Question

为可能有多个结果的select语句的结果创建别名的最佳方法是什么？我尝试过使用Case语句以及If，Then，Else语句，但我在所有实例中都会遇到语法错误。

我的基本代码如下：

Select e.emp_id as 'EmpId'
,pe.name AS 'Goal Plan Name'
,p.id
,(select top 1 (g.statusid) as 'Status' from goals g
inner join goalassignments ga ON ga.goalid = g.id AND g.typeid IN (1,3,5)
where ga.planid = p.id) 

from plans p  
inner join periods (nolock) AS pe on pe.id = p.periodid 
inner join vgr_emp (nolock) AS e on p.empid = e.emp_id

如果g.statusid = 1那么我希望它显示为“待定” 如果g.statusid = 2那么我希望它显示为“已分配” 但是，有些将为空白，并在列中呈现“Null”。我希望这些价值观能说“没有计划”。

案例陈述是最佳还是if陈述？每一个我尝试我得到语法错误。任何帮助将不胜感激。

Answer 1

是案例陈述适合您的要求。

尝试以下：

Select e.emp_id as 'EmpId'
,pe.name AS 'Goal Plan Name'
,p.id
,(select top 1 (case when g.statusid=1 then 'Pending' when g.statusid=2 then 'Assigned' when  g.statusid is null then 'No Plan' end) status
from goals g
inner join goalassignments ga ON ga.goalid = g.id AND g.typeid IN (1,3,5)
where ga.planid = p.id) Status
from plans p  
inner join periods (nolock) AS pe on pe.id = p.periodid 
inner join vgr_emp (nolock) AS e on p.empid = e.emp_id

修改

当您告诉我们您的完整标准时，您可以尝试以下方法：

Select e.emp_id as 'EmpId' ,pe.name AS 'Goal Plan Name' ,p.id ,ISNULL((select top 1 (case when g.statusid=1 then 'Pending' when g.statusid=2 then 'Assigned' end) status from goals g inner join goalassignments ga ON ga.goalid = g.id AND g.typeid IN (1,3,5) where ga.planid = p.id),'No Plan') Status from plans p inner join periods (nolock) AS pe on pe.id = p.periodid inner join vgr_emp (nolock) AS e on p.empid = e.emp_id

Answer 2

在mysql中你可以做这样的事情

select concat(if(g.statusid = 1, 'Pending', ''), if(g.statusid = 2, 'Assigned', ''), if(g.statusid is NULL, 'NoPlan', '')), 
e.emp_id as 'EmpId'
,pe.name AS 'Goal Plan Name' ,p.id
    ,(select top 1 (g.statusid) as 'Status' from goals g
    inner join goalassignments ga ON ga.goalid = g.id AND g.typeid IN (1,3,5)
    where ga.planid = p.id) 
from plans p  
inner join periods (nolock) AS pe on pe.id = p.periodid 
inner join vgr_emp (nolock) AS e on p.empid = e.emp_id

mysql flow control

在条件语句中包装Select语句

2 个答案: