Peter Eisentraut wrote:
D'Arcy J.M. Cain wrote:
SELECT * FROM table WHERE column IS NULL;
SELECT * FROM table WHERE column = NULL;
The latter violates the SQL spec and is not allowed by PostgreSQL
without setting a special flag.
It doesn't violate any spec and it's certainly allowed by PostgreSQL
without any flags. It's just that the result is not what some people
expect.
"= NULL" violates the SQL-92 Specification. Relevant section posted below.
Additionally *none of the example code* in the SQL-92 specification
document uses the expression "WHERE #value# = NULL"
*All* the example code in the specification use the expression as:
"WHERE #value# IS NULL"
8.6 <null predicate>
Function
Specify a test for a null value.
Format
<null predicate> ::= <row value constructor> IS [ NOT ] NULL
Syntax Rules
None.
Access Rules
None.
General Rules
1) Let R be the value of the <row value constructor>.
2) If all the values in R are the null value, then "R IS NULL" is
true; otherwise, it is false.
3) If none of the values in R are the null value, then "R IS NOT
NULL" is true; otherwise, it is false.
Note: For all R, "R IS NOT NULL" has the same result as "NOT
R IS NULL" if and only if R is of degree 1. Table 12, "<null
predicate> semantics", specifies this behavior.
________________Table_12-<null_predicate>_semantics________________
R IS R IS NOT NOT R IS NOT R IS NOT
_Expression_______NULL____NULL__________NULL__________NULL_________
| degree 1: null | true | false | false | true |
| | | | | |
| degree 1: not | false | true | true | false |
null
| degree > 1: | true | false | false | true |
| all null | | | | |
| | | | | |
| degree > 1: | false | false | true | true |
| some null | | | | |
| | | | | |
| degree > 1: | false | true | true | false |
|_none_null______|_______|_____________|____________|______________|
| | | | | |
|Leveling Rules | | | | |
| | | | | |
218 Database Language SQL
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