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FOR SELECT INTO ... DO
Available in: PSQL
Description
Executes a SELECT statement and retrieves the result set. In each iteration of the loop, the field values of the current row are copied into local variables. Adding an AS CURSOR clause enables positioned deletion or update of the current row. FOR SELECT statements may be nested.
Syntax
FOR <select-stmt> INTO <var> [, <var> ...] [AS CURSOR name] DO <psql-stmt> <select-stmt> ::= A valid SELECT statement. <var> ::= A PSQL variable name, optionally preceded by ":" <psql-stmt> ::= A single statement or a block of PSQL code.
- The SELECT statement may contain named SQL parameters, like in select name || :sfx from names where number = :num. Each parameter must be a PSQL variable that has been declared previously (this includes any in/out params of the PSQL module).
- Caution! If the value of a PSQL variable that is used in the SELECT statement changes during execution of the loop, the statement may (but will not always) be re-evaluated for the remaining rows. In general, this situation should be avoided. If you really need this behaviour, test your code thoroughly and make sure you know how variable changes affect the outcome. Also be advised that the behaviour may depend on the query plan, in particular the use of indices. As it is currently not strictly defined, it may change in some future version of Firebird.
Examples
create procedure shownums returns (aa int, bb int, sm int, df int) as begin for select distinct a, b from numbers order by a, b into :aa, :bb do begin sm = aa + bb; df = aa - bb; suspend; end end create procedure relfields returns (relation char(32), pos int, field char(32)) as begin for select rdb$relation_name from rdb$relations into :relation do begin for select rdb$field_position + 1, rdb$field_name from rdb$relation_fields where rdb$relation_name = :relation order by rdb$field_position into :pos, :field do begin if (pos = 2) then relation = ' "'; -- for nicer output suspend; end end end
AS CURSOR clause
Available in: PSQL
Added in: IB
Description
The optional AS CURSOR clause creates a named cursor that can be referenced (after WHERE CURRENT OF) within the FOR SELECT loop in order to update or delete the current row. This feature was already added in InterBase, but not mentioned in the Language Reference.
Example
create procedure deltown (towntodelete varchar(24)) returns (town varchar(24), pop int) as begin for select town, pop from towns into :town, :pop as cursor tcur do begin if (town = towntodelete) then delete from towns where current of tcur; else suspend; end end
Notes:
- A FOR UPDATE clause is allowed in the SELECT statement, but not required for a positioned update or delete to succeed.
- Make sure that cursor names defined here do not clash with any names created earlier on in DECLARE CURSOR statements.
- AS CURSOR is not supported in FOR EXECUTE STATEMENT loops, even if the statement to execute is a suitable SELECT query.