Re: How to find out about index
От | Shridhar Daithankar |
---|---|
Тема | Re: How to find out about index |
Дата | |
Msg-id | 3DA2D99F.32643.143B580C@localhost обсуждение исходный текст |
Ответ на | Re: How to find out about index (Savita <savita@india.hp.com>) |
Список | pgsql-general |
On 8 Oct 2002 at 12:22, Savita wrote: > > Hi, > What does the row indicate in the NOTICE: QUERY PLAN: It's what it says. What follows is a query plan. A notice is used to indicate warning style stuff to users but can be anything really. I'ts like a fprintf(stderr.. > I am getting diff-2 values which is not same as the actual row present in the > table. > For example > with select statement > TESTDATA=# explain select * from os_customer_master; > NOTICE: QUERY PLAN: > Seq Scan on os_customer_master (cost=0.00..20.00 rows=1000 width=112) > ============================================================================== > with where clause > TESTDATA=# explain select * from os_customer_master where > outsourcer_legacy_custo > mer_id='66084'; > NOTICE: QUERY PLAN: > Seq Scan on os_customer_master (cost=0.00..22.50 rows=10 width=112) > ================================================================================ Well the qeury plan is changed because of where condition. Relying upon last updated statistics, planner know how many rows are in a relation and attempts to project cost and other factor for a query. Obviously a where condition changes this estimation.. > = > After creating index on outsourcer_legacy_custo > mer_id > TESTDATA=# explain select * from os_customer_master where > outsourcer_legacy_custo > mer_id='66084'; > NOTICE: QUERY PLAN: > Index Scan using cust_1 on os_customer_master (cost=0.00..12.22 rows=11 > width=112) It has decided that an indexed scan would be better rather than a sequential scan. Rows indicates expected number of rows but this is just an approximation. Width is probably width of tuple returned. It would/should vary depending upon what fields you select. But not sure of this width business.. HTH Bye Shridhar -- pension: A federally insured chain letter.
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