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SQL Language Extension: EXECUTE BLOCK

Function:
Allow execute PL-SQL block as if it is stored procedure.
Supports input and output parameters

Autor:
Vlad Horsun <horsun@kdb.dp.ua>

Syntax:
EXECUTE BLOCK [ (param datatype = ?, param datatype = ?, ...) ]
[ RETURNS (param datatype, param datatype, ...) }
AS
[DECLARE VARIABLE var datatype; ...]
BEGIN
...
END

Client-side:
The call isc_dsql_sql_info with parameter isc_info_sql_stmt_type returns
- isc_info_sql_stmt_select, if block has output parameters.
Semantics of a call is similar to SELECT query - client has open cursor,
can fetch data from it, and must close it after use.

- isc_info_sql_stmt_exec_procedure, if block has no output parameters.
Semantics of a call is similar to EXECUTE query - client has no cursor,
execution runs until first SUSPEND or end of block

The client should preprocess only head of the SQL statement or use '?'
instead of ':' as parameter indicator because in a body of the block may be links
to local variables and \ or parameters with a colon ahead.

Example:
User SQL is
EXECUTE BLOCK (X INTEGER = :X) RETURNS (Y VARCHAR)
AS
DECLARE V INTEGER;
BEGIN
INSERT INTO T(...) VALUES (... :X ...);

SELECT ... FROM T INTO :Y;
SUSPEND;
END

Preprocessed SQL is
EXECUTE BLOCK (X INTEGER = ?) RETURNS (Y VARCHAR)
AS
DECLARE V INTEGER;
BEGIN
INSERT INTO T(...) VALUES (... :X ...);

SELECT ... FROM T INTO :Y;
SUSPEND;
END