|
|
[NOT]
|
|
predicate |
|
|
|||
| (search-condition) | ||||||||
| search-condition |
|
AND
|
|
search-condition | ||||
OR
|
||||||||
This document covers the following topics:
Search Condition
A search-condition can consist
of a simple predicate
or of multiple search-conditions
combined with the Boolean operators AND, OR and
NOT, and parentheses if required to indicate a desired order of
evaluation.
Example
DEFINE DATA LOCAL 01 NAME (A20) 01 AGE (I2) END-DEFINE ... SELECT * INTO NAME, AGE FROM SQL-PERSONNEL WHERE AGE = 32 AND NAME > 'K' END-SELECT ...
Predicate
A predicate specifies a
condition that can be "true", "false" or
"unknown".
In a search-condition,
a predicate can consist of a simple or
complex comparison operation or other kinds of conditions.
Example:
SELECT NAME, AGE
INTO VIEW PERS
FROM SQL-PERSONNEL
WHERE AGE BETWEEN 20 AND 30
0R AGE IN ( 32, 34, 36 )
AND NAME LIKE '%er'
...
Note:
The percent sign (%) may conflict with
Natural terminal commands. If
so, you must define a terminal command control character different from
%; see Changing the Terminal
Command Control Character in the Terminal
Commands documentation.
The individual predicates are explained in the following topics (for further information on predicates, please refer to the relevant literature). According to the syntax above, they are called as follows:
Comparison Predicate
|
|
scalar-expression | comparison | scalar-expression |
|
||
| row-value-expression |
|
= |
|
row-value-expression | ||
| <> | ||||||
A comparison predicate compares two values or a set of values with another set of values.
See information on scalar-expression.
Comparison
|
|
=
|
|
<
|
||
>
|
||
<=
|
||
>=
|
||
< >
|
comparison can be any of the
following operators:
=
|
equal to |
|---|---|
<
|
less than |
>
|
greater than |
<=
|
less than or equal to |
>=
|
greater than or equal to |
<>
|
not equal to |
Subquery
| (select-expression) |
A subquery is a
select-expression that is nested inside
another such expression.
Example:
DEFINE DATA LOCAL
1 #NAME (A20)
1 #PERSNR (I4)
END-DEFINE
...
SELECT NAME, PERSNR
INTO #NAME, #PERSNR
FROM SQL-PERSONNEL
WHERE PERSNR IN
( SELECT PERSNR
FROM SQL-AUTOMOBILES
WHERE COLOR = 'black' )
...
END-SELECT
For further information, see Select Expressions.
BETWEEN Predicate
scalar-expression [NOT] BETWEEN
scalar-expression AND
scalar-expression
|
A BETWEEN predicate compares a value with a range of
values.
See information on scalar-expression.
DISTINCT Predicate
scalar-expression IS [NOT] DISTINCT FROM
scalar-expression
|
A DISTINCT predicate compares a value with another value
or a set of values with another set of values.
LIKE Predicate
column-reference [NOT]
LIKE
atom
|
A LIKE predicate searches for strings that have a certain
pattern.
See information on
column-reference
and atom.
NULL Predicate
column-reference IS [NOT] NULL
|
A NULL predicate tests for null values.
See information on
column-reference.
IN Predicate
scalar-expression [NOT] IN |
|
subquery
|
|
| (atom) |
An IN predicate compares a value or a set of values with a
collection of values.
See information on
scalar-expression
and atom.
See information on
subquery.
Quantified Predicate
| scalar-expression comparison |
|
ALL
|
|
subquery |
ANY
|
||||
SOME
|
A quantified predicate compares a value or a set of values with a collection of values.
See information on scalar-expression,
comparison,
and subquery.
EXISTS Predicate
EXISTS
subquery
|
An EXISTS predicate tests for the existence of certain
rows.
The EXISTS predicate evaluates to true only if the result
of evaluating the subquery is not
empty; that is, if there exists at least one record (row) in the
FROM table of the subquery
satisfying the search condition of the WHERE clause of this
subquery.
Example of EXISTS:
DEFINE DATA LOCAL
1 #NAME (A20)
END-DEFINE
...
SELECT NAME
INTO #NAME
FROM SQL-PERSONNEL
WHERE EXISTS
( SELECT *
FROM SQL-EMPLOYEES
WHERE PERSNR > 1000
AND NAME < 'L' )
...
END-SELECT
...
See information on
subquery.