declare @FName2 varchar(20) = 'Ken',
        @PeronType varchar(10) = 'GC',
        @sql nvarchar(1000);
--  不推荐这样使用

exec('select * from Person.Person where FirstName =''' + @FName2 + ''' and PersonType= ''' + @PeronType + '''')
-- sp_executesql 不能接收含有变量拼接的sql字符串。下面的sql执行会报错
-- exec sp_executesql 'select * from Person.Person where FirstName =''' + @FName2 + ''' and PersonType= ''' + @PeronType + ''''
-- 不推荐这样使用：无法防止SQL注入,无法重用执行计划，拼接麻烦且容易出错（字符串类型的需要单引号括起来）
set @sql =  'select * from Person.Person where FirstName =''' + @FName2 + ''' and PersonType= ''' + @PeronType + ''''
exec sp_executesql @sql

declare @FName2 varchar(20) = 'Ken',
	@PeronType varchar(10) = 'GC',
	@sql nvarchar(1000);

-- 推荐先使用变量存放拼接的sql，再使用exec执行sql
set @sql =  'select * from Person.Person where FirstName =''' + @FName2 + ''' and PersonType= ''' + @PeronType + ''''
exec(@sql)

-- 推荐这样使用(可以防止SQL注入，可以重用执行计划）
-- 此处输入参数要加上N,不然会报错：过程需要类型为 'ntext/nchar/nvarchar' 的参数 '@params
set @sql = 'select * from Person.Person where FirstName =@FName and PersonType=@PersonType'
exec sp_executesql @sql, N'@FName varchar(20), @PersonType varchar(10)', @FName2, @PeronType

3. 带有输入参数时的使用

declare @sql nvarchar(1000),
 @cnt int = -1;


-- 使用 exec
-- exec sql内无法访问sql之外定义的变量，直接使用下面的会报错： 必须声明变量 "@cnt"。外部也无法访问到 exec sql里定义的变量
--无法直接将值传出，只能通过select 变量/insert into exec等方式看到值
--exec('select @cnt=count(1) from Person.Person; select @cnt')
exec('declare @cnt int; select @cnt=count(1) from Person.Person')
print @cnt  -- -1, 无法访问 exec 里取到的  @cnt 的值




set @sql = 'select @cnt=count(1) from Person.Person'
exec sp_executesql @sql, N'@cnt int output', @cnt output --此处必须加上ouput，不然无法取到值
print @cnt

4. 带有输入输出参数时的使用

declare @sql nvarchar(1000),
	@cnt int = -1,
	@FName varchar(20) = 'Ken';


exec('declare @cnt int; select @cnt=count(1) from Person.Person where FirstName = ''' + @FName + ''';  select @cnt')
print @cnt  -- -1

set @sql = 'select @cnt=count(1) from Person.Person where FirstName = @FName'
exec sp_executesql @sql, N'@cnt int output, @FName varchar(20)', @cnt output, @FName --此处必须加上ouput，不然无法取到值
print @cnt

5. insert into exec/exec sp_executesql 的使用

declare @tmp table (
	BusinessEntityID int,
	FirstName varchar(50),
	LastName varchar(50)
)

insert into @tmp
exec sp_executesql N'select top 10 BusinessEntityID, FirstName, LastName from Person.Person'

insert into @tmp
exec(N'select top 10 BusinessEntityID, FirstName, LastName from Person.Person')

select * from @tmp

declare @FName2 varchar(20) = 'Ken',
	@PeronType varchar(10) = 'GC',
	@sql nvarchar(1000);

exec sp_executesql 'select * from Person.Person where FirstName =''' + @FName2 + ''' and PersonType= ''' + @PeronType + ''''

    这种情况下，需要先将sql拼凑后的结果放入一个变量中，然后使用 exec sp_executesql 执行；或者使用入参的方式来实现。推荐使用下面的方式

declare @FName2 varchar(20) = 'Ken',
	@PeronType varchar(10) = 'GC',
	@sql nvarchar(1000);
set @sql = 'select * from Person.Person where FirstName = @FName2 and PersonType = @PeronType'
exec sp_executesql @sql, N'@FName varchar(20), @PersonType varchar(10)', @FName2, @PeronType

DBCC FREEPROCCACHE  -- 清空执行计划缓存DECLARE @Sql NVARCHAR(MAX),@ID INT; SET @ID = 15; -- 15使用之后，换成10， 12等再次执行SET @sql = 'SELECT * FROM Person.Person WHERE BusinessEntityID = '+CAST(@ID AS VARCHAR(10))+' ORDER BY BusinessEntityID DESC'EXEC(@sql); SELECT cacheobjtype,objtype,usecounts,sql FROM sys.syscacheobjects WHERE sql NOT LIKE '%cach%' AND sql NOT LIKE '%sys.%'

    使用exec 执行三次后，查询到的执行计划缓存如下

DBCC FREEPROCCACHE

DECLARE @Sql NVARCHAR(MAX),@ID INT; 
SET @ID = 17; 
SET @sql = 'SELECT * FROM Person.Person WHERE BusinessEntityID = @ID ORDER BY BusinessEntityID DESC'
exec sp_executesql @sql, N'@ID int', @ID

SELECT cacheobjtype,objtype,usecounts,sql FROM sys.syscacheobjects WHERE sql NOT LIKE '%cach%' AND sql NOT LIKE '%sys.%'

    同样执行三次之后，查询到的执行计划缓存如下

-- 下面的SQL注入
DECLARE @Sql NVARCHAR(MAX),@FName varchar(20); 
SET @FName = '''ken'' or 1=1'; 
SET @sql = 'SELECT * FROM Person.Person WHERE FirstName = ' + @FName + ' ORDER BY BusinessEntityID DESC'
exec sp_executesql @sql

--下面的可以防止SQL注入
DECLARE @Sql NVARCHAR(MAX),@FName varchar(20); 
SET @FName = '''ken'' or 1=1'; 
SET @sql = 'SELECT * FROM Person.Person WHERE FirstName = @FName ORDER BY BusinessEntityID DESC'
exec sp_executesql @sql, N'@FName varchar(20)', @FName