1 A Guide to SQL Chapter 2

2 Introduction Mid-1970s: SQL developed under the name SEQUEL at IBM by San Jose research facilities to be the data manipulation language for IBM’s prototype relational model DBMS, System R 1980: language renamed SQL to avoid confusion with an unrelated hardware product called SEQUEL Currently: SQL used as the data manipulation language for IBM’s current relational DBMS, DB2 Most relational DBMSes use a version of SQL

3 SQL Text Case Sensitivity SQL is not case sensitive Type commands using uppercase or lowercase letters Exception: when inserting character values into a table, use the correct case

4 Qualifying Names To associate the correct table with the column name write both the table name and the column name, separated by a period CUSTOMER.SLSREP_NUMBER SALES_REP.SLSREP_NUMBER This technique of including the table name with the column name is known as qualifying the names

5 Database Creation The SQL command used to describe the layout of a table is CREATE TABLE followed by the name of the table to be created and the names and data types of the columns that comprise the table in parentheses Data type indicates the type of data that the column can contain (for example, characters, numbers, or dates)

6 Typical Column Naming Conventions The name cannot be longer than 18 characters (in Oracle, names can be up to 30 characters in length) The name must start with a letter The name can contain letters, numbers, and underscores ( _ ) The name cannot contain spaces

7 Create Table Command for SALES_REP Table

8 Common Data Types

9 SQL Commands Commands can be entered in a free format no rule says that a particular word must begin in a particular position on a line the manner in which the command is written simply makes the command more readable Press the Enter key at the end of each line and then continue typing the command on the next line Indicate the end of a command line by typing a semicolon

10 Dropping a Table Use the DROP TABLE command to delete a table The command DROP TABLE is followed by the name of the table you want to delete and a semicolon. DROP TABLE SALES_REP; Note when a table is dropped, any data that you entered into the table is dropped

11 Implementation of Nulls CREATE TABLE SALES_REP (SLSREP_NUMBER CHAR(2) NOT NULL, LAST CHAR(10) NOT NULL, FIRST CHAR (5) NOT NULL, STREET CHAR(15), CITY CHAR(15), STATE CHAR(2), ZIP_CODE CHAR(5), TOTAL_COMMISSION DECIMAL(7,2), COMMISSION_RATE DECIMAL(3,2) );

12 Loading a Table with Data Add necessary rows to each table using the INSERT command When adding rows to character (CHAR) columns, make sure to enclose the values in single quotation marks (for example, ‘Jones’)

13 INSERT Command

14 Editing In Oracle, the most recent command entered is stored in the command buffer The easiest way to edit a command is to use the Notepad (type “Edit” at the SQL prompt).

15 Using an Editor to Modify the INSERT Command

16 The INSERT Command with Nulls To enter a null value into a table, use a special format of the INSERT command In this special format, identify the names of the columns that will accept non-null values, and then list only these non-null values after the VALUES command

17 Inserting a Row Containing Null Values

18 Correcting Errors in the Database After reviewing the data in the table changes may have to be made to the value in a column Use the UPDATE command shown in Figure 2.13 to correct errors

19 Modifying the Contents of a Column

20 DELETE Command To delete a record, use the DELETE command The command in Figure 2.14 deletes any row on which the sales rep number is 18

21 Deleting a Row

22 cre_cust.SQL To run the cre_cust.SQL file Save the file Close the editor (and full path if stored in another folder) After creating the table, another file could be created containing all the necessary INSERT commands to add the necessary records to the table Each command must end with a semicolon

23 Describing a Table Use the DESCRIBE command to describe the layout of a table The DESCRIBE command, as shown in Figure 2.23 lists all the columns in the SALES_REP table and their corresponding data types

24 DESCRIBE Command for SALES_REP Table