Example: custlist.4gl (Function custlist_query)

The custlist_query function implements the CONSTRUCT instruction to get an SQL condition that will be used in the SELECT statement to filter customer table rows.

The custlist_query function in custlist.4gl:

  1 PRIVATE FUNCTION custlist_query() RETURNS STRING
  2   DEFINE sql_cond STRING
  3 
  4   CLEAR FORM
  5 
  6   LET int_flag = FALSE
  7   CONSTRUCT BY NAME sql_cond ON cust_num, cust_name
  8 
  9   IF int_flag THEN
 10      RETURN NULL
 11   ELSE
 12      RETURN sql_cond
 13   END IF

Note:

Line 1 defines the function with not parameters, and a single return value of type STRING.
Line 4 clears all form fields with the CLEAR FORM instruction.
Line 6 resets the int_flag register to FALSE.
Line 7 declares the CONSTRUCT instruction. For more details, go to Tutorial Chapter 4: Query by Example.
Lines 9 thru 13: Depending on the int_flag, we return the SQL condition or NULL, if the user has selected the Cancel button.