Takanobu Kawabe schrieb:
> Hello, my name is Takanobu Kawabe. こんいちわ孝信さん：） > I have some questions about left join SQL statement. > > I want to join some tables, and using left join statement . > > the system is the following. I use two machines. > > I created the same databases and tables on both machines. > > OS ： Debian Linux the newest stable 3.1 > Server ： Apache 2.0 > MySQL ： 5.0.20 > PHP ： 5.1.4 > > OS ： WindowsXP > Server ： Apache2.0 > MySQL ： 5.0.19 > PHP ： 5.1.2 > > > > And I considered the following SQL statement to select some columns from > some tables using left join. > > > ---------------------------------------------------------------------------- > SELECT > `MST`.`no`, > `MST`.`denhyono`, > `GUS`.`TANI` AS `GUS`, > `SUIDO`.`TANI` AS `SUIDO`, > `DENKI`.`TANI` AS `DENKI`, > `SYOKUIN1`.`SYOKUINNAME` AS `SYOKUIN1`, > `SYOKUIN2`.`SYOKUINNAME` AS `SYOKUIN2`, > `TANTOSYA`.`TANTOSYANAME` AS `TANTOSYA` > FROM > `MST` > Left Join `TANIMST` AS `GUS` ON `MST`.`GUSno` = `GUS`.`no` > Left Join `TANIMST` AS `SUIDO` ON `MST`.`SUIDOno` = `SUIDO`.`no` > Left Join `TANIMST` AS `DENKI` ON `MST`.`DENKIno` = `DENKI`.`no` > Left Join `SYOKUINMST` AS `SYOKUIN1` ON `MST`.`SYOKUINno1` = `SYOKUIN1`.`no` > Left Join `SYOKUINMST` AS `SYOKUIN2` ON `MST`.`SYOKUINno2` = `SYOKUIN2`.`no` > Left Join `SYOKUINMST` AS `TANTOSYA` ON `MST`.`TANTOSYAno` = > `TANTOSYA`.`no`; > > --------------------------------------------------------------------------------- > I tried this statement without error. > > But Ihave some questions. > > > 1.How many left join keywords can I use in one SQL statement if > there > are 5000 datas in one table? As much as you like. there are no limitations. > 2. when some customers use this query, can they read this query > exactly? Depends on the MySQL knowledge of your customer. But when they are good in SQL they shouldn't have any problem with it. > 3. Will the above query speed become slowly if there are 5000 > datas in one table? Set indizes. This way your queries will speed up. > Will the processing efficiency improve if I use multiple SQL > statement? Always depends on the process. There are processes where multiple SQL queries come in handy. > 4.Is there any other effective SQL statement I can get better > processing efficiency? The beast way would be to start reading the optimization of MySQL: http://dev.mysql.com/doc/refman/5.0/en/optimization.html Here you get a lot of helpful omtimizations for your queries. それじゃ。 Barry -- Smileys rule (cX.x)C --o(^_^o) Dance for me! ^(^_^)o (o^_^)o o(^_^)^ o(^_^o) -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
