Re: A fairly obvious optimization?
| От | Zeugswetter Andreas SB SD |
|---|---|
| Тема | Re: A fairly obvious optimization? |
| Дата | |
| Msg-id | 46C15C39FEB2C44BA555E356FBCD6FA4961DCF@m0114.s-mxs.net обсуждение исходный текст |
| Ответ на | A fairly obvious optimization? ("Dann Corbit" <DCorbit@connx.com>) |
| Ответы |
Re: A fairly obvious optimization?
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| Список | pgsql-hackers |
> The select(min) and select(max) took as long as the table scan to find > the count. It seems logical if a btree type index is available (such > as pk_cnx_ds_sis_bill_detl_tb) where the most significant bit of the > index is the column requested, it should be little more than a seek > first or seek last in the btree. Obviously, it won't work with a hashed > index (which is neither here nor there). In the meantime you can use: select extr_stu_id from cnx_ds_sis_bill_detl_tb order by 1 desc limit 1; -- max select extr_stu_id from cnx_ds_sis_bill_detl_tb order by 1 asc limit 1; -- min I guess that is the reason why nobody felt really motivated to implement this optimization. Besides these statements are more powerful, since they can fetch other columns from this min/max row. The down side is, that this syntax varies across db vendors, but most (all?) have a corresponding feature nowadays. select first 1 select top 1 ... This is actually becoming a FAQ :-) Andreas
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