Обсуждение: performance comparison: DISTINCT and GROUP BY

Hi,

We have two different queries:
SELECT name,surname  FROM my_table GROUP BY name;

and
SELECT DISTINCT on(name) name,surname  * FROM my_table;

which gives us the same result.

Do these queries differ by their performances? I mean, which one works 
faster? DISTINCT or GROUP BY?

Best regards.

-- 

Devrim GUNDUZ

devrim@oper.metu.edu.tr            Tel  : (312) 295 9318
devrim.gunduz@linux.org.tr        Faks : (312) 295 9494
    Web : http://devrim.oper.metu.edu.tr    -------------------------------------

Hi Devrim,

You can use the EXPLAIN ANALYZE syntax to find out quite easily.

Chris

----- Original Message ----- 
From: "Devrim GUNDUZ" <devrim@oper.metu.edu.tr>
To: "PostgreSQL Mailing Lists-SQL" <pgsql-sql@postgresql.org>
Sent: Monday, August 19, 2002 7:22 PM
Subject: [SQL] performance comparison: DISTINCT and GROUP BY


> 
> Hi,
> 
> We have two different queries:
> 
>  SELECT name,surname  FROM my_table GROUP BY name;
> 
> and
> 
>  SELECT DISTINCT on(name) name,surname  * FROM my_table;
> 
> which gives us the same result.
> 
> Do these queries differ by their performances? I mean, which one works 
> faster? DISTINCT or GROUP BY?
> 
> Best regards.
> 
> -- 
> 
> Devrim GUNDUZ
> 
> devrim@oper.metu.edu.tr Tel  : (312) 295 9318
> devrim.gunduz@linux.org.tr Faks : (312) 295 9494
> 
> Web : http://devrim.oper.metu.edu.tr
> -------------------------------------
> 
> 
> ---------------------------(end of broadcast)---------------------------
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