在sql里面,那些单引号如何看比较好啊,下面的这个sql存储过程里的单引号看得我头都晕了,有什么比较好的方法理解吗?
BEGIN
EXEC dbo.sp_executesql @statement = N' CREATE PROCEDURE [bookconditionsearch]
(@classfy [varchar](50),
@type [varchar](10),
@content [varchar](50),
@mode [int]
)
AS
begin
declare @sql nvarchar(1000) --生成的sql语句
if @classfy=''所有书刊''
begin
if @mode=1
begin
set @sql=''select * from books where ''+@type+'' like ''''''+@content+''%''''''
exec sp_executesql @sql
end else
begin
set @sql=''select * from books where ''+@type+'' like ''''%''+@content+''%''''''
exec sp_executesql @sql
end
end
else
begin
if @mode=1
begin
set @sql=''select * from books where bookclassfy=''''''+@classfy+'''''' and ''+@type+'' like ''''''+@content+''%''''''
exec sp_executesql @sql
end
else
begin
set @sql=''select * from books where bookclassfy=''''''+@classfy+'''''' and ''+@type+'' like ''''%''+@content+''%''''''
exec sp_executesql @sql
end
end
end
'
END
BEGIN
EXEC dbo.sp_executesql @statement = N' CREATE PROCEDURE [bookconditionsearch]
(@classfy [varchar](50),
@type [varchar](10),
@content [varchar](50),
@mode [int]
)
AS
begin
declare @sql nvarchar(1000) --生成的sql语句
if @classfy=''所有书刊''
begin
if @mode=1
begin
set @sql=''select * from books where ''+@type+'' like ''''''+@content+''%''''''
exec sp_executesql @sql
end else
begin
set @sql=''select * from books where ''+@type+'' like ''''%''+@content+''%''''''
exec sp_executesql @sql
end
end
else
begin
if @mode=1
begin
set @sql=''select * from books where bookclassfy=''''''+@classfy+'''''' and ''+@type+'' like ''''''+@content+''%''''''
exec sp_executesql @sql
end
else
begin
set @sql=''select * from books where bookclassfy=''''''+@classfy+'''''' and ''+@type+'' like ''''%''+@content+''%''''''
exec sp_executesql @sql
end
end
end
'
END
字符串里面的字符常量用“''”,字符串里面代表字符类型的变量用“'''”,
楼主可以 Print @sql,看看真正执行的sql语句到底是什么来理解此春出过程
--print @sql --看看declare @sql varchar(10)
set @sql='''好的'''
print @sql
/*'好的'
*/
注意字符串边界符(默认为('))的问题,为了正确区分字符串边界符和字符串中包含的字符串边界符
SQLMSQL中要求字符串中出现的字符串边界符,一律要用2个字符的边界符来表示
--到查询分析器里执行一下下面的语句就好理解了
select ''''select '''a'''
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
简单的一个例子:select '''string''' 结果为:'string'