Question

当设置特定值时，是否只能按特定行分组？

即。我有下表：

USERNO  |   FIRSTNAME   |   NAME    |   CUSTOMER    |   YEAR
1       |   Jon         |   Snow    |   0           |   2014
2       |   Williams    |   Spear   |   1           |   2015
1       |   John        |   Snow    |   1           |   2015
3       |   Sam         |   Wells   |   0           |   2014
3       |   Sam         |   Wells   |   0           |   2013

当CUSTOMER为1时，它应按USERNO分组。所以我想要以下结果：

USERNO  |   FIRSTNAME   |   NAME    |   CUSTOMER    |   YEAR
1       |   Jon         |   Snow    |   1           |   2014
2       |   Williams    |   Spear   |   1           |   2015
3       |   Sam         |   Wells   |   0           |   2014
3       |   Sam         |   Wells   |   0           |   2013

这可能吗？

提前致谢！

Answer 1

您可以使用UNION获取此类结果：

SELECT *
FROM tablename
WHERE CUSTOMER != 1
UNION 
SELECT *
FROM tablename
WHERE CUSTOMER = 1
GROUP BY USERNO;

或者你也可以使用CASE，但是当条件不满足时你必须指定ELSE部分来分组记录：

SELECT *
FROM tablename
GROUP BY CASE WHEN CUSTOMER  = 1 THEN USERNO ELSE columnname END;

如果您希望将结果分组为GROUP_CONCAT分隔列表，则可以使用COMMA这样的结果：

SELECT 
  GROUP_CONCAT(DISTINCT CAST(USERNO) AS CHAR),
  GROUP_CONCAT(DISTINCT CAST(FIRSTNAME) AS CHAR),
  GROUP_CONCAT(DISTINCT CAST(NAME) AS CHAR),
  CUSTOMER,
  GROUP_CONCAT(DISTINCT CAST(YEAR) AS CHAR)
FROM tablename
GROUP BY CUSTOMER;

MySQL组通过调节

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