动态WHERE子句

Question

我有分组选择的例子：

SELECT cod, value, type 
FROM table
GROUP BY cod, value, type

我得到了结果：

cod | value | type
1   | 1000  | A
1   | 570   | B
2   | 2000  | A
3   | 1500  | A
3   | 200   | B

但只有cod = 1才能从type = A返回值。期望的结果：

cod | value | type
1   | 1000  | A
2   | 2000  | A
3   | 1500  | A
3   | 200   | B

我认为CASE中的WHERE声明但有限制但无效。我怎么能这样做？

WHERE CASE WHEN cod = 1 THEN type = 'A' END 

Answer 1

你在这里：

SELECT cod, value, type 
FROM table
WHERE cod != 1 OR type='A'
GROUP BY cod, value, type

Answer 2

WHERE Type = CASE WHEN cod = 1 THEN 'A' else Type END 

Answer 3

另一个不错的选择 - 不是这里最好的方式，而是一个有用的选择。

SELECT cod, value, type 
FROM table
GROUP BY cod, value, type

EXCEPT

SELECT cod, value, type 
FROM table
WHERE cod = 1 AND type <> 'A'
GROUP BY cod, value, type