Question

我正在处理复杂的问题，但我会将其简化为此问题。

我有两张桌子

A [ID, column1, column2, column3]
B [ID, column1, column2, column3, column4]
C [ID, column1, column2,column3]

我正在使用此查询创建另一个第三个表。

UPDATE C 
  set column1=t.firstTab, column2=t.secondTab, column3=t.thirdTab 
  from (select A.column1 as firstTab, B.column2 as secTab, 
              (A.column1 + B.column2) thirdTab 
        from A, B limit 1; ) as t ;

我得到了：更新0

当我运行此查询时：

select A.column1 as firstTab, B.column2 as secTab, (A.column1 + B.column2) thirdTab 
            from A, B limit 1;

我得到了结果。

Answer 1

根据评论，这将更新投影的第一行（未指定顺序）的所有C行：

UPDATE C
  set column1=t.firstTab, column2=t.secTab, column3=t.thirdTab 
  FROM 
    (select A.column1 as firstTab, B.column2 as secTab, 
            (A.column1 + B.column2) thirdTab 
     from A, B limit 1) as t;

SqlFiddle here

如果您只想使用投影的第一行更新一行C，并且C.ID是主键：

UPDATE C 
  set column1=t.firstTab, column2=t.secondTab, column3=t.thirdTab 
  from
  (select A.column1 as firstTab, B.column2 as secondTab, 
              (A.column1 + B.column2) thirdTab 
        from A, B limit 1) as t 
  WHERE C.ID IN (SELECT ID from C LIMIT 1);

但是，如果您在C上没有主键，则可以使用CTID system column：

UPDATE C 
  set column1=t.firstTab, column2=t.secondTab, column3=t.thirdTab 
  from
  (select A.column1 as firstTab, B.column2 as secondTab, 
              (A.column1 + B.column2) thirdTab 
        from A, B limit 1) as t 
  WHERE CTID IN (SELECT CTID from C LIMIT 1);

Updated Fiddle here

来自其他表的SQL UPDATE

1 个答案: