PREPARE statement [ESQL]

Description

Prepares a statement to be executed later or used for a cursor.

Syntax

PREPARE statement-name 
FROM statement
... [ DESCRIBE describe-type INTO [ [ SQL ] DESCRIPTOR ] descriptor ]
... [ WITH EXECUTE ]

Parameters

statement-name:: identifier or host-variable

statement:: string, or host-variable

describe-type:: { ALL | BIND VARIABLES | INPUT | OUTPUT | SELECT LIST } ... { LONG NAMES [ [ OWNER.]TABLE.]COLUMN ] | WITH VARIABLE RESULT }

Examples

Example 1

The following statement prepares a simple query:

EXEC SQL PREPARE employee_statement FROM
'SELECT emp_lname FROM employee';

Usage

The PREPARE statement prepares a SQL statement from the statement and associates the prepared statement with statement-name. This statement name is referenced to execute the statement, or to open a cursor if the statement is a SELECT statement. Statement-name may be a host variable of type a_sql_statement_number defined in the sqlca.h header file that is automatically included. If an identifier is used for the statement-name, then only one statement per module may be prepared with this statement-name.

If a host variable is used for statement-name, it must have the type short int. There is a typedef for this type in sqlca.h called a_sql_statement_number. This type is recognized by the SQL preprocessor and can be used in a DECLARE section. The host variable is filled in by the database during the PREPARE statement and need not be initialized by the programmer.

If the DESCRIBE INTO DESCRIPTOR clause is used, the prepared statement is described into the specified descriptor. The describe type may be any of the describe types allowed in the DESCRIBE statement.

If the WITH EXECUTE clause is used, the statement is executed if and only if it is not a CALL or SELECT statement, and it has no host variables. The statement is immediately dropped after a successful execution. If the PREPARE and the DESCRIBE (if any) are successful but the statement cannot be executed, a warning SQLCODE 111, SQLSTATE 01W08 is set, and the statement is not dropped.

The DESCRIBE INTO DESCRIPTOR and WITH EXECUTE clauses may improve performance, as they cut down on the required client/server communication.