Question

我想从多个相同构造的表中选择，为每一行返回三列的值，其中一列的值由另一个查询找到。例如，执行此操作的低效方法可能是：

Select Film_Title, Main_Actor, Run_Time From Film_Table_1
  Where Film_Title in
       (Select Film_Title
          From Awesome_Films_Table
          Where Film_Year equals "1984")
UNION ALL
Select Film_Title, Main_Actor, Run_Time From Film_Table_2
  Where Film_Title in
       (Select Film_Title
          From Awesome_Films_Table
          Where Film_Year equals "1984")
Select Film_Title, Main_Actor, Run_Time From Film_Table_3
  Where Film_Title in
       (Select Film_Title
          From Awesome_Films_Table
          Where Film_Year equals "1984")
Select Film_Title, Main_Actor, Run_Time From Film_Table_4
  Where Film_Title in
       (Select Film_Title
          From Awesome_Films_Table
          Where Film_Year equals "1984");

实际上，我有很多'Film_Table_＃'可供选择。任何人都可以建议如何更有效地实现这一目标？我认为更换：

Select Film_Title
            From Awesome_Films_Table
            Where Film_Year equals "1984"

我目前在每个Where说明符上都有一个在开始时定义的单个变量可能有帮助，但我不确定如何实现。

Answer 1

Oracle中的类似内容：

equals应该是=
“应该是'

最糟糕的设计是每部电影有一张桌子。理想情况下，在一个集中的表格中，每部电影应该是一行（如果需要，可以去NF））

WITH AFT
  AS (SELECT
           FILM_TITLE TITLE
      FROM
           AWESOME_FILMS_TABLE
      WHERE
           FILM_YEAR = '1984')
SELECT
    FILM_TITLE,
    MAIN_ACTOR,
    RUN_TIME
FROM
    FILM_TABLE_1,
    AFT
WHERE
    FILM_TITLE = TITLE
UNION ALL
SELECT
    FILM_TITLE,
    MAIN_ACTOR,
    RUN_TIME
FROM
    FILM_TABLE_2,
    AFT
WHERE
    FILM_TITLE = TITLE
UNION ALL
SELECT
    FILM_TITLE,
    MAIN_ACTOR,
    RUN_TIME
FROM
    FILM_TABLE_3,
    AFT
WHERE
    FILM_TITLE = TITLE
UNION ALL
SELECT
    FILM_TITLE,
    MAIN_ACTOR,
    RUN_TIME
FROM
    FILM_TABLE_4,
    AFT
WHERE
    FILM_TITLE = TITLE;</li>

从多个表中有效选择，从另一个表中选择的值

1 个答案: