mysql – 在查询中使用联接时出错

我有这个问题：

SELECT * FROM `employee_activities` a
LEFT JOIN `activity` b ON a.activity_code = b.code
LEFT JOIN `employees` c ON a.employee_code = c.code
WHERE b.type = "Design"
AND c.code NOT IN(
    SELECT * FROM `employee_activities` a
        LEFT JOIN `activity` b ON a.activity_code = b.code
        LEFT JOIN `employees` c ON a.employee_code = c.code
        WHERE b.type = "Testing"
)
GROUP BY c.code

我收到此错误：

#1241 - Operand should contain 1 column(s)

我想要让所有至少有一个类型为“设计”活动且没有活动类型为“测试”的员工.

我有一个有效的查询但我希望它可以使用连接.

这有效：

SELECT c.name FROM `employee_activities` a,`activity` b,`employees` c
WHERE a.activity_code = b.code
AND a.employee_code = c.code
AND b.type = "Design"

AND c.code NOT IN(
    SELECT c.code FROM `employee_activities` a,`employees` c
        WHERE a.activity_code = b.code
        AND a.employee_code = c.code
        AND b.type = "Testing"
)
GROUP BY c.code

我在连接的sql上做错了什么？ 最佳答案 对于不在子查询中 – 它应该只包含一列 – 例如

SELECT * FROM `employee_activities` a
LEFT JOIN `activity` b ON a.activity_code = b.code
LEFT JOIN `employees` c ON a.employee_code = c.code
WHERE b.type = "Design"
AND c.code NOT IN(
    SELECT b.employee_code FROM `employee_activities` a
        LEFT JOIN `activity` b ON a.activity_code = b.code
        LEFT JOIN `employees` c ON a.employee_code = c.code
        WHERE b.type = "Testing"
)
GROUP BY c.code

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