/* 创建表CREATE TABLE TB
(
[t1] [int] IDENTITY (1, 1) NOT NULL ,
[t2] [nvarchar] (100)
)
INSERT INTO TB
--插入字段的公式
SELECT 'case when 1=1 then 1 else 0 end '
INSERT INTO TB
SELECT 'case when ''+@C+'' =1 then ''A'' ELSE ''B'' END 'SELECT * FROM TB
*/
DECLARE @a AS INTEGER,
@b AS INTEGER,
@C AS VARCHAR(100),
@D AS VARCHAR(100),
@Sql AS VARCHAR(1000)
BEGIN
SET @a=1
SET @b=3
-- SELECT @C='case when 1=1 then 1 else 0 end '
-- SELECT @d= 'case when '+@C+' =1 then ''A'' ELSE ''B''END '
SELECT @C=t2 FROM TB WHERE t1=1
SELECT @d=t2 FROM TB WHERE t1=3
print( 'SELECT '+@C+' A , '+@d+'' B)
-- exec( 'SELECT '+@C+', '+@d+'')
END
实现这个查询公式,如何不用嵌套把结果查询出来,希望能在一个查询里简单实现
@D=case when t1=3 then t2 else null end
from tb
where t1=1 or t1=3
有关语句组合(拼接)的注意事项参考如下:
--动态sql语句基本语法
1 :普通SQL语句可以用Exec执行 eg: Select * from tableName
Exec('select * from tableName')
Exec sp_executesql N'select * from tableName' -- 请注意字符串前一定要加N 2:字段名,表名,数据库名之类作为变量时,必须用动态SQL eg:
declare @fname varchar(20)
set @fname = 'FiledName'
Select @fname from tableName -- 错误,不会提示错误,但结果为固定值FiledName,并非所要。
Exec('select ' + @fname + ' from tableName') -- 请注意 加号前后的 单引号的边上加空格 当然将字符串改成变量的形式也可
declare @fname varchar(20)
set @fname = 'FiledName' --设置字段名 declare @s varchar(1000)
set @s = 'select ' + @fname + ' from tableName'
Exec(@s) -- 成功
exec sp_executesql @s -- 此句会报错 declare @s Nvarchar(1000) -- 注意此处改为nvarchar(1000)
set @s = 'select ' + @fname + ' from tableName'
Exec(@s) -- 成功
exec sp_executesql @s -- 此句正确 3. 输出参数
declare @num int,
@sqls nvarchar(4000)
set @sqls='select count(*) from tableName'
exec(@sqls)
--如何将exec执行结果放入变量中? declare @num int,
@sqls nvarchar(4000)
set @sqls='select @a=count(*) from tableName '
exec sp_executesql @sqls,N'@a int output',@num output
select @num