Principles of Dynamic SQL

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Dynamic SQL enables you to execute SQL statements placed in a string variable instead of explicitly writing the statements inside a program. This allows SQL statements to be constructed within an application program. These facilities are typically used in interactive environments, where SQL statements are submitted to the application program from the terminal.

An example of when dynamic SQL is needed would be a program for interactive SQL, where any correct SQL statement may be entered at the terminal and processed by the application. Limited dynamic facilities may however be provided by relatively simple application programs.

SQL Statements and Dynamic SQL

The following classes of SQL statements may be submitted to programs using dynamic SQL. Statements excluded from dynamic applications are declarations, diagnostic statements and dynamic SQL statements themselves.

• Access control statements:

  ENTER

  LEAVE

• Data definition statements:

  CREATE

  ALTER

  COMMENT

  DROP

• Security control statements:

  GRANT

  REVOKE

• Transaction control statements:

  SET SESSION

  SET TRANSACTION

  START

  COMMIT

  ROLLBACK

• Data manipulation statements:

  CALL

  SELECT

  SELECT INTO

  INSERT

  UPDATE

  UPDATE CURRENT

  DELETE

  DELETE CURRENT

• System administration statements:

  CREATE BACKUP

  ALTER DATABANK RESTORE

  SET DATABASE

  SET DATABANK

  SET SHADOW

  UPDATE STATISTICS

Submitting Statements

Statements may be submitted to dynamic SQL applications in two forms:

• Fully defined statements, written exactly as they would be submitted to interactive SQL. For example:

 GRANT SELECT ON mimer_store_book.details TO mimer_admin_group
 
 SELECT code, country
    FROM mimer_store.countries
 
 SELECT price
    INTO :PRICE
    FROM mimer_store.items
    WHERE item_id = :ITEM_ID
 

• Statements with parameter markers, which identify positions where the value of a host variable will be inserted when the statement is executed or the cursor is opened. A parameter marker is represented by a question mark ?. For example:

 UPDATE mimer_store.currencies
    SET exchange_rate = ?
    WHERE code = ?
 
 DELETE FROM countries
    WHERE code = ?
 
 SELECT currency, exchange_rate * ?
    FROM mimer_store.currencies
    WHERE code IN (SELECT currency_code
                      FROM mimer_store.countries
                      WHERE code like ? || '%')
 

   Statements submitted with parameter markers are equivalent to normal embedded statements using host variables, except that the statements are defined at run-time.

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