需要帮助在PostgreSQL查询

Question

我有两个表，table1和table2。我已经写了查询一些条件如下

Select t2.employee_id, 
t2.adddate, 
t2.previousaleave 
from table2 as t2, table1 as t1 
WHERE t1.enddate IS NULL 
    OR t1.enddate>t2.adddate 
    AND t2.adddate<=now() 
    AND t2.leavetype='annualleave' 

如果我运行此，条件不working.It是选择t2.?I检查，这个问题是与t1.enddate is NULL条件表的所有empids 。由于enddate列可以是，

• 一些日期
• 或null

我需要，如果t1.enddate IS NULL和其他条件成功获得EMPID。这里离开类型与每个empid都有区别。 （每位员工只有一排年度飞行）。有没有其他的方法可以做到这一点。

Answer 1

你总是如使用或

例如需要括号：

Select t2.employee_id,t2.adddate,t2.previousaleave 
from table2 as t2 
Inner join table1 as t1 ON ............. ????? 
WHERE (t1.enddate IS NULL OR t1.enddate>t2.adddate AND t2.adddate<=now()) 
AND t2.leavetype='annualleave' 

还要注意你似乎没有加入的表。始终使用明确的ANSI连接语法来避免从表中创建行的意外笛卡尔积。

如果EMPID存在于两个表尝试

Select t2.employee_id,t2.adddate,t2.previousaleave 
from table2 as t2 
Inner join table1 as t1 ON t2.empid = t1.empid 
WHERE (t1.enddate IS NULL OR t1.enddate>t2.adddate AND t2.adddate<=now()) 
AND t2.leavetype='annualleave' 

Answer 2

SELECT t2.employee_id, t2.adddate, t2.previousaleave 
FROM table2 AS t2 
INNER JOIN table1 as t1 
    ON (
    (t1.enddate IS NULL OR t1.enddate > t2.adddate) 
    AND t2.adddate <= now() 
    AND t2.leavetype = 'annualleave' 
    ) 

是否有可能为t2.adddate是> now()？这看起来很尴尬。