ESQL complex comparison operators

This topic describes ESQL's complex comparison operators (predicates). For information about ESQL's simple comparison operators, see ESQL simple comparison operators.

Operator BETWEEN
The operator BETWEEN allows you to test whether a value lies between two BOUNDARY VALUES.

This operator exists in two forms, SYMMETRIC and ASYMMETRIC (which is the default if neither is specified). The SYMMETRIC form is equivalent to:

(source >= boundary1 AND source <= boundary2) OR
(source >= boundary2 AND source <= boundary1)

The ASYMMETRIC form is equivalent to:

source >= boundary1 AND source <= boundary2

The ASYMMETRIC form is simpler but returns only the result that you expect when the first boundary value has a smaller value than the second boundary. It is only useful when the boundary condition expressions are literals.

If the operands are of different types, special rules apply. These are described in Implicit casts.

Operator EXISTS
The operator EXISTS returns a boolean value indicating whether a SELECT function returned one or more values (TRUE) or none (FALSE).
EXISTS(SELECT * FROM something WHERE predicate)
Operator IN
The operator IN allows you to test whether a value is equal to one of A LIST OF VALUES.

The result is TRUE if the left operand is not NULL and is equal to one of the right operands. The result is FALSE if the left operand is not NULL and is not equal to any of the right operands, none of which have NULL values. Otherwise the result is UNKNOWN. If the operands are of different types, special rules apply. These are described in Implicit casts.

Operator IS
The operator IS allows you to test whether an expression has returned A SPECIAL VALUE.

The primary purpose of the operator IS is to test whether a value is NULL. The comparison operator (=) does not allow this because the result of comparing anything with NULL is NULL.

IS also allows you to test for the Boolean values TRUE and FALSE, and the testing of decimal values for special values. These are denoted by INF, +INF, -INF, NAN (not a number), and NUM (a valid number) in any mixture of case. The alternative forms +INFINITY, -INFINITY, and NUMBER are also accepted.

If applied to non-numeric types, the result is FALSE.

Operator LIKE
THE OPERATOR LIKE SEARCHES FOR STRINGS THAT MATCH A CERTAIN PATTERN.

The result is TRUE if none of the operands is NULL and the source operand matches the pattern operand. The result is FALSE if none of the operands is NULL and the source operand does not match the pattern operand. Otherwise the result is UNKNOWN.

The pattern is specified by a string in which the percent (%) and underscore (_) characters have a special meaning:

  • The underscore character _ matches any single character.
    For example, the following finds matches for IBM and for IGI, but not for International Business Machines or IBM Corp:
    Body.Trade.Company LIKE 'I__'
  • The percent character % matches a string of zero or more characters.
    For example, the following finds matches for IBM, IGI, International Business Machines, and IBM Corp:
    Body.Trade.Company LIKE 'I%'

To use the percent and underscore characters within the expressions that are to be matched, precede the characters with an ESCAPE character, which defaults to the backslash (\) character.

For example, the following predicate finds a match for IBM_Corp.

Body.Trade.Company LIKE 'IBM\_Corp'

You can specify a different escape character by using the ESCAPE clause. For example, you could also specify the previous example like this:

Body.Trade.Company LIKE 'IBM$_Corp' ESCAPE '$'
Operator SINGULAR
The operator SINGULAR returns a boolean value of TRUE if the list has exactly one element, otherwise it returns FALSE.
Related concepts
Message flows overview
Message mappings overview
Related tasks
Developing message flows
Developing ESQL
Related reference
ESQL simple comparison operators
Built-in nodes
ESQL reference
ROW and LIST comparisons
Implicit casts