1 SQL II CIS*2450 Advanced Programming Concepts

2 Data Types INTEGER –numbers without a decimal point –range is to SMALLINT –like INTEGER but smaller range to DECIMAL(p,q) –decimal numbers p digits long with q of these being decimal places $99, = DECIMAL(7,2)

3 Data Types CHAR(n) –character string n characters long VARCHAR(n) –string up to n characters long DATE –dates in the form DD-MON-YY or MM/DD/YYYY

4 Nulls The values for some columns may be unknown when a row is added to a table. SQL provides a special character referred to as a null data value or a null. –3 meanings: unknown, not applicable, missing In any system that supports null values, SQL allows one to choose whether or not to allow nulls for each column.

5 Nulls CREATE TABLE COMPUTER ( COMPID DECIMAL (2) NOT NULL, MFGNAME CHAR (15) NOT NULL, MFGMODEL CHAR (25), PROCTYPE DECIMAL (7,2), PRIMARY KEY(COMPID) ) integrity constraints

6 Comparison Operators Comparison Operators Meaning = Equal to < Less than > Greater than <= Less than or equal to >= Greater than or equal to <> or != Not equal to (implementation dependent)

7 Comparison Operators The BETWEEN feature allows one to specify a range of values without using the comparison operators. SELECT PACKID, PACKNAME, PACKCOST FROM PACKAGE WHERE PACKCOST BETWEEN 200 AND 400 SELECT PACKID, PACKNAME, PACKCOST FROM PACKAGE WHERE PACKCOST > 200 AND PACKCOST < 400

8 Compound Conditions Compound conditions are formed by connecting two or more simple statements using AND, OR, and NOT. Simple conditions connected by AND must all be TRUE for the compound statement to be TRUE.

9 Compound Conditions Simple conditions connected by OR: the compound statement is TRUE if any one (or both) of the simple conditions is TRUE. Preceding a condition by the word NOT reverses the truth of the original condition.

10 Compound Conditions SELECT PACKNAME FROM PACKAGE WHERE PACKTYPE <> 'Database' SELECT PACKNAME FROM PACKAGE WHERE NOT (PACKTYPE = 'Database')

11 Ordering The order of rows in a table is immaterial so one cannot predict the order of responses to queries. If the order is important then one can specifically request that the results be displayed in a desired order with the ORDER BY clause. SELECT EMPNUM, EMPNAME, EMPPHONE FROM EMPLOYEE ORDER BY EMPNAME

12 Ordering One can also sort on multiple keys and use descending order. The keys to be used are listed in order of importance after ORDER BY, and if this is followed by DESC then the ordering is descending. SELECT PACKID, PACKNAME, PACKTYPE, PACKCOST FROM PACKAGE ORDER BY PACKTYPE, PACKCOST DESC

13 Ordering ORDER BY PACKTYPE, PACKCOST DESC PACKIDPACKNAMEPACKTYPEPACKCOST 14OracleDatabase DB2Database AccessDatabase500 23Visual StudioIDE800 15C++BuilderIDE400

14 Aggregate Functions Built-in Function Meaning COUNT Number of rows satisfying the WHERE clause SUM Sum of the values in a column for all rows satisfying the WHERE clause AVG Average of the values in a column for all rows satisfying the WHERE clause

15 Aggregate Functions Built-in Function Meaning MAX Largest value in a column for all rows satisfying the WHERE clause MIN Smallest value in a column for all rows satisfying the WHERE clause

16 Aggregate Functions SELECT COUNT(PACKID), MAX(PACKCOST) FROM PACKAGE COUNT1 MAX

17 Aggregate Functions The AS operator is used in the following examples to name the resultant column.

18 Aggregate Functions SELECT COUNT(*) AS NUM_SUPPLIERS FROM SP NUM_SUPPLIERS 5 This counts the number of active suppliers since the COUNT(*) means count all the rows of SP –some suppliers may be duplicates!

19 Aggregate Functions SELECT COUNT(DISTINCT SP.SNO) AS NUM_SUPPLIERS FROM SP NUM_SUPPLIERS 4 More accurate: This counts the number of different suppliers supplying parts.

20 Aggregate Functions SELECT SUM(SP.QTY) AS QTY_P2 FROM SP WHERE SP.PNO = 'P2' This calculates the total quantity of part P2.

21 Aggregate Functions SELECT SP.PNO, SUM(SP.QTY) AS QTY FROM SP GROUP BY SP.PNO SP.PNOQTY P1600 P2400 P4400 GROUP BY creates groups based upon column entries. SUM adds within group. This produces a table of part numbers and their total quantities for each part supplied.

22 Nested Queries Can place one query inside another. The inner query is called a subquery and is executed first. SELECT PACKID, PACKNAME FROM PACKAGE WHERE PACKTYPE= 'Database‘ AND PACKCOST > ( SELECT AVG (PACKCOST) FROM PACKAGE WHERE PACKTYPE = 'Database' )

23 Client-Server and SQL An SQL-agent is an application which includes some SQL operations. The application is bound to an SQL-client which is used to communicate with an SQL-server. The server carries out the database operations. The client and server are connected through the CONNECT operation. After the transactions are completed, use the DISCONNECT statement.