From: Heikki Linnakangas <hlinnakangas@vmware.com>
To: Sameer Thakur <samthakur74@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Predicate information in EXPLAIN Command
Date: Tue, 14 May 2013 12:29:51 +0300
Message-ID: <5192040F.8060502@vmware.com> (raw)
In-Reply-To: <CABzZFEuTtFiODQ+9AEDBZVXkxVKa5f8+QaNtUBikWN-F0hC57Q@mail.gmail.com>
References: <CABzZFEuTtFiODQ+9AEDBZVXkxVKa5f8+QaNtUBikWN-F0hC57Q@mail.gmail.com>
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On 14.05.2013 12:23, Sameer Thakur wrote:
> Hello,
> I am trying to find predicate information for a given SQL query plan as
> provided by Oracle using DBMS_XPLAN. I am looking at the EXPLAIN command
> for getting this query plan information, with no luck so far.
>
> Does the EXPLAIN command provide predicate information?
Sure. For example,
postgres=# explain select * from a where id = 123;
QUERY PLAN
---------------------------------------------------
Seq Scan on a (cost=0.00..40.00 rows=12 width=4)
Filter: (id = 123)
(2 rows)
The predicate is right there on the Filter line. Likewise for a join:
postgres=# explain select * from a, b where a.id = b.id;
QUERY PLAN
-----------------------------------------------------------------
Hash Join (cost=64.00..134.00 rows=2400 width=8)
Hash Cond: (a.id = b.id)
-> Seq Scan on a (cost=0.00..34.00 rows=2400 width=4)
-> Hash (cost=34.00..34.00 rows=2400 width=4)
-> Seq Scan on b (cost=0.00..34.00 rows=2400 width=4)
(5 rows)
The join predicate is on the Hash Cond line.
- Heikki
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To: pgsql-performance@postgresql.org
Cc: hlinnakangas@vmware.com, samthakur74@gmail.com
Subject: Re: Predicate information in EXPLAIN Command
In-Reply-To: <5192040F.8060502@vmware.com>
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