Systems, 8th Edition

63. Adding a Column Use ALTER to add column
Do not include the NOT NULL clause for new column (at first it will be nulls!)
ALTER TABLE PRODUCT
ADD(P_SALECODE CHAR(1));
Database Systems, 8th Edition

64. Dropping a Column Use ALTER to drop column
Some RDBMSs impose restrictions on the deletion of an attribute
ALTER TABLE VENDOR
DROP COLUMN V_ORDER;
Some RDBMSs impose restrictions on attribute deletion. E.g. you may not drop attributes that are involved in foreign key relationships, nor may you delete an attribute of a table that contains only that one attribute.
Database Systems, 8th Edition

65. Advanced Data Updates
UPDATE command updates only data in existing rows
If relationship between entries and existing columns, can assign values to slots
Arithmetic operators useful in data updates
In Oracle, ROLLBACK command undoes changes made by last two UPDATE statements
Database Systems, 8th Edition

66. To enter the P_SALECODE value ‘1’ for P_CODE value in the 3rd row, use the UPDATE command together with the primary key P_CODE ‘154-QQ2’ UPDATE PRODUCT SET P_SALECODE = ‘1’ WHERE P_CODE = ‘154-QQ2’;
Database Systems, 8th Edition

67. If you want to enter the P_SALECODE value ‘2’ for the P_CODE values ‘2232/QWE’ and ‘2232/QTY’; UPDATE PRODUCT SET P_SALECODE = ‘2’ WHERE P_CODE IN (‘2232/QWE’,’ 2232/QTY’);
Database Systems, 8th Edition

68. Try this one
If you want to place sales codes based on P_INDATE into the table using the following schedule: P_INDATE P_SALECODE Before Dec Between Jan 16, 2008 and Feb 10,
Database Systems, 8th Edition

69. UPDATE PRODUCT SET P_SALECODE =‘2’ WHERE P_INDATE< ‘25-Dec-2007’; SET P_SALECODE= ‘1’ WHERE P_INDATE >=‘16-Jan-2008’ AND P_INDATE <= ‘10-Feb-2008’; To check the results of those commands: SELECT P_CODE, P_DESCRIPT, P_INDATE, P_PRICE, P_SALECODE FROM PRODUCT;
Database Systems, 8th Edition

70. Database Systems, 8th Edition

71. Copying Parts of Tables
SQL permits copying contents of selected table columns
Data need not be reentered manually into newly created table(s)
First create the table structure
Next add rows to new table using table rows from another table
Database Systems, 8th Edition

72. If you want to copy P_CODE, P_DESCRIPT, P_PRICE, and V_CODE from the PRODUCT table to a new table named PART, you create the PART table structure first:
CREATE TABLE PART(
PART_CODE CHAR(8) NOT NULL UNIQUE,
PART_DESCRIPT CHAR(35),
PART_PRICE DECIMAL(8,2),
V_CODE INTEGER,
PRIMARY KEY (PART_CODE));
Database Systems, 8th Edition

73. You need to add the rows to the new PART table, using the PRODUCT table rows. To do that you use the INSERT command:
INSERT INTO PART(PART_CODE, PART_DESCRIPT, PART_PRICE, V_CODE)
SELECT P_CODE, P_DESCRIPT, P_PRICE, V_CODE FROM PRODUCT;
Database Systems, 8th Edition

74. You can also create the PART table as follows:
CREATE TABLE PART AS
SELECT P_CODE AS PART_CODE, P_DESCRIPT AS PART DESCRIPT,P_PRICE AS PART_PRICE, V_CODE
FROM PRODUCT;
Database Systems, 8th Edition

75. Database Systems, 8th Edition

76. Adding Primary and Foreign Key Designations
When table is copied, integrity rules do not copy
Primary and foreign keys manually defined on new table
Use ALTER TABLE command
Syntax:
ALTER TABLE tablename ADD PRIMARY KEY(fieldname);
For foreign key, use FOREIGN KEY in place of PRIMARY KEY
Database Systems, 8th Edition

77. Adding Primary and Foreign Key Designations
ALTER TABLE PART
ADD FORIEGN KEY (V_CODE) REFERENCES VENDOR;
If neither the PART table’s primary key nor its foreign key has been designated.
ALTER TEBLE PART
ADD PRIMARY KEY (PART_CODE)
ADD FORIEGN KEY (V_CODE) REFERENCES VENDOR;
Database Systems, 8th Edition

78. Even composite primary keys and multiple foreign keys can be designated in a single SQL command
ALTER TABLE LINE ADD PRIMARY KEY(INV_NUMBER, LINE_NUMBER) ADD FOREIGN KEY (INV_NUMBER) REFERENCES INVOICE ADD FOREIGN KEY (PROD_CODE) REFERENCES PRODUCT;
Database Systems, 8th Edition

79. Deleting a Table from the Database
DROP
Deletes table from database
Syntax:
DROP TABLE PART;
Can drop a table only if it is not the “one” side of any relationship
Otherwise RDBMS generates an error message
Foreign key integrity violation
Database Systems, 8th Edition

80. Advanced SELECT Queries
Logical operators work well in the query environment
SQL provides useful functions that:
Count
Find minimum and maximum values
Calculate averages, etc.
SQL allows user to limit queries to:
Entries having no duplicates
Entries whose duplicates may be grouped
Database Systems, 8th Edition

81. Ordering a Listing
ORDER BY clause useful when listing order important to you.
Syntax:
SELECT columnlist
FROM tablelist
[WHERE conditionlist]
[ORDER BY columnlist [ASC | DESC]];
Ascending order by default
Database Systems, 8th Edition

82. Try to produce the list in descending order!
If you want the contents of the PRODUCT table listed by P_PRICE in ascending order, use:
SELECT P_CODE, P_DESCRIPT, P_INDATE, P_PRICE
FROM PRODUCT
ORDER BY P_PRICE;
Try to produce the list in descending order!
Database Systems, 8th Edition

83. It will be : SELECT P_CODE, P_DESCRIPT, P_INDATE, P_PRICE FROM PRODUCT
ORDER BY P_PRICE DESC;
Database Systems, 8th Edition

84. Cascading order sequence
Ordering listings are used frequently e.g. Phone directory. It would be helpful if you could produce an ordered sequence (last name, first name, initial) in 3 stages
ORDER BY last name.
Within the last names, ORDER BY first name.
Within the first and last names, ORDER BY middle initial.
Such a multilevel ordered sequence is known as a cascading order sequence
Database Systems, 8th Edition

85. ORDER BY with other SQL commands
Typically, invoice due dates are listed in descending order. Or the largest prices first.
SELECT P_DESCRIPT, V_CODE, P_INDATE, P_PRICE
FROM PRODUCT
WHERE P_INDATE <=‘21-Jan-2008’ AND
P_PRICE<= 50.00
ORDER BY V_CODE, P_PRICE DESC;
Database Systems, 8th Edition

86. Listing Unique Values
DISTINCT clause produces list of only values that are different from one another
Example:
SELECT DISTINCT V_CODE
FROM PRODUCT;
Access places nulls at the top of the list
Oracle places it at the bottom
Placement of nulls does not affect list contents
Database Systems, 8th Edition

87. Listing Unique Values
How many different vendors are currently represented in the PRODUCT table? A simple listing (SELECT) is not very useful if the table contains several thousand rows and you have to sift through the vendor codes manually. DISTINCT clause produces a list of only those values that are different from one another. SELECT DISTINCT V_CODE FROM PRODUCT; (Access places the null V_CODE at the top of the list, Oracle places it at the bottom)
Database Systems, 8th Edition

88. Aggregate Functions
COUNT function tallies number of non-null values of an attribute
Takes one parameter: usually a column name
MAX and MIN find highest (lowest) value in a table
Compute MAX value in inner query
Compare to each value returned by the query
SUM computes total sum for any specified attribute
AVG function format similar to MIN and MAX
Database Systems, 8th Edition

89. COUNT in conjunction with DISTINCT
You want to find out how many different vendors are in the PRODUCT table, not counting the null values. SELECT COUNT(DISTINCT V_CODE) FROM PRODUCT; Result: COUNT (DISTINCTV_CODE)
Database Systems, 8th Edition

90. SELECT COUNT(DISTINCT V_CODE) FROM PRODUCT WHERE P_PRICE <= 10
SELECT COUNT(DISTINCT V_CODE) FROM PRODUCT WHERE P_PRICE <= 10.00; Result: COUNT (DISTINCTV_CODE)
Database Systems, 8th Edition

91. SELECT COUNT (. ) FROM PRODUCT WHERE P_PRICE <= 10
SELECT COUNT (*) FROM PRODUCT WHERE P_PRICE <= COUNT (DISTINCTV_CODE)
Database Systems, 8th Edition

92. MAX and MIN Help you find the answers to problems such as:
Highest (maximum) price in the PRODUCT table
Lowest (minimum) price in the PRODUCT table.
SELECT P_CODE, P_DESCRIPT, P_PRICE
FROM PRODUCT
WHERE P_PRICE = MAX(P_PRICE);
This will not yield the expected results, because the use of MAX(P_PRICE)to the right side of a comparison operator is incorrect n

93. To answer the query you must compute the maximum price first then compare it to each price returned by the query
To do that you need a nested query.
In this case the nested query is composed of 2 parts.
The inner query, which is executed first
The outer query, which is executed last
(remember, the outer query is always the first SQL command you encounter- in this case SELECT)
Database Systems, 8th Edition

94. MAX in a nested query
SELECT P_CODE, P_DESCRIPT, P_PRICE FROM PRODUCT WHERE P_PRICE = (SELECT MAX(P_PRICE) FROM PRODUCT);
Database Systems, 8th Edition

95. SUM
SELECT SUM(CUS_BALANCE) AS TOTBALANCE FROM CUSTOMER; This computes the total amount owed by your customers.
Database Systems, 8th Edition

96. AVG Similar to MAX and MIN SELECT AVG(P_PRICE) FROM PRODUCT;
SELECT P_CODE, P_DESCRIPT, P_QOH, P_PRICE, V_CODE
FROM PRODUCT
WHERE P_PRICE> (SELECT AVG(P_PRICE) FROM PRODUCT)
ORDER BY P_PRICE DESC;
Database Systems, 8th Edition

97. Grouping Data Syntax: SELECT columnlist FROM tablelist
[WHERE conditionlist]
[GROUP BY columnlist]
[HAVING conditionlist]
[ORDER BY columnlist [ASC | DESC] ] ;
Database Systems, 8th Edition

98. GROUP BY
Frequency distributions can be created quickly and easily using the GROUP BY clause within the SELECT statement.
The GROUP BY clause is valid ONLY when used in conjunction with one of the SQL aggregate functions (COUNT, MIN, MAX, AVG and SUM)
Nulls are included within the grouping.
Database Systems, 8th Edition

99. Aggregate the total cost of products grouped by V_CODE
SELECT V_CODE, SUM(P_QOH * P_PRICE) AS TOTCOST
FROM PRODUCT
GROUP BY V_CODE
HAVING (SUM(P_QOH*P_PRICE) >500
ORDER BY SUM (P_QOH *P_PRICE) DESC;
THIS WILL
Aggregate the total cost of products grouped by V_CODE
Select only the rows having totals that exceed $500
List the results in descending order by the total cost
(note the syntax used in the HAVING and ORDER BY clauses; you must specify the column expression(formula) used in the SELECT statement’s columnlist, rather than the column alias (TOTCOST). Some RDBMSs allow you to substitute with the column alias, while others don’t f

100. A wrong use of GROUP BY
SELECT V_CODE, P_CODE, P_DESCRIPT, P_PRICE FROM PRODUCT GROUP BY V_CODE; It will generate an error message saying that it is not a GROUP BY expression.
Database Systems, 8th Edition

101. A correct use of GROUP BY
SELECT V_CODE, COUNT(DISTINCT(P_CODE))
FROM PRODUCT
GROUP BY V_CODE;
V_CODE COUNT(DISTINCT(P_CODE)) 2
Produces 4 rows with a row that has V_CODE with Null values.
Database Systems, 8th Edition

102. The GROUP BY feature’s HAVING clause
The HAVING operates very much like the WHERE clause in the SELECT statement.
However the WHERE clause applies to columns and expressions for individual rows, while :
the HAVING clause is applied to the output of a GROUP BY operation.
Database Systems, 8th Edition

103. When using the GROUP BY clause with a SELECT statement
The SELECT’s columnlist must include a combination of column names and aggregate functions.
The GROUP BY clauses columnlist must include all non aggregate function columns specified in the SELECT’s columnlist. If required, you could also group by any aggregate function columns that appear in the SELECT’s columnlist.
The GROUP By clause columnlist can include any columns from the tables in the FROM clause of the SELECT statement, even if they do not appear in the SELECT’s columnlist.
Database Systems, 8th Edition

104. SELECT V_CODE, COUNT(DISTINCT (P_CODE)), AVG(P_PRICE) FROM PRODUCT GROUP BY V_CODE; (GROUP BY with the aggregate function COUNT and AVG) FROM PRODUCT GROUP BY V_CODE HAVING AVG (P_PRICE) <10;
Database Systems, 8th Edition

105. Virtual Tables: Creating a View
View is virtual table based on SELECT query
Create view by using CREATE VIEW command
Special characteristics of relational view:
Name of view can be used anywhere a table name is expected
View dynamically updated
Restricts users to only specified columns and rows
Views may be used as basis for reports
Database Systems, 8th Edition

106. CREATING A VIEW
Suppose that at the end of every day, you would like to get a list of all products to reorder, that is, products with a quantity on hand that is less than or equal to the minimum quantity. Instead of typing the same query at the end of every day wouldn’t it be better to permanently save that query in the database? That’s the function of a relational view. SYNATAX : CREATE VIEW; CREATE VIEW viewname AS SELECT query
Database Systems, 8th Edition

107. Creating a virtual table with the CREATE VIEW command
CREATE VIEW PRICEGT50 AS SELECT P_DESCRIPT, P_QOH,P_PRICE FROM PRODUCT WHERE P_PRICE > 50.00;
Database Systems, 8th Edition

108. Joining Database Tables
Joining tables is the most important distinction between relational database and other DBs
Join is performed when data are retrieved from more than one table at a time
Equality comparison between foreign key and primary key of related tables
Join tables by listing tables in FROM clause of SELECT statement
Database Systems, 8th Edition

109. NATURAL JOIN
SELECT P_DESCRIPT,P_PRICE, V_NAME, V_CONTACT, V_AREACODE, V_CODE, V_PHONE FROM PRODUCT, VENDOR WHERE PRODUCT. V_CODE = VENDOR.V_CODE; The order of the columns is not relevant To generate a more predictable list by using ORDER BY clause SELECT P_DESCRIP,P_PRICE, V_NAME, V_CONTACT, V_AREACODE, V_CODE, V_PHONE ORDER BY P_PRICE (always from lowest price to highest price
Database Systems, 8th Edition

110. When joining 3 or more table, you need to specify a join condition for each pair of tables.
The number of join conditions will always be N-1, where N represents the number of tables listed in the FROM clause.
E.g.
3 tables  you have 2 conditions
5 tables  you must have four join conditions
And so on.
Database Systems, 8th Edition

111. SELECT CUS_LNAME, INV_NUMBER, INV_DATE, P_DESCRIPT FROM CUSTOMER, INVOICE, LINE, PRODUCT WHERE CUSTOMER.CUS_CODE=INVOICE.CUS_CODE AND INVOICE.INV_NUMBER=LINE.INV_NUMBER AND LINE.P_CODE=PRODUCT.P_CODE AND CUSTOMER.CUS_CODE= ORDER BY INV_NUMBER;
Database Systems, 8th Edition

112. Joining Tables with an Alias
Alias identifies the source table from which data are taken
Alias can be used to identify source table
Any legal table name can be used as alias
Add alias after table name in FROM clause
FROM tablename alias
Database Systems, 8th Edition

113. SELECT P_DESCRIPT, P_PRICE, V_NAME, V_CONTACT, V_AREACODE, V_PHONE FROM PRODUCT P, VENDOR V WHERE P.V_CODE = V.V_CODE ORDER BY P_PRICE; The aliases P and V are used to label the PRODUCT and VENDOR tables in the next command sequence.
Database Systems, 8th Edition

114. Recursive Joins Outer Joins
Alias especially useful when a table must be joined to itself
Recursive query
Use aliases to differentiate the table from itself
Two types of outer join
Left outer join
Right outer join
Database Systems, 8th Edition

115. Recursive JOIN
SELECT E.EMP_MGR, M.EMP_LNAME, E.EMP_NUM, E.EMP_LNAME FROM EMP E, EMP M WHERE E.EMP_MGR=M.EMP_NUM ORDER BY E.EMP_MGR To list the employees with their managers and ordered by the managers
Database Systems, 8th Edition

116. OUTER JOINS
SELECT P_CODE, VENDOR.V_CODE, V_NAME FROM VENDOR LEFT JOIN PRODUCT ON VENDOR. V_CODE = PRODUCT. V_CODE; ( this will show all the v_code from the VENDOR table with no null values and the nulls in the P_Code) SELECT P_CODE, VENDOR.V_CODE, V_NAME FROM VENDOR RIGHT JOIN PRODUCT ON VENDOR.V_CODE = PRODUCT.V_CODE; (this will show all the P_CODE without null values and the nulls in the V_CODE)
Database Systems, 8th Edition

117. Summary SQL commands can be divided into two overall categories:
Data definition language commands
Data manipulation language commands
The ANSI standard data types are supported by all RDBMS vendors in different ways
Basic data definition commands allow you to create tables, indexes, and views
Database Systems, 8th Edition

118. Summary (continued)
DML commands allow you to add, modify, and delete rows from tables
The basic DML commands:
SELECT, INSERT, UPDATE, DELETE, COMMIT, and ROLLBACK
SELECT statement is main data retrieval command in SQL
Database Systems, 8th Edition

119. Summary (continued)
WHERE clause can be used with SELECT, UPDATE, and DELETE statements
Aggregate functions
Special functions that perform arithmetic computations over a set of rows
ORDER BY clause
Used to sort output of SELECT statement
Can sort by one or more columns
Ascending or descending order
Database Systems, 8th Edition

120. Summary (continued)
Join output of multiple tables with SELECT statement
Join performed every time you specify two or more tables in FROM clause
If no join condition specified, DBMX performs Cartesian product
Natural join uses join condition to match only rows with equal values in specified columns
Right outer join and left outer join select rows with no matching values in other related table
Database Systems, 8th Edition