Description:
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The documentation mentions that PDO::FETCH_COLUMN accepts either a 1-indexed integer or the column name as string. While fixing #44173 I've noticed that both hints are wrong. On PHP 5.3 any string is casted to int (therefore becoming 0) and the parameter is in fact supposed to be 0-indexed.

Note: the proposed fix for #44713 enforces the colno parameter to be integer.

A documentation patch will be available shortly.

Reproduce code:
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var_dump($db->query("SELECT 1 as a, 2 as b", PDO::FETCH_COLUMN, 'b')->fetch());

Expected result:
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string(1) "2"

Actual result:
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string(1) "1"