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DECLARE

DECLARE ... CURSOR
DECLARE [VARIABLE] with initialization
DECLARE with DOMAIN instead of datatype
COLLATE in variable declaration
NOT NULL in variable declaration

Available in: PSQL

Description: Declares a PSQL local variable.

Syntax: 

DECLARE [VARIABLE] varname <var_spec>;

<var_spec>  ::=  <type> [NOT NULL] [<coll>] [<default>]
                   | CURSOR FOR (select-statement)
<type>      ::=  sql_datatype | [TYPE OF] domain
<coll>      ::=  COLLATE collation
<default>   ::=  {= | DEFAULT} value

  • If sql_datatype is a text type, it may include a character set.

  • Obviously, a COLLATE clause is only allowed with text types.

DECLARE ... CURSOR

Added in: 2.0

Description: Declares a named cursor and binds it to its own SELECT statement. The cursor can later be opened, used to walk the result set, and closed again. Positioned updates and deletes (using WHERE CURRENT OF) are also supported. PSQL cursors are available in triggers, stored procedures and EXECUTE BLOCK statements.

Example: 

execute block
returns (relation char(31), sysflag int)
as
declare cur cursor for 
  (select rdb$relation_name, rdb$system_flag from rdb$relations);
begin
  open cur;
  while (1=1) do
  begin
    fetch cur into relation, sysflag;
    if (row_count = 0) then leave;
    suspend;
  end
  close cur;
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 declared cursor names do not clash with any names defined later on in AS CURSOR clauses.

  • If you need a cursor to loop through an output set, it is almost always easier – and less error-prone – to use a FOR SELECT statement with an AS CURSOR clause. Declared cursors must be explicitly opened, fetched from, and closed. Furthermore, you need to check row_count after every fetch and break out of the loop if it is zero. AS CURSOR takes care of all of that automagically. However, declared cursors give you more control over the sequence of events, and allow you to operate several cursors in parallel.

  • 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). When the cursor is opened, the parameter is assigned the current value of the variable.

  • 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.

See also: OPEN cursor, FETCH cursor, CLOSE cursor

DECLARE [VARIABLE] with initialization

Changed in: 1.5

Description: In Firebird 1.5 and above, a PSQL local variable can be initialized upon declaration. The VARIABLE keyword has become optional.

Example: 

create procedure proccie (a int)
returns (b int)
as
  declare p int;
  declare q int = 8;
  declare r int default 9;
  declare variable s int;
  declare variable t int = 10;
  declare variable u int default 11;
begin
  <intelligent code here>
end

DECLARE with DOMAIN instead of datatype

Added in: 2.1

Description: In Firebird 2.1 and above, PSQL local variables and input/output parameters can be declared with a domain instead of a datatype. The TYPE OF modifier allows using only the domain's datatype and not its NOT NULL setting, CHECK constraint and/or default value.

Example: 

create procedure MyProc (a int, f ternbool)
  returns (b int, x type of bigfloat)
as
  declare p int;
  declare q int = 8;
  declare y stocknum default -1;
begin
  <very intelligent code here>
end

(This example presupposes that TERNBOOL, BIGFLOAT and STOCKNUM are domains already defined in the database.)

Warning

If you change a domain's definition, existing PSQL code using that domain may become invalid. If this happens, the system table field RDB$VALID_BLR will be set to 0 for any procedure or trigger whose code is no longer valid. If you have changed a domain, the following query will find the code modules that depend on it and report the state of RDB$VALID_BLR: 

select * from (
  select 'Procedure', rdb$procedure_name, rdb$valid_blr from rdb$procedures
    union
  select 'Trigger', rdb$trigger_name, rdb$valid_blr from rdb$triggers
) (type, name, valid)
where exists
  (select * from rdb$dependencies
   where rdb$dependent_name = name and rdb$depended_on_name = 'MYDOMAIN')

/* Replace MYDOMAIN with the actual domain name. Use all-caps if the domain
   was created case-insensitively. Otherwise, use the exact capitalisation. */

Unfortunately, not all PSQL invalidations will be reflected in the RDB$VALID_BLR field. It is therefore advisable to look at all the procedures and triggers reported by the above query, even those having a 1 in the “VALID” column.

Please notice that for PSQL modules inherited from earlier Firebird versions (including a number of system triggers, even if the database was created under Firebird 2.1 or higher), RDB$VALID_BLR is NULL. This does not indicate that their BLR is invalid.

The isql commands SHOW PROCEDURES and SHOW TRIGGERS flag modules whose RDB$VALID_BLR field is zero with an asterisk. SHOW PROCEDURE PROCNAME and SHOW TRIGGER TRIGNAME, which display individual PSQL modules, do not signal invalid BLR.

COLLATE in variable declaration

Added in: 2.1

Description: In Firebird 2.1 and above, a COLLATE clause is allowed in the declaration of text-type PSQL local variables and input/output parameters.

Example: 

create procedure GimmeText
  returns (txt char(32) character set utf8 collate unicode)
as
  declare simounao mytextdomain collate pt_br default 'não';
begin
  <stunningly intelligent code here>
end

NOT NULL in variable declaration

Added in: 2.1

Description: In Firebird 2.1 and above, a NOT NULL constraint is allowed in the declaration of PSQL local variables and input/output parameters.

Example: 

create procedure Compute(a int not null, b int not null)
  returns (outcome bigint not null)
as
  declare temp bigint not null;
begin
  <rather disappointing code here>
end
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