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

Introduction to SQL SQL functions fit into two broad categories: Data definition language Data manipulation language Basic command set has vocabulary of fewer than 100 words American National Standards Institute (ANSI) prescribes a standard SQL Several SQL dialects exist Database Systems, 10th Edition

Database Systems, 10th Edition

Database Systems, 10th Edition

Data Definition Commands The database model In this chapter, a simple database with these tables is used to illustrate commands: CUSTOMER INVOICE LINE PRODUCT VENDOR Focus on PRODUCT and VENDOR tables Database Systems, 10th Edition

Database Systems, 10th Edition

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, 10th Edition

Creating the Database (cont’d.) Authentication DBMS verifies that only registered users are able to access database Log on to RDBMS using user ID and password created by database administrator Database Systems, 10th Edition

The Database Schema Schema CREATE SCHEMA AUTHORIZATION {creator}; Group of database objects that are related to each other CREATE SCHEMA AUTHORIZATION {creator}; Command is seldom used directly Database Systems, 10th Edition

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, 10th Edition

Database Systems, 10th Edition

Database Systems, 10th Edition

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, 10th Edition

Creating Table Structures (cont’d.) 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, 10th Edition

Database Systems, 10th Edition CREATE TABLE VENDOR ( V_CODE INTEGER NOT NULL UNIQUE, V_NAME VARCHAR(35) NOT NULL, V_CONTACT VARCHAR(15) NOT NULL, V_AREACODE CHAR(3) NOT NULL, V_PHONE CHAR(8) NOT NULL, V_STATE CHAR(2) NOT NULL, V_ORDER CHAR(1) NOT NULL, PRIMARY KEY (V_CODE)); CREATE TABLE PRODUCT ( P_CODE VARCHAR(10) NOT NULL UNIQUE, P_DESCRIPT VARCHAR(35) NOT NULL, P_INDATE DATE NOT NULL, P_QOH SMALLINT NOT NULL, P_MIN SMALLINT NOT NULL, P_PRICE NUMBER(8,2) NOT NULL, P_DISCOUNT NUMBER(5,2) NOT NULL, V_CODE INTEGER, PRIMARY KEY (P_CODE), FOREIGN KEY (V_CODE) REFERENCES VENDOR); For mySQL, use FOREIGN KEY (V_CODE) REFERENCES VENDOR(V_CODE)); Database Systems, 10th Edition

Database Systems, 10th Edition 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, 10th Edition

Database Systems, 10th Edition CREATE TABLE INVOICE ( INV_NUMBER NUMBER PRIMARY KEY, CUS_CODE NUMBER NOT NULL REFERENCES CUSTOMER(CUS_CODE), INV_DATE DATE NOT NULL; /* DOES NUT RUN IN mySQL */ INV_DATE DATE DEFAULT SYSDATE NOT NULL, CONSTRAINT INV_CK1 CHECK (INV_DATE > TO_DATE('01-JAN-2012','DD-MON-YYYY'))); CREATE TABLE LINE ( INV_NUMBER NUMBER NOT NULL, LINE_NUMBER NUMBER(2,0) NOT NULL, P_CODE VARCHAR(10) NOT NULL, LINE_UNITS NUMBER(9,2) DEFAULT 0.00 NOT NULL, LINE_PRICE NUMBER(9,2) DEFAULT 0.00 NOT NULL, PRIMARY KEY (INV_NUMBER,LINE_NUMBER), FOREIGN KEY (INV_NUMBER) REFERENCES INVOICE(INV_NUMBER) ON DELETE CASCADE, FOREIGN KEY (P_CODE) REFERENCES PRODUCT(P_CODE), CONSTRAINT LINE_UI1 UNIQUE(INV_NUMBER, P_CODE)); Database Systems, 10th Edition

SQL Constraints FOREIGN KEY constraint (in PRODUCT table) FOREIGN KEY (V_CODE) REFERENCES VENDOR ON UPDATE CASCADE; You can not delete a vendor from the VENDOR table if at least one product row references that vendor If a change is made in an existing VENDOR table’s V_CODE, that change must be reflected automatically in any PRODUCT table V_CODE reference Makes it impossible for a V_CODE value to exists in the PRODUCT table if there is not parallel entry in the VENDOR table

SQL Constraints NOT NULL constraint Ensures that column does not accept nulls UNIQUE constraint Ensures that all values in column are unique DEFAULT constraint (NOT IN ACCESS) Assigns value to attribute when a new row is added to table CUS_AREACODE CHAR(3) DEFAULT ‘615’ NOT NULL CHECK (CUS_AREACODE IN (‘615’, ‘713’, 931’)) CHECK constraint (NOT IN ACCESS) Validates data when attribute value is entered Minimum order amount must be at least 10 Date must be after Jan 1, 2013 CONSTRAINT INV_CHK1 CHECK (INV_DATE>TO_DATE(‘01-JAN-2012’,’DD-MON-YYYY’))

SQL Constraints MS Access and SQL Server support ON DELETE CASCADE and ON UPDATE CASCADE ON DELETE CASCADE recommended for weak entities to ensure that the deletion of a row in the strong entity automatically triggers the deletion of the corresponding rows in the dependent weak entity Oracle supports ON DELETE CASCADE Access and SQL Server do not support SET NULL, Oracle does

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 Can be in ascending or descending order … ON PRODUCT (P_PRICE DESC) Composite index Index based on two or more attributes, Often used to prevent data duplication CREATE INDEX P_INDATEX ON PRODUCT(P_INDATE); CREATE UNIQUE … ensures that no duplicates are allowed in the index (e.g., a candidate key) To delete an index use DROP INDEX P_INDATEX

Data Manipulation Commands INSERT SELECT COMMIT UPDATE ROLLBACK DELETE Database Systems, 10th Edition

Adding Table Rows INSERT Used to enter data into table Syntax: INSERT INTO tablename VALUES (value1, value2, … , valueN); value1 thru valueN are in the order the columns were defined in the CREATE TABLE NULL can be used for those values not known To insert only a few columns use INSERT INTO tabelname(col1,col2,…colN) VALUES (value1, value2, …valueN);

Adding Table Rows (cont’d.) 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

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 does not support COMMIT because it automatically saves changes after the execution of each SQL command

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 ORACLE allows you to format column data by declaring COLUMN P_PRICE FORMAT $99,9999.99 COLUMN P_DESCRIPT FORMAT A12 TRUNCATE Truncates description to first 12 characters

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 UPDATE PRODUCT SET P_INDATE=‘18-JAN-2012’, P_PRICE=17.99, P_MIN=10 WHERE P_CODE=‘13-Q2/P2’; Without a WHERE clause, all rows would be updated

Restoring Table Contents ROLLBACK Undoes changes since last COMMIT Brings data back to prechange values. Does not undo a COMMIT but undoes any changes not COMMIT’d mySQL requires START TRANSACTION; and BEGIN; Syntax: ROLLBACK; COMMIT and ROLLBACK only work with commands to add, modify, or delete table rows Database Systems, 10th Edition

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, 10th Edition

Inserting Table Rows with a SELECT Subquery Inserts multiple rows from another table (source) Uses SELECT subquery Subquery: query embedded (or nested or inner) inside another query Subquery executed first Syntax: INSERT INTO tablename SELECT columnlist FROM tablename; Database Systems, 10th Edition

SELECT Queries Fine-tune SELECT command by adding restrictions to search criteria using: Conditional restrictions Arithmetic operators Logical operators Special operators Database Systems, 10th Edition

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 ] ; WHERE V_CODE =21344 WHERE V_CODE<> 21344 WHERE PRICE <=10 WHERE P_CODE < ‘1558-WQ1’ WHERE P_INDAT>=‘20-Jan-2012’

Database Systems, 10th Edition

String comparisons are made from left to right Note that 5 will come after 44 even though the number 5 comes before the number 44. Database Systems, 10th Edition

Selecting Rows with Conditional Restrictions (cont’d.) Using comparison operators on dates Date procedures are often more software-specific than other SQL procedures Using computed columns and column aliases SQL accepts any valid expressions (or formulas) in the computed columns SELECT … ,P_QOH*P_PRICE Alias: Alternate name given to a column or table in any SQL statement SELECT … ,P_QOH*P_PRICE AS TOTVALUE

Arithmetic Operators: The Rule of Precedence Perform operations within parentheses Perform power operations Perform multiplications and divisions Perform additions and subtractions Database Systems, 10th Edition

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

Logical Operators: AND, OR, and NOT WHERE P_PRICE < 50 AND P_INDATE >’15-Jan-2012’ WHERE (P_PRICE < 50 AND P_INDATE >’15-Jan-2012’) OR V_CODE=24288 WHERE NOT(V_CODE=21344)

Special Operators BETWEEN: checks whether attribute value is within a range P_PRICE BETWEEN 50.00 AND 100 IS NULL: checks whether attribute value is null V_CODE IS NULL

Special Operators LIKE: checks whether attribute value matches given string pattern V_CONTACT LIKE ‘Smith%’ % mean any and all following or preceding characters ‘J%’ includes Johnson, Jones, July and J-231q ‘Jo%’ includes Johnson and Jones ‘%n’ includes Johnson _ means any one character may be substituted for the underscore ‘_23-456-6789’ includes 123…, 223…, 323 ‘_23-_56-678_’ includes 123-156-6781, 123-256-6782 and 823-956-6788 Oracle is case-sensitive on searches. You can use UPPER to convert column data to upper case in memory only UPPER(V_CONTACT) LIKE ‘SMITH%’ Not sure if name is Johnson or Johnsen use V_CONTACT LIKE ‘Johns_n’

Special Operators IN: checks whether attribute value matches any value within a value list V_CODE IN (21344,24288) Can be used in subqueries such as SELECT V_CODE, V_NAME FROM VENDOR WHERE V_CODE IN (SELECT V_CODE FROM PRODUCT) EXISTS: Execute a command based on the result of another query and runs only if subquery returns at least one row SELECT * FROM VENDOR WHERE EXISTS (SELECT * FROM PRODUCT WHERE P_QOH<=P_MIN);

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, 10th Edition

Changing a Column’s Data Type ALTER can be used to change data type ALTER TABLE PRODUCT MODIFY (V_CODE CHAR(5)); If the column contains data, changes can be made to the data type if those changes do not alter the type but just change the size e.g., DECIMAL (8,2) to (9,2) Some RDBMSs do not permit changes to data types unless column is empty or only let you increase the size of the field Database Systems, 10th Edition

Adding a Column Dropping a Column Use ALTER to add column Do not include the NOT NULL clause for new column as the new column will default to a value of NULL ALTER TABLE PRODUCT ADD (P_SALECODE CHAR(1)); Use ALTER to drop column Some RDBMSs impose restrictions on the deletion of an attribute ALTER TABLE VENDOR DROP COLUMN V_ORDER; Database Systems, 10th Edition

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 are useful in data updates UPDATE PRODUCT SET P_SALECODE=‘2’ WHERE P_CODE =‘1546-QQ2’; WHERE clause can use IN, logical operators, etc. UPDATE PRODUCT SET P_QOH=P_QOH+20 Any mathematical operation can be done on SET

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 (PART) Next add rows to new table using table rows from another table (PRODUCT) INSERT INTO PART (PART_CODE, PART_DESCRIPT, PART_PRICE) SELECT P_CODE,P_DESCRIPT,P_PRICE FROM PRODUCT; Or in one step CREATE TABLE PART AS SELECT P_CODE AS PART_CODE, P_DESCRIPT AS PART_DESCRIPT, P_PRICE AS PART_PRICE FROM PRODUCT;

Adding Primary and Foreign Key Designations When table is copied, integrity rules do not copy Primary and foreign keys are manually defined on new table User ALTER TABLE command ALTER TABLE tablename ADD PRIMARY KEY(fieldname); ALTER TABLE PART ADD PRIMARY KEY(PART_CODE) For foreign key, use FOREIGN KEY in place of PRIMARY KEY ALTER TABLE PART ADD FOREIGN KEY(V_CODE)REFERENCES VENDOR; You can do multiple changes in one ALTER statement One ADD follows another

Deleting a Table from the Database DROP Deletes table from database Syntax: DROP TABLE tablename; 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, 10th Edition

Additional SELECT Query Keywords 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, 10th Edition

Ordering a Listing ORDER BY clause is useful when listing order is important Syntax: SELECT columnlist FROM tablelist [WHERE conditionlist] [ORDER BY columnlist [ASC | DESC]]; Ascending order by default Database Systems, 10th Edition

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, 10th Edition

Aggregate Functions COUNT function tallies number of non-null values of an attribute Can include DISTINCT 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 Can be used with DATE fields or as MAX of a computed column SELECT MAX(A*B) … SUM computes total sum for any specified attribute AVG function format is similar to MIN and MAX Database Systems, 10th Edition

Aggregate Functions SELECT COUNT (DISTINCT V_CODE) FROM PRODUCT WHERE P_PRICE <=10.00; //TOTAL ROWS INCLUDING NULLS SELECT COUNT(*) FROM PRODUCT; SELECT MAX(P_PRICE) FROM PRODUCT; SELECT P_CODE, P_DESCRIPT, P_PRICE FROM PRODUCT WHERE P_PRICE = SELECT MAX(P_PRICE) FROM PRODUCT); USING P_PRICE = MAX(P_PRICE) DOES NOT WORK AS MAX CAN ONLY BE USED IN THE COLUMN LIST OF A SELECT STATEMENT. ALSO IN A COMAPRISON OF EQUALITY, YOU CAN ONLY USE A SINGLE VALUE TO THE RIGHT OF THE EQUALS SIGN

Grouping Data Frequency distributions created by GROUP BY clause within SELECT statement Requires aggregate function in the SELECT column list Syntax: SELECT columnlist FROM tablelist [WHERE conditionlist] [GROUP BY columnlist] [HAVING conditionlist] [ORDER BY columnlist [ASC | DESC] ] ; Database Systems, 10th Edition

Grouping Data Rows can be grouped into smaller collections and an aggregate function can then summarize the data within each collection Minimum price within each salecode Average price within each salecode

The GROUP BY clause’s columnlist must include all nonaggregate function columns in the SELECT’s columnlist The GROUP BY columnlist can include any columns from the tables in the FROM clause even if they do not appear in the SELECT’s columnlist

HAVING Clause Operates like a WHERE clause in the SELECT statement but applies to the output of the GROUP BY Limit results to products whose average price is less than $10

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 DBMS creates Cartesian product of every table When joining 3 or more tables, a join condition is needed for each pair (n-1 pairs in all) Database Systems, 10th Edition

Joining Database Tables Join condition is generally composed of an equality compariosn between the FK and the PK of related tables SELECT P_DESCRIPT, P_PRICE, V_NAME, V_CONTACT, V_AREACODE, V_PHONE FROM PRODUCT, VENDOR WHERE PRODUCT.V_CODE=VENDOR.V_CODE AND P_INDATE>’15-JAN-2012’ ORDER BY PRODUCT.PRICE;

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 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; Database Systems, 10th Edition

Recursive Joins Alias is especially useful when a table must be joined to itself Recursive query Use aliases to differentiate the table from itself Database Systems, 10th Edition

Recursive Joins Generate a list of all employees with their managers’ names

Recursive Joins 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;