MySQL“；及；声明问题

我有2张表（下面的示例）

我想提取

name

、

datein

都相等且

dateout

都为空的数据

我正在使用下面的查询，但得到的是空响应

SELECT name,datein 
FROM aTable 
WHERE (name = 'test' AND dateout IS NULL) AND 
      (SELECT name FROM bTable WHERE name = 'test' AND dateout IS NULL)

有什么我遗漏的吗？

试试这个

  SELECT name,datein,dateout FROM(select * from atable union select * from btable)as tt 
where tt.name ='test' and tt.dateout is null;

试试这个

  SELECT name,datein,dateout FROM(select * from atable union select * from btable)as tt 
where tt.name ='test' and tt.dateout is null;

---

您需要将

EXISTS

添加到查询中：

SELECT t1.name, t1.datein 
FROM aTable AS t1
WHERE (t1.name = 'test' AND t1.dateout IS NULL) AND 
      EXISTS(SELECT name 
             FROM bTable AS t2
             WHERE t2.name = 'test' AND 
                   t2.datein = t1.datein AND
                   t2.dateout IS NULL)

或者，不为

name

字段提供特定值：

SELECT t1.name, t1.datein 
FROM aTable AS t1
WHERE t1.dateout IS NULL AND 
      EXISTS(SELECT name 
             FROM bTable AS t2
             WHERE t2.name = t1.name AND 
                   t2.datein = t1.datein AND
                   t2.dateout IS NULL)

---

您需要将

EXISTS

添加到查询中：

SELECT t1.name, t1.datein 
FROM aTable AS t1
WHERE (t1.name = 'test' AND t1.dateout IS NULL) AND 
      EXISTS(SELECT name 
             FROM bTable AS t2
             WHERE t2.name = 'test' AND 
                   t2.datein = t1.datein AND
                   t2.dateout IS NULL)

或者，不为

name

字段提供特定值：

SELECT t1.name, t1.datein 
FROM aTable AS t1
WHERE t1.dateout IS NULL AND 
      EXISTS(SELECT name 
             FROM bTable AS t2
             WHERE t2.name = t1.name AND 
                   t2.datein = t1.datein AND
                   t2.dateout IS NULL)

---

为什么要试试这个？它改变了什么？它有什么作用？解释你的答案。为什么要尝试这个？它改变了什么？它有什么作用？解释你的答案。