Sql server SQL Server中Case语句中的语法错误

以下代码中出现语法错误： 当我遇到一个错误的时候，我就大胆了。我可以使用if-else语句，但我确实想使用case语句。 请帮我纠正错误

**CASE** @policy_type

        WHEN 'car' THEN 
        (Select policy_id,customer_id,policy_duration,requested_policy_amount,Car_Age
          ,Car_Amount
          ,Number_of_Accidents,estimated_car_premium INTO
           #PendingRequest FROM [dbo].[Policy] p join [dbo].[Car_Insurance] c on
          p.policy_type_id=c.policy_type_id and p.approved_policy_amount is Null 
          --And employee_id=@employee_id
          join
          [dbo].[Car_Insurance_Estimate] c_est on car_age >= c_est.min_car_age and car_age <= c_est.max_car_age
          and Car_Amount>=c_est.min_car_amount and Car_Amount<=c_est.max_car_amount and Number_of_Accidents>=c_est.min_accidents 
            and Number_of_Accidents<=c_est.max_accidents)

        **WHEN** 'life' THEN 

        (Select policy_id,customer_id,policy_duration,requested_policy_amount,Age
          ,l.Illness
          ,l.Income
          ,premium_insurance_percentage,amount_insurance_percentage
           INTO
           #PendingRequest from [dbo].[Policy] p join [dbo].[life_Insurance] l on
          p.policy_type_id=l.policy_type_id and p.approved_policy_amount is Null 
          And employee_id=@employee_id
          join
          [dbo].[life_Insurance_Estimate] l_est on age >= l_est.min_age and age <= l_est.max_age
          and income>=l_est.min_income and income<=l_est.max_income and l.illness=l_est.illness)

        when 'home' then 

        (Select policy_id,customer_id,policy_duration,requested_policy_amount,home_Age
          ,home_Amount
          ,h.Area,home_premium_percentage  INTO
           #PendingRequest 
          from [dbo].[Policy] p join [dbo].[home_Insurance] h on
          p.policy_type_id=h.policy_type_id and p.approved_policy_amount is Null 
          And employee_id=@employee_id
          join
          [dbo].[home_Insurance_Estimate] h_est on home_age >= h_est.min_home_age and home_age <= h_est.max_home_age
          and home_Amount>=h_est.min_home_amount and home_Amount<=h_est.max_home_amount and h.Area=h_est.area)


        **END**

---

在这种情况下，使用IF…ELSE会容易得多。但是，如果您坚持使用CASE，那么这可能是一种选择：

DECLARE @SQL varchar(max);
SELECT @SQL=
CASE @policy_type

        WHEN 'car' THEN 
        'Select policy_id,customer_id,policy_duration,requested_policy_amount,Car_Age
          ,Car_Amount
          ,Number_of_Accidents,estimated_car_premium INTO
           #PendingRequest FROM [dbo].[Policy] p join [dbo].[Car_Insurance] c on
          p.policy_type_id=c.policy_type_id and p.approved_policy_amount is Null 
          --And employee_id=@employee_id
          join
          [dbo].[Car_Insurance_Estimate] c_est on car_age >= c_est.min_car_age and car_age <= c_est.max_car_age
          and Car_Amount>=c_est.min_car_amount and Car_Amount<=c_est.max_car_amount and Number_of_Accidents>=c_est.min_accidents 
            and Number_of_Accidents<=c_est.max_accidents'

        WHEN 'life' THEN 

        'Select policy_id,customer_id,policy_duration,requested_policy_amount,Age
          ,l.Illness
          ,l.Income
          ,premium_insurance_percentage,amount_insurance_percentage
           INTO
           #PendingRequest from [dbo].[Policy] p join [dbo].[life_Insurance] l on
          p.policy_type_id=l.policy_type_id and p.approved_policy_amount is Null 
          And employee_id=@employee_id
          join
          [dbo].[life_Insurance_Estimate] l_est on age >= l_est.min_age and age <= l_est.max_age
          and income>=l_est.min_income and income<=l_est.max_income and l.illness=l_est.illness'

        WHEN 'home' THEN 

        'Select policy_id,customer_id,policy_duration,requested_policy_amount,home_Age
          ,home_Amount
          ,h.Area,home_premium_percentage  INTO
           #PendingRequest 
          from [dbo].[Policy] p join [dbo].[home_Insurance] h on
          p.policy_type_id=h.policy_type_id and p.approved_policy_amount is Null 
          And employee_id=@employee_id
          join
          [dbo].[home_Insurance_Estimate] h_est on home_age >= h_est.min_home_age and home_age <= h_est.max_home_age
          and home_Amount>=h_est.min_home_amount and home_Amount<=h_est.max_home_amount and h.Area=h_est.area'

END

EXEC(@SQL);

拉吉

我可以使用if-else语句，但我确实想使用case语句

每当我看到这一点，我都会三思而后行，考虑这是否是一个真正的问题。为什么?

如果必须将其组合为一条语句，则可以将条件放入SELECT语句中，并使用UNION ALL将它们连接起来，其中只有一条语句会实际生成结果

--declare @policy_type varchar(10), @employee_id int
Select policy_id,customer_id,policy_duration,requested_policy_amount,Car_Age
          ,Car_Amount
          ,Number_of_Accidents,estimated_car_premium
INTO #PendingRequest
          FROM [dbo].[Policy] p join [dbo].[Car_Insurance] c on
          p.policy_type_id=c.policy_type_id and p.approved_policy_amount is Null 
          --And employee_id=@employee_id
          join
          [dbo].[Car_Insurance_Estimate] c_est on car_age >= c_est.min_car_age and car_age <= c_est.max_car_age
          and Car_Amount>=c_est.min_car_amount and Car_Amount<=c_est.max_car_amount and Number_of_Accidents>=c_est.min_accidents 
            and Number_of_Accidents<=c_est.max_accidents
AND @policy_type = 'car'
UNION ALL
Select policy_id,customer_id,policy_duration,requested_policy_amount,Age
          ,l.Illness
          ,l.Income
          ,premium_insurance_percentage,amount_insurance_percentage
          from [dbo].[Policy] p join [dbo].[life_Insurance] l on
          p.policy_type_id=l.policy_type_id and p.approved_policy_amount is Null 
          And employee_id=@employee_id
          join
          [dbo].[life_Insurance_Estimate] l_est on age >= l_est.min_age and age <= l_est.max_age
          and income>=l_est.min_income and income<=l_est.max_income and l.illness=l_est.illness
AND @policy_type = 'life'
UNION ALL
Select policy_id,customer_id,policy_duration,requested_policy_amount,home_Age
          ,home_Amount
          ,h.Area,home_premium_percentage 
          from [dbo].[Policy] p join [dbo].[home_Insurance] h on
          p.policy_type_id=h.policy_type_id and p.approved_policy_amount is Null 
          And employee_id=@employee_id
          join
          [dbo].[home_Insurance_Estimate] h_est on home_age >= h_est.min_home_age and home_age <= h_est.max_home_age
          and home_Amount>=h_est.min_home_amount and home_Amount<=h_est.max_home_amount and h.Area=h_est.area
AND @policy_type = 'home';

---

可以使用if语句代替case

if @policy_type = 'Car'
BEGIN
     Query1
END 
ELSE IF (@policy_type = 'life')
BEGIN
    Query2
END

---

因此，SQL Server中的每个位置都可以访问您的表，CASE/WHEN/THEN只能用于返回单个值，而不是返回/执行整个代码块，替换CASE..WHEN..THEN语句为if@policy_type='care'..else if@policy_type='life'..else如果@policy_type='home'..您还需要创建临时值正在使用create table PendingRequest创建表。。。并在表格中填入insert into PendingRequest select。。。。不可能有多个选择。。。进入在同一批中。IF是一个语句。CASE是一个表达式-它计算一个值。使用此解决方案，只能在动态执行的范围内访问临时表。在创建后，任何应该使用它的操作都必须是动态SQL的一部分。这只是为了提供一个替代解决方案的想法，以解决无法使用基于参数值的代码块执行用例的问题。当然，可能需要先声明临时表并进行填充。很抱歉，这些解决方案都不起作用。无论我使用什么，它都会在CASE或WHEN附近给我一个语法错误。我想我可以很容易地执行一个案例陈述，但这需要很长时间。我的答案不包含：

if @policy_type = 'Car'
BEGIN
     Query1
END 
ELSE IF (@policy_type = 'life')
BEGIN
    Query2
END