Comparison Conditions (Boolean Expressions)
Comparison conditions are often called Boolean expressions because
they return a TRUE or FALSE result.
Six kinds of Boolean operators can specify a comparison condition:
- Relational operators
- [NOT] BETWEEN AND operators
- [NOT] IN operators
- IS [NOT] NULL operators
- Trigger-type operators
- [NOT] LIKE or MATCHES operators
Their syntax is summarized in this diagram and explained in the
sections that follow.
(explicit id coco001)
coco001
(explicit id coco002)
coco002
(explicit id coco003)
coco003
(explicit id coco004)
coco004
(explicit id coco006)
coco006
(explicit id coco007)
coco007
(explicit id coco008)
coco008
Comparison Conditions
{ <Expression>[] <Relational Operator>[] <Expression>[] | <Expression>[] [ NOT ] BETWEEN <Expression>[] AND <Expression>[] | [] <IN Condition>[] | { column | expression } IS [ NOT ] NULL | [] <Trigger-Type Operator> [] | { string | column } [ NOT ] { LIKE | []MATCHES } { string [ ESCAPE 'char' ] | column } }
| Element | Description | Restrictions | Syntax |
|---|---|---|---|
| char | An ASCII character to be the escape character in the quoted string. Single ( ' ) and double ( " ) quotation marks are not valid as char. | See ESCAPE with LIKE and ESCAPE with MATCHES | Quoted String |
| column | Name of a column (or a field of a ROW-type column) whose data value is compared to NULL, to string, or to another column | Can be qualified by the identifier, synonym, or alias of a table or view | See Column Name |
| expression | An SQL expression that returns a single value | Must return a single value | Expression |
| string | A string delimited by single ( ' ) or double ( " ) quotation marks | Both delimiters must be identical | See Quoted String |
The following sections describe the different types of comparison
conditions:
For a discussion of comparison conditions in the context of the
SELECT statement, see Using a Condition in the WHERE Clause.
Warning: A literal DATE
or DATETIME value in a comparison condition should specify 4 digits
for the year. When you specify a 4-digit year, the DBCENTURY environment
variable has no effect on the result. When you specify a 2-digit year, DBCENTURY can
affect how the database server interprets the comparison condition,
which might not work as you intended. For more information about DBCENTURY,
see the Informix® Guide to SQL:
Reference.
1 Informix® extension
2 See Expression
3 See Relational Operator
4 See IN Condition
5 See Quoted String
6 SPL trigger routines only