SQL Language Extension: EXECUTE STATEMENT

   Implements capability to take a string which is a valid dynamic SQL
   statement and execute it as if it had been submitted to DSQL.  
   Available in triggers and stored procedures. 

Author:
   Alex Peshkoff <pes@insi.yaroslavl.ru>;

Syntax may have three forms.

Syntax  1 
========

EXECUTE STATEMENT <string>;

Description

Executes <string> as SQL operation. It should not return any data rows.
Following types of SQL operators may be executed:

   * Insert, Delete and Update.
   * Execute Procedure.
   * Any DDL (except Create/Drop Database).

Sample:

CREATE PROCEDURE DynamicSampleOne (Pname VARCHAR( 100 ))
AS
DECLARE VARIABLE Sql VARCHAR( 1024 );
DECLARE VARIABLE Par INT;

BEGIN
SELECT MIN(SomeField) FROM SomeTable INTO :Par;
Sql = 'EXECUTE PROCEDURE ' || Pname || '(';
Sql = Sql || CAST(Par AS VARCHAR( 20 )) || ')';
EXECUTE STATEMENT Sql;
END


Syntax  2 
=========

EXECUTE STATEMENT <string> INTO :var1, ., :varn;

Description

Executes <string> as SQL operation, returning single data row. Only
singleton SELECT operators may be executed with this form of EXECUTE
STATEMENT.

Sample:

CREATE PROCEDURE DynamicSampleTwo (TableName VARCHAR( 100 ))
AS
DECLARE VARIABLE Par INT;

BEGIN
EXECUTE STATEMENT 'SELECT MAX(CheckField) FROM ' || TableName INTO :Par;
IF (Par >  100 ) THEN
  EXCEPTION Ex_Overflow 'Overflow in ' || TableName;
END


Syntax  3 
========

FOR EXECUTE STATEMENT <string> INTO :var1, ., :varn DO
<compound-statement>;

Description

Executes <string> as SQL operation, returning multiple data rows. Any SELECT
operator may be executed with this form of EXECUTE STATEMENT.

Sample:

CREATE PROCEDURE DynamicSampleThree (TextField VARCHAR( 100 ), TableName VARCHAR( 100 ))
	RETURNING_VALUES (Line VARCHAR( 32000 ))
AS
DECLARE VARIABLE OneLine VARCHAR( 100 );

BEGIN
Line = '';
FOR EXECUTE STATEMENT 'SELECT ' || TextField || ' FROM ' || TableName
	INTO :OneLine
DO
  IF (OneLine IS NOT NULL) THEN
    Line = Line || OneLine || ' ';
SUSPEND;
END