Peter Eisentraut <peter_e@gmx.net> writes:
> That is, why can't you write
> SELECT 1 IN ( ARRAY[1, 2, 3] );
> when you can write
> SELECT 1 = ANY ( ARRAY[1, 2, 3] );
> ?

The two syntaxes are in fact *not* equivalent according to SQL92.
= ANY derives from

<quantified comparison predicate> ::=
<row value constructor> <comp op> <quantifier> <table subquery>

<quantifier> ::= <all> | <some>

<all> ::= ALL

<some> ::= SOME | ANY

(notice the RHS *must* be a <table subquery>) whereas IN comes from

<in predicate> ::=
<row value constructor>
[ NOT ] IN <in predicate value>

<in predicate value> ::=
<table subquery>
| <left paren> <in value list> <right paren>

<in value list> ::=
<value expression> { <comma> <value expression> }...

The form "expr = ANY (non-query-expr)" is therefore a spec extension,
which we are free to define as we wish, and we defined it to be a
scalar-vs-array-elements comparison. But I don't see any way that we
can interpret "expr IN (other-expr)" as anything except a variant
spelling for a simple equality test.

regards, tom lane

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