带有Where / Having子句的SQL查询案例

Question

如何对查询应用Where或Having子句？我遇到了Having子句的问题。

DECLARE @dtDate DATE
SET @dtDate = GETDATE();

with EMS as
    (
       select * from ReportingView.WTA where FiscalMonth = DATENAME(MONTH, @dtDate) + ', ' +  DATENAME(YEAR, @dtDate) and ProductGroup = 'AAD'
    )

select 
       [ID]
      ,(CASE 
            WHEN Entitlements <= 0 THEN '0'
            ELSE CAST([Activations] as float) / [Entitlements]
        END) as Utilization 
from EMS
**HAVING  Utilization >= .25**

Answer 1

where和having子句都在查询的末尾。如果你有两个，那么where在having之前。

在你的情况下，你的having不起作用，因为having只与group by一起使用。 having本质上是汇总值的where条款（例如sum，count等）

---

例子：

WHERE

SELECT
    *
FROM
    EMS
WHERE
    Utilization >= 0.25

HAVING

SELECT
    col1, count(*)
FROM
    EMS
GROUP BY
    col1
HAVING
    count(*) > 10

HAVING和WHERE

SELECT
    col1, count(*)
FROM
    EMS
WHERE
    Utilization >= 0.25
GROUP BY
    col1
HAVING
    count(*) > 10

---

编辑：此修改后的查询应该适合您。我不确定为什么你的原始查询使用CTE，但我已经将case逻辑移动到了CTE。

with EMS as
(
    select 
        [ID],
        (
            CASE 
                WHEN Entitlements <= 0 THEN '0'
                ELSE CAST([Activations] as float) / [Entitlements]
            END
        ) as Utilization 
    from
        ReportingView.WTA 
    where
        FiscalMonth = DATENAME(MONTH, @dtDate) + ', ' +  DATENAME(YEAR, @dtDate)
        and ProductGroup = 'AAD'
)
select
    *
from
    EMS
where
    Utilizaiton >= .25

Answer 2

HAVING关键字仅在您使用GROUP BY时使用。你想要的是一个WHERE，但除非你把它包装在子选择中，否则你将无法引用Utilization。