Predicates
A predicate specifies a condition that is true, false, or unknown about a given value, row, or group.
The following rules apply to all types of predicates:
- All values specified in a predicate must be compatible.
- An expression used in a basic, quantified, IN, or BETWEEN predicate must not result in a character string with a length attribute greater than 4000, a graphic string with a length attribute greater than 2000, or a LOB string of any size.
- The value of a host variable can be null (that is, the variable may have a negative indicator variable).
- The code page conversion of operands of predicates involving two or more operands, with the exception of LIKE, is done according to the rules for string conversions.
- Use of a structured type value is limited to the NULL predicate and the TYPE predicate.
- In a Unicode database, all predicates that accept a character or graphic string will accept any string type for which conversion is supported.
A fullselect is a form of the SELECT statement that, when used in a predicate, is also called a subquery.
Row-value-expression
The operand of several predicates (basic, quantified, and IN) can be expressed as a row value expression:
A row value expression returns a single row that consists of one or more fields. The field values can be specified as a list of expressions. The number of fields that are returned by the row value expression is equal to the number of expressions that are specified in the list.