mysql - 错误 : argument of AND must be type boolean, 未输入文本

Question

我对下面的查询感到困惑，请问它出了什么问题？

SELECT * FROM my_table 
WHERE 
    col_A <> 'Hello'
    AND col_B <> 'Holla'
    AND col_B <> 'Bonjour'

    AND (CASE WHEN col_c = 6 AND Language_col = 'Fr'THEN 'Français'
       WHEN col_c  = 9  AND Language_col = 'Fr'THEN 'Français'        
       WHEN col_c  = 12 AND Language_col = 'Eng' THEN 'English'
       WHEN col_c  = 4 AND Language_col = 'US' THEN 'Engish'
       ELSE Language END)

order by Date_col  

我收到此类错误:

ERROR: argument of AND must be type boolean, not type text

Answer 1

如果您想要一个新列，则 case 表达式需要进入 select，而不是 where:

SELECT t.*,        
       (CASE WHEN col_c = 6 AND Language_col = 'Fr' THEN 'Français'
             WHEN col_c = 9 AND Language_col = 'Fr' THEN 'Français'        
             WHEN col_c = 12 AND Language_col = 'Eng' THEN 'English'
             WHEN col_c = 4 AND Language_col = 'US' THEN 'English'
             ELSE Language
        END)
FROM my_table t
WHERE col_A <> 'Hello' AND
      col_B NOT IN ( 'Holla', 'Bonjour' )
ORDER BY Date_col ;