From: Rajesh Kumar Mallah <mallah@trade-india.com>
Organization: Infocom Network Limited
To: pgsql-sql@postgresql.org
Subject: SQL help for efficient time handling..
Date: Sat, 22 Mar 2003 13:32:33 +0530
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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.


-- 
Rajesh Kumar Mallah,
Project Manager (Development)
Infocom Network Limited, New Delhi
phone: +91(11)6152172 (221) (L) ,9811255597 (M)

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