Question

我有两个表，table1和table2。我已经用一些条件编写了查询，如下所示

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'

如果我运行它，条件不起作用。它正在选择表t2.的所有empid。我检查问题是否为t1.enddate is NULL条件。由于enddate列可以是

某个日期
或，null

如果t1.enddate IS NULL和其他条件成功，我需要获得empid。这里留下的类型与每个empid不同。（每位员工只有一行用于年度提交）。有没有其他替代方法可以做到这一点。

Answer 1

如果使用OR

，则总是需要括号

例如：

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'

但也请注意您似乎没有加入表格。始终使用显式ANSI连接语法，以避免从表中创建行的意外笛卡尔积。

如果两个表中都存在empid，请尝试

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'
   )

t2.adddate可能是> now()吗？这看起来很尴尬。

需要帮助postgreSQL查询

2 个答案: