6.8 EXECUTE BLOCK

Used forCreating an anonymous block of PSQL code in DSQL for immediate execution

Available inDSQL

Syntax

EXECUTE BLOCK [(<inparams>)]
  [RETURNS (<outparams>)]
  <psql-module-body>
 
<inparams> ::=  <param_decl> = ? [, <inparams> ]
 
<outparams> ::=  <param_decl> [, <outparams>]
 
<param_decl> ::=
  paramname <domain_or_non_array_type> [NOT NULL] [COLLATE collation]
 
<domain_or_non_array_type> ::=
  !! See Scalar Data Types Syntax !!
 
<psql-module-body> ::=
  !! See Syntax of a Module Body !!

Table 6.8.1 Arguments for the EXECUTE BLOCK Statement Parameters

Executes a block of PSQL code as if it were a stored procedure, optionally with input and output parameters and variable declarations. This allows the user to perform on-the-fly PSQL within a DSQL context.

6.8.1 Examples

1. This example injects the numbers 0 through 127 and their corresponding ASCII characters into the table ASCIITABLE:

   EXECUTE BLOCK
   AS
   declare i INT = 0;
   BEGIN
     WHILE (i < 128) DO
     BEGIN
       INSERT INTO AsciiTable VALUES (:i, ascii_char(:i));
       i = i + 1;
     END
   END

2. The next example calculates the geometric mean of two numbers and returns it to the user:

   EXECUTE BLOCK (x DOUBLE PRECISION = ?, y DOUBLE PRECISION = ?)
   RETURNS (gmean DOUBLE PRECISION)
   AS
   BEGIN
     gmean = SQRT(x*y);
     SUSPEND;
   END

   Because this block has input parameters, it has to be prepared first. Then the parameters can be set and the block executed. It depends on the client software how this must be done and even if it is possible at all — see the notes below.

3. Our last example takes two integer values, smallest and largest. For all the numbers in the range smallest…​largest, the block outputs the number itself, its square, its cube and its fourth power.

   EXECUTE BLOCK (smallest INT = ?, largest INT = ?)
   RETURNS (number INT, square BIGINT, cube BIGINT, fourth BIGINT)
   AS
   BEGIN
     number = smallest;
     WHILE (number <= largest) DO
     BEGIN
       square = number * number;
       cube   = number * square;
       fourth = number * cube;
       SUSPEND;
       number = number + 1;
     END
   END

   Again, it depends on the client software if and how you can set the parameter values.

6.8.2 Input and output parameters

Executing a block without input parameters should be possible with every Firebird client that allows the user to enter his or her own DSQL statements. If there are input parameters, things get trickier: these parameters must get their values after the statement is prepared, but before it is executed. This requires special provisions, which not every client application offers. (Firebird’s own isql, for one, doesn’t.)

The server only accepts question marks (?) as placeholders for the input values, not :a, :MyParam etc., or literal values. Client software may support the :xxx form though, and will preprocess it before sending it to the server.

If the block has output parameters, you must use SUSPEND or nothing will be returned.

Output is always returned in the form of a result set, just as with a SELECT statement. You can’t use RETURNING_VALUES or execute the block INTO some variables, even if there is only one result row.

PSQL Links

For more information about writing PSQL, consult Chapter Procedural SQL (PSQL) Statements.

6.8.3 Statement Terminators

Some SQL statement editors — specifically the isql utility that comes with Firebird and possibly some third-party editors — employ an internal convention that requires all statements to be terminated with a semi-colon. This creates a conflict with PSQL syntax when coding in these environments. If you are unacquainted with this problem and its solution, please study the details in the PSQL chapter in the section entitled Switching the Terminator in isql.