Message-ID: <3E7C22B8.70601@cnlo.ro>
Date: Sat, 22 Mar 2003 10:45:44 +0200
From: Popeanga Marian <pmarian@cnlo.ro>
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To: Rajesh Kumar Mallah <mallah@trade-india.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: SQL help for efficient time handling..
References: <200303221332.33121.mallah@trade-india.com>
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Hello Mallah,

Have you tryed this :

      SELECT  time_id from time_dimension where sql_time=cast(now() as time without time zone);

Your tabel is indexed for a time h:m:s and you should to have a where 
clause with a time value like this index is defined. Other way you will 
have a filter scan.

Rajesh Kumar Mallah wrote:

>Hi everyone,
>
>I have a table time_dimension loaded with 1440 records
>i record for each min in 24 hrs
>
>
>CREATE TABLE general.time_dimension
>(
>        time_id integer not null ,
>        sql_time time(0) without time zone  not null,
>        PRIMARY KEY (time_id),
>        UNIQUE (sql_time)
>);
>
>sample data is like,
>
>tradein_clients=# SELECT * from time_dimension limit 10;
>+---------+----------+
>| time_id | sql_time |
>+---------+----------+
>|       1 | 00:00:00 |
>|       2 | 00:01:00 |
>|       3 | 00:02:00 |
>|       4 | 00:03:00 |
>|       5 | 00:04:00 |
>|       6 | 00:05:00 |
>|       7 | 00:06:00 |
>|       8 | 00:07:00 |
>|       9 | 00:08:00 |
>|      10 | 00:09:00 |
>+---------+----------+
>(10 rows)
>
>To get current_time_id  i use a query like
>SELECT  time_id from time_dimension where sql_time=date_trunc('minute' , cast(now() as time without time zone) );
>
>it works but uses seq_scan
>Seq Scan on time_dimension  (cost=0.00..35.00 rows=5 width=4) (actual time=4.75..8.16 rows=1 loops=1)      
>   Filter: ((sql_time)::interval = date_trunc('minute'::text, ((now())::time without time zone)::interval)) 
> Total runtime: 8.20 msec
>
>whereas a query like
>
>explain analyze SELECT  time_id from time_dimension where sql_time='13:13:13';
>+------------------------------------------------------------------------------------------------------------------------------------------+
>|                                                                QUERY PLAN                                                                |
>+------------------------------------------------------------------------------------------------------------------------------------------+
>| Index Scan using time_dimension_sql_time_key on time_dimension  (cost=0.00..4.82 rows=1 width=4) (actual time=0.03..0.03 rows=0 loops=1) |
>|   Index Cond: (sql_time = '13:13:13'::time without time zone)                                                                            |
>| Total runtime: 0.06 msec
>--------------------------------------------------------------------------------------------------------------------------------------------
>take much less.
>
>can anyone tell be the best way to get time_id from time_dimension for current_time.
>
>any help is appreciated.
>
>Regds
>Mallah.
>
>
>  
>

-- 
Popeanga Marian
DBA Oracle
CNLO Romania