Question

我有三张桌子：

t1.columns: a,c
t2.columns: a,b
t3.columns: b,c,d

现在我想要的是用t3.d更新t1.c.但我不能只使用t1.c = t3.c从t3更新t1。我也必须通过t3.b = t2.b和t1.a = t2.a。

我尝试过这样的事情：

UPDATE table1 t1
   SET t1.c = (select t3.d
               from table2 t2, table3 t3
               where t2.b = t3.b and t1.a = t2.a)                                  
 WHERE EXISTS ( SELECT 1 FROM table2 t2, table3 t3 WHERE t1.c = t3.c and t1.a = t2.a);

此代码生成error-msg：ORA-01427：单行子查询返回多行

Answer 1

如果t1和t2之间或t2和t3之间存在一对多的关系，那么t1中的每一行都会得到很多匹配。如果您知道t3中属于t1中同一行的所有行在d中具有相同的值，那么您可以使用DISTINCT删除（相同的）重复项。

UPDATE table1 t1
   SET t1.c = (select DISTINCT t3.d
               from table2 t2, table3 t3
               where t2.b = t3.b and t1.a = t2.a)                                  
 WHERE EXISTS ( SELECT 1 FROM table2 t2, table3 t3 WHERE t1.c = t3.c and t1.a = t2.a);

Answer 2

您有一个返回多行的子查询。使用rownum只能获得一行：

UPDATE table1 t1
   SET t1.c = (select d
               from (select t3.d
                     from table2 t2 join table3 t3
                          on t2.b = t3.b 
                     where t1.a = t2.a
                    ) t
                where rownum = 1
               )                                
 WHERE EXISTS ( SELECT 1 FROM table2 t2, table3 t3 WHERE t1.c = t3.c and t1.a = t2.a);

Answer 3

很抱歉这个混乱，但我解决了它：

UPDATE table t1
SET t1.c = (select t3.d from table3 t3, table2 t2
                          where t1.a = t2.a and t2.b = t3.b and t3.c = t1.c)
 WHERE EXISTS ( SELECT 1 FROM table1 t1, table2 t2 WHERE t1.a = t2.a and t2.b = t3.b and t3.c = t1.c)

Answer 4

UPDATE table1 t1
   SET t1.c = (select MAX(t3.d)
               from table2 t2, table3 t3
               where t2.b = t3.b and t1.a = t2.a)                                  
 WHERE EXISTS ( SELECT 1 FROM table2 t2, table3 t3 WHERE t1.c = t3.c and t1.a = t2.a);

Oracle SQL相关更新

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