Question

我试图根据另一个表格中投入的价值选择一个表格。说明

SELECT tale0.*,class.*,hamburger.* 
FROM 
    CASE tale0.id=1 
        THEN class 
    END 
        CASE tale0.id=2 
            THEN hamburger

究竟是这样走路,还是有不同的方法?

Answer 1

No, you can t use a CASE statement in the FROM clause. You will need to join in both tables, then pull the field from the relevant table based on the value:

SELECT
    tale0.*,
    CASE WHEN tale0.id = 1 THEN class.Column1 ELSE hamburger.Column1 END as Column1,
    CASE WHEN tale0.id = 1 THEN class.Column2 ELSE hamburger.Column2 END as Column2,
    ...
FROM
    table0, class, hamburger
-- include join conditions

Answer 2

解决这一问题的另一个办法是:

SELECT TALE0.*, CLASS.*, NULL AS HF1, NULL AS HF2, NULL AS HF3
  FROM TALE0
  INNER JOIN CLASS
    ON CLASS.whatever = TALE0.whatever
UNION ALL
SELECT TALE0.*, NULL AS CF1, NULL AS CF2, NULL AS CF3, HAMBURGER.*
  FROM TALE0
  INNER JOIN HAMBURGER
    ON HAMBURGER.whatever = TALE0.whatever

你们需要拥有像你在高频高温地区那样的多高频1、高频2、高频3等田地,并利用高频高频地区而不是高频1、高频2、高频3等的外地名称。同样,CF1,CF2, 等应当由来自CLCS的外地名称取代。

Best of luck.

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