Re: TO_CHAR SO SLOW???

On Mon, Jun 23, 2003 at 06:08:19PM -0700, Maksim Likharev wrote:
> Hi,
> I have some SQL function, just regular function selects data by using 4
> joins nothing fancy,
> but one thing pretty noticeable,
> I have to display 3 different columns with same date formatted
> differently,
> here are 3 different snippets:
>
> 1. SELECT t.x,t.y,TO_CHAR(t.dt, 'DD/MM/YYYY')
> FROM ( SELECT x, y, dt FROM .... ) AS t
> ...
> 2. SELECT t.x,t.y,TO_CHAR(t.dt, 'DD/MM/YYYY'), TO_CHAR(t.dt, 'Mon-YYYY')
> FROM ( SELECT x, y, dt FROM .... ) AS t
> ..
> 3. SELECT t.x,t.y,TO_CHAR(t.dt, 'DD/MM/YYYY'), TO_CHAR(t.dt,
> 'Mon-YYYY'), TO_CHAR(t.dt, 'YYYY')
> FROM ( SELECT x, y, dt FROM .... ) AS t
> ...
>
> # 1: 15000 rows, I getting data for 130 sec
> # 2: 15000 rows, I getting data for 160 sec
> # 3: 15000 rows, I getting data for 220 sec
>
> adding different fields into output change query time only marginally
> but adding or removing to_char,
> just heavily knocks performance.
>
> is it TO_CHAR so slow??

I don't think to_char() is so slow. What happen with performance
if you use t.dt without formatting or if try some other function
an example extract()?

SELECT t.x, t.y, t.dt FROM ( SELECT x, y, dt FROM .... ) AS t;

SELECT t.x, t.y, EXTRACT(year from t.dt)
FROM ( SELECT x, y, dt FROM .... ) AS t;

Karel

--
Karel Zak <zakkr(at)zf(dot)jcu(dot)cz>
http://home.zf.jcu.cz/~zakkr/