Boolean comparisons

Boolean comparisons can test any type of expression for equality or inequality, null values, or set membership, using these operators:

• relational operators to test for equality or inequality
• IS NULL (and IS NOT NULL) to test for null values
• LIKE or MATCHES to compare character strings
• IN to test for set membership
• BETWEEN..AND to test for range

 

IN and BETWEEN..AND operators are valid only in SQL statements. They cause a compilation error if you include them in other 4GL statements except for the WHERE clause of a .per form that includes the COLOR attribute.

 

Boolean expressions in the CASE, IF, or WHILE statements (or in the WHERE clause of a COLOR attribute specification) return FALSE if any element of the comparison is null, unless it is the operand of the IS NULL or IS NOT NULL operator.

NULL test is used to detect and exclude null values in boolean comparisons.