批量更新表时,update一个表的列时,需要依赖另外的表,这种依赖可以是where条件子句,也可以要update的field的值依赖另外的表 通常有两种做法 1.使用存储过程 2.在程序代码里逐条循环执行 这里给出一种更高效、简洁的做法,批量更新SQL ,一句SQL就可以替代麻烦的循环过程,有MS SQLServer、Oracle、DB2下的写法 --关键点:t4和t1是同一个table,primary key肯定也是同一个, --并以它进行关联,这样在 select语句里即可引用到要update的表的fields UPDATE Table1 AS t1 SET (Field1,Field2) = (SELECT Field21, Field22 FROM Table2 t2 INNER JOIN Table3 t3 ON t3.Field31 = t2.Field23 INNER JOIN Table4 t4 ON t3.Field32 = t4.Filed41 WHERE t2.Field24 >= '' AND t1.fId = t4.fId); ----------------------------MS SQLServer --------------------------------------
UPDATE t1 SET Field1 = Field21, Field2 = Field22 FROM Table2 t2 INNER JOIN Table3 t3 ON t3.Field31 = t2.Field23 INNER JOIN Table4 t4 ON t3.Field32 = t4.Filed41 WHERE ((t2.Field24 >= '') AND t1.fId = t4.fId); ----------------------------Oracle --------------------------------------------
UPDATE Table1 t1 SET (Field1,Field2) = (SELECT Field21, Field22 FROM Table2 t2 INNER JOIN Table3 t3 ON t3.Field31 = t2.Field23 INNER JOIN Table4 t4 ON t3.Field32 = t4.Filed41 WHERE ((t2.Field24 >= '') AND t1.fId = t4.fId)) WHERE EXISTS (SELECT Field21, Field22 FROM Table2 t2 INNER JOIN Table3 t3 ON t3.Field31 = t2.Field23 INNER JOIN Table4 t4 ON t3.Field32 = t4.Filed41 WHERE ((t2.Field24 >= '') AND t1.fId = t4.fId)); ---------------------------------DB2 ------------------------------------------
UPDATE Table1 AS t1 SET (Field1,Field2) = (SELECT Field21, Field22 FROM Table2 t2 INNER JOIN Table3 t3 ON t3.Field31 = t2.Field23 INNER JOIN Table4 t4 ON t3.Field32 = t4.Filed41 WHERE ((t2.Field24 >= '') AND t1.fId = t4.fId)) WHERE EXISTS (SELECT Field21, Field22 FROM Table2 t2 INNER JOIN Table3 t3 ON t3.Field31 = t2.Field23 INNER JOIN Table4 t4 ON t3.Field32 = t4.Filed41 WHERE ((t2.Field24 >= '') AND t1.fId = t4.fId));