sql - oracle查询嵌套选择使用案例

Question

我有（2）个案例陈述：

SELECT CASE WHEN EXISTS
                   ( SELECT *
                     FROM MYTABLE_A
                     WHERE timestamp = to_char(sysdate-1, 'yyyymmdd') || '0000'
                   )
            THEN 0
            ELSE 1
       END AS FLAG_MYTABLE_A
from DUAL;
SELECT CASE WHEN EXISTS
                   ( SELECT *, timestamp
                     FROM MYTABLE_B
                     WHERE
                     timestamp = to_char(sysdate-1, 'yyyymmdd') || '0000'
                   )                       )
            THEN 0
            ELSE 1
       END AS FLAG_MYTABLE_B
from DUAL;

结果：

FLAG_MYTABLE_A
--------------
             0

FLAG_MYTABLE_B
--------------
         1

我需要帮助构建此查询，以便显示以下结果。

MYTABLENAME       MYFLAG
-----------       ------
MYTABLE_A              0
MYTABLE_B              1

我在看嵌套选择吗？有人可以告诉我如何设置吗？

Answer 1

您可以使用UNION ALL：

SELECT 'MYTABLE_A' AS MYTABLENAME, CASE WHEN EXISTS
                   ( SELECT *
                     FROM MYTABLE_A
                     WHERE timestamp = to_char(sysdate-1, 'yyyymmdd') || '0000'
                   )
            THEN 0
            ELSE 1
       END AS FLAG_MYTABLE_A
from DUAL
UNION ALL
SELECT 'MYTABLE_B' AS MYTABLENAME, CASE WHEN EXISTS
                   ( SELECT *, timestamp
                     FROM MYTABLE_B
                     WHERE
                     timestamp = to_char(sysdate-1, 'yyyymmdd') || '0000'
                   )                       )
            THEN 0
            ELSE 1
       END AS FLAG_MYTABLE_B
from DUAL;

Answer 2

您可以执行以下操作：

SELECT "MYTABLE_A", CASE ... END AS "MYFLAG" FROM DUAL
UNION
SELECT "MYTABLE_B", CASE ... END AS "MYFLAG" FROM DUAL