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FOR SELECT ... INTO ... DO

AS CURSOR clause

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 deletes and updates. 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. And as it is currently not strictly defined, it may also 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.

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