SQL Server automatically parameterized statements

Original: SQL Server in a statement autoparameterization

 

   
   
use master
go

if exists( select * from sys.databases where name = 'test')
drop database test
go

--创建数据库
create database test

if exists( select * from sys.tables where name = 't')
drop table t
go


--1.创建表t
create table t(i int);


--2.添加100000条记录,消耗56秒
declare @i int;
declare @ sql varchar( 1000);

set @i = 1
set @ sql = '';

while @i <= 100000
begin
set @ sql = 'insert into t values(' + cast(@i as varchar) + ')'
begin tran

exec(@ sql)
commit tran

set @i = @i + 1
end


--3.1查询的统计信息
--但发现没有返回记录
select st.text,
SUBSTRING(st.text, (qs.statement_start_offset/ 2)+ 1,
(( CASE qs.statement_end_offset
WHEN -1 THEN DATALENGTH(st.text)
ELSE qs.statement_end_offset
END - qs.statement_start_offset)/ 2) + 1) AS statement_text,
qs.*
from sys.dm_exec_query_stats qs
cross apply sys.dm_exec_sql_text(qs.sql_handle) st
where cast(st.text as varchar) like '%insert into t values%'



--3.2查询的统计信息
--有返回,说明SQL Server在执行动态生成的语句时,已经参数化了
--execution_count字段的值为100000
select st.text,
SUBSTRING(st.text, (qs.statement_start_offset/ 2)+ 1,
(( CASE qs.statement_end_offset
WHEN -1 THEN DATALENGTH(st.text)
ELSE qs.statement_end_offset
END - qs.statement_start_offset)/ 2) + 1) AS statement_text,
qs.*
from sys.dm_exec_query_stats qs
cross apply sys.dm_exec_sql_text(qs.sql_handle) st
where cast(st.text as varchar) like '%insert into%'


--3.3 查看数据库是否强制参数化
--并没有强制参数化,说明上面是系统自动对语句进行参数化了
select name,
is_parameterization_forced --返回0,说明并没有强制参数
from sys.databases
where name = 'test'


--3.4 再次执行后，再次执行3.2后发现，execution_count为100001
insert into t values( 100001)

--3.5 这次在语句中加了空格,execution_count为100002
insert into t values( 100002 )


--3.5 这次在语句中加了架构
--返回2条记录，一条为100002，另一个为1
--虽然2条数据的sql_handle、plan_handle都不相同，但是query_hash、query_plan_hash相同
insert into dbo.t values( 100003 )


--3.6 显示缓存的执行计划
--返回2条数据，一条为100002，一个为1
--缓存对象类型为编译计划，对象类型为Prepared
select *
from sys.dm_exec_cached_plans cp
cross apply sys.dm_exec_sql_text(cp.plan_handle) st
where st.text like '%insert into%'


  
  

 

 To sum up:

1. For some of the more simple statement, SQL Server can automatically parameterize automatically ignores spaces.

 

2. But there is no statement at the same time, such as adding a schema object belongs, the system is no way to parameterize, but it is interesting that query_hash and query_plan_hash are the same, that is the nature of these queries Ming are the same.

   So can these hash values ​​group by, the compiler calculated how many times.