tsql - T-SQL用单选从表的行中初始化几个变量

Question

我有下表（假设它的名称是“AnswerTable”：

QuestionID Value
100        1
101        2
102        1
103        2
104        1
105        2
...

然后我有几个变量：

DECLARE @Answer1 INT
DECLARE @Answer2 INT
....

我需要像这样从表中检索信息：

SET @Answer1 =(SELECT Value FROM AnswerTable WHERE QuestionID=100)
SET @Answer2 =(SELECT Value FROM AnswerTable WHERE QuestionID=101)
...

我想要做的是只从表中选择一个来初始化变量，因为在我的实际情况下，表非常大并且它与其他表连接，我担心子查询的多次执行不会要高效。

是否有捷径可寻？

Answer 1

一般来说;

SELECT @Answer1 = col1, @Answer2 = col2, ... FROM yourTable

在你的情况下；

SELECT @Answer1 = case QuestionID when 100 then Value Else @Answer1 End, 
       @Answer2 = case QuestionID when 101 then Value Else @Answer2 End
FROM AnswerTable
WHERE QuestionID IN  (100,101)

例如： Sql Fiddle 示例

Answer 2

这有点尴尬，但您可以使用连接来执行此操作。

http://sqlfiddle.com/#!3/e3fe7/4

DECLARE @Answer1 INT
DECLARE @Answer2 INT

SELECT 
  @Answer1 = Question100.Value, 
  @Answer2 = Question101.Value 
FROM 
  AnswerTable AS Question100 
INNER JOIN AnswerTable AS Question101 
  ON Question101.QuestionId = 101 
WHERE Question100.QuestionID=100


select @Answer1, @Answer2