From: Tom Lane <tgl@sss.pgh.pa.us>
To: =?UTF-8?B?0JDQvdC00YDQtdC5INCl0L7Qt9C+0LI=?= <avkhozov@gmail.com>
cc: pgsql-performance@postgresql.org
Subject: Re: Performance issue with castings args of the function
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Comments: In-reply-to =?UTF-8?B?0JDQvdC00YDQtdC5INCl0L7Qt9C+0LI=?=
 <avkhozov@gmail.com>
	message dated "Mon, 02 Jan 2017 19:34:49 +0500"
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Date: Mon, 02 Jan 2017 11:36:20 -0500
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=?UTF-8?B?0JDQvdC00YDQtdC5INCl0L7Qt9C+0LI=?= <avkhozov@gmail.com> writes:
> create table t1 (id serial, str char(32));

> create function f1(line text) returns void as $$
> begin
>   perform * from t1 where str = line;
> end;
> $$ language plpgsql;

This query is specifying a text comparison (text = text operator).
Since the table column isn't text, a char-to-text conversion must
happen at each line.

> create function f2(line char) returns void as $$
> begin
>   perform * from t1 where str = line;
> end;
> $$ language plpgsql;

This query is specifying a char(n) comparison (char = char operator).
No type conversion step needed, so it's faster.

			regards, tom lane


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