Question

我有下表：

TableA

Category  Code Sub
           AA   CS
           AB   CD
  TK       AS

TableB

Category  Code Sub  Found
  D1       AA   CS    0
           AA   CS    0
  D3            CD    0
  TK       AS         0

我如何使用TableA将TableB更新为以下内容，如果发现整行与TableA中的行匹配，发现的行将等于1？

Category  Code Sub  Found
  D1       AA   CS    0
           AA   CS    1
  D3            CD    0
  TK       AS         1

Answer 1

我会使用exists：

update b
      set b.found = 1
from tableb b
where exists (select 1 
              from tablea a 
              where b.category = a.category and 
                    b.code = a.code and 
                    b.sub = a.sub
             );

Answer 2

您可以使用join：

update b
    set found = 1
    from b join
         a
         on b.category = a.category and b.code = a.code and b.sub = a.sub;

这假定空格为空字符串，而不是NULL。

如果它们是null，则性能可能会受到影响，但是您可以这样做：

update b
    set found = 1
    from b join
         a
         on (b.category = a.category or b.category is null and a.category is null) and
            (b.code = a.code or b.code is null and a.code is null) and
            (b.sub = a.sub or b.sub is null and a.sub is null);

Answer 3

您可以使用以下查询，该查询使用JOIN联接TableA和TableB，并在联接时使用COALESCE处理空值：

UPDATE
        tb
SET
        Found = 1
FROM
        TableB tb
    JOIN
        TableA ta
            ON COALESCE(tb.Category, 0) = COALESCE(ta.Category, 0)
               AND COALESCE(tb.Code, 0) = COALESCE(ta.Code, 0)
               AND COALESCE(tb.Sub, 0) = COALESCE(ta.sub, 0);

比较2个表并根据结果更新一列？

3 个答案: