sql - 如何显示带有条件的2个表中的值

Question

使用 SQL Server 2000

表1

ID date value

001 23/01/2012 100
002 25/02/2012 200
....

表2

Id date value

001 01/01/2012 200
001 02/01/2012 100
...
001 23/02/2012 200
...
001 31/03/2012 100
002 ....
.....

我想选择table2的值，如果id和日期与table1匹配，那么值将从table1显示

ID 日期值

001 01/01/2012 200
001 02/01/2012 100
...
001 23/02/2012 100 'matching id and date from table1
...
001 31/03/2012 100
002 ....
.....

如何做到这一点。

需要查询帮助

预期输出

Answer 1

SELECT DISTINCT Table2.ID, Table2.date,
            CASE
                WHEN Table1.ID = Table2.ID
                     AND Table1.date = Table2.date THEN Table1.value
                ELSE Table2.value
            END
FROM Table1, Table2

编辑

SELECT n_t.n_ID,
       n_t.n_date,
       n_t.n_value
FROM
  (SELECT Table2.ID AS n_ID,
          Table2.date AS n_date,
          CASE
              WHEN Table1.ID = Table2.ID THEN CASE
                                                  WHEN Table1.date = Table2.date THEN Table1.value
                                                  ELSE Table2.value
                                              END
          END AS n_value
   FROM Table1,
        Table2) AS n_t
WHERE n_t.n_value IS NOT NULL