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- ------------------
- DISTINCT predicate
- ------------------
- Function:
- Specify a test of whether two row values are distinct.
- Author:
- Oleg Loa <[email protected]>
- Dmitry Yemanov <[email protected]>
- Syntax rules:
- <value> IS [NOT] DISTINCT FROM <value>
- Scope:
- DSQL, PSQL
- Example(s):
- 1. SELECT * FROM T1 JOIN T2 ON T1.NAME IS NOT DISTINCT FROM T2.NAME;
- 2. SELECT * FROM T WHERE T.MARK IS DISTINCT FROM 'test'
- Note(s):
- 1. A DISTINCT predicate evaluates very similar to an equality predicate with
- the only difference that two NULL values are considered not distinct. As a result,
- this predicate never evaluates to UNKNOWN truth value (the same as IS [NOT] NULL
- predicate behaves).
- 2. The NOT DISTINCT predicate can be optimized via an index, if exists.
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