Defining and Manipulating Data

You embed data definition and data manipulation commands in the PROCEDURE DIVISION.

Data Definition

You can embed the following SQL commands to create objects or change existing objects:



      ALTER DBEFILE         CREATE INDEX           DROP GROUP

      ALTER TABLE           CREATE TABLE           DROP INDEX

      CREATE DBEFILE        CREATE VIEW            DROP MODULE

      CREATE DBEFILESET     DROP DBFILE            DROP TABLE

      CREATE GROUP          DROP DBFILESET         DROP VIEW

Data definition commands are useful for such activities as creating temporary tables or views to simplify data manipulation or creating an index that improves the program's performance:



        EXEC SQL CREATE INDEX PARTNAMEINDEX

                           ON PURCHDB.PARTS (PARTNAME);

        END-EXEC.

The index created with this command expedites data access operations based on partial key values:



        EXEC SQL SELECT PARTNAME

                  INTO :PARTNAME

                   FROM PURCHDB.PARTS

                  WHERE PARTNAME LIKE :PARTIAL-KEY

        END-EXEC.

Data Manipulation

SQL has four basic data manipulation commands:

SELECT: retrieves data.
INSERT: adds rows.
DELETE: deletes rows.
UPDATE: changes column values.

These four commands can be used for various types of data manipulation operations:

Simple data manipulation: operations that retrieve a single row, insert a single row, or delete or update a limited number of rows.
Sequential table processing: operations that use a cursor to operate on one row at a time within a set of rows. A cursor is a pointer the program advances through the set of rows.
Bulk operations: operations that manipulate multiple rows with a single execution of a data manipulation command.
Dynamic operations: operations specified by the user at run time.

In all non-dynamic data manipulation operations, you use host variables to pass data back and forth between your program and the DBEnvironment. Host variables can be used in the data manipulation commands wherever the syntax in the allows them.

The SELECT command shown at 8 in Figure 3-1 “Sample Program COBEX2 ” retrieves the row from PURCHDB.PARTS that contains a part number matching the value in the host variable named in the WHERE clause (PARTNUMBER). The three values in the row retrieved are stored in three host variables named in the INTO clause (PARTNUMBER, PARTNAME, and SALESPRICE). An indicator variable (SALESPRICEIND) is also used in the INTO clause, to flag the existence of a null value in column SALESPRICE:



        EXEC SQL SELECT  PARTNUMBER, PARTNAME, SALESPRICE

                   INTO :PARTNUMBER,

                        :PARTNAME

                        :SALESPRICE :SALESPRICEIND

                   FROM  PURCHDB.PARTS

                  WHERE  PARTNUMBER = :PARTNUMBER

        END-EXEC.

You can also use host variables in non-SQL statements; in this case, omit the colon:



        MOVE RESPONSE TO SALESPRICE

        EXEC SQL SELECT  COUNT(PARTNUMBER)

                   INTO :PART-COUNT

                   FROM  PURCHDB.PARTS

                  WHERE  SALESPRICE > :SALESPRICE

        END-EXEC.

All host variables used in the PROCEDURE DIVISION must be declared in the DATA DIVISION, as discussed earlier in this chapter under "Declaring Host Variables".

Defining and Manipulating Data

Technical documentation

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Data Definition

Data Manipulation