选择查询的SQL更新查询

我有下面的查询来列出两个表的雇员

我需要将a.staffdiscountstartdate更新为“20100428”，如何为此重写以下查询

select 
    a.employeeid,
    b.employeeid 
from 
    tblEmployees a
        left join
    tblCards b 
        on
            a.employeeid=b.employeeid 
where 
    GroupStartDate < '20100301' 
and 
    StaffDiscountStartDate > '20100428' 
and 
    datediff(day,groupstartdate,staffdiscountstartdate)>1 
and
    b.employeeid is null

---

应该能够做到：

UPDATE a
SET a.staffdiscountstartdate = '20100428'
from tblEmployees a
    left join tblCards b on a.employeeid=b.employeeid 
where GroupStartDate < '20100301' 
and StaffDiscountStartDate > '20100428' 
and datediff(day,groupstartdate,staffdiscountstartdate)>1 
and b.employeeid is null

仅限MS SQL。其他SQL版本不支持此语法。

有两种方法

一:

二:

两者都可以

update
    tblEmployees
set
    staffdiscountstartdate = '20100428'
where
    employeeid in (
    select 
        a.employeeid
    from 
        tblEmployees a
            left join
        tblCards b 
            on
                a.employeeid=b.employeeid 
    where 
        GroupStartDate < '20100301' 
    and 
        StaffDiscountStartDate > '20100428' 
    and 
        datediff(day,groupstartdate,staffdiscountstartdate)>1 
    and
        b.employeeid is null
    )

---

我添加了一个额外的where子句，作为who需要更新该值（如果该值已经正确存在的话）。我还通过在一行上注释语句的select和column list部分，演示了如何将select用作更新的一部分。这有助于您在运行更新之前查看是否有正确的记录，我认为这样可以更轻松地查看如何将选择状态转换为更新。

+1第一部分与我现在删除的解决方案相同。。。该死的我的慢手指。。。

update a
set a.staffdiscountstartdate = '20100428' 
from tblEmployees a
    left join
tblCards b 
    on
        a.employeeid=b.employeeid 
where 
    GroupStartDate < '20100301' 
and 
    StaffDiscountStartDate > '20100428' 
and 
    datediff(day,groupstartdate,staffdiscountstartdate)>1 
and
    b.employeeid is null

update
    tblEmployees
set
    staffdiscountstartdate = '20100428'
where
    employeeid in (
    select 
        a.employeeid
    from 
        tblEmployees a
            left join
        tblCards b 
            on
                a.employeeid=b.employeeid 
    where 
        GroupStartDate < '20100301' 
    and 
        StaffDiscountStartDate > '20100428' 
    and 
        datediff(day,groupstartdate,staffdiscountstartdate)>1 
    and
        b.employeeid is null
    )

Update a
Set  staffdiscountstartdate = '20100428' 
--select  a.employeeid,  b.employeeid  
from  
    tblEmployees a 
        left join 
    tblCards b  
        on 
            a.employeeid=b.employeeid  
where  
    GroupStartDate < '20100301'  
and  
    StaffDiscountStartDate > '20100428'  
and  
    datediff(day,groupstartdate,staffdiscountstartdate)>1  
and 
    b.employeeid is null 
and 
    a. staffdiscountstartdate <> '20100428'