MSSQL 临时表和公用表使用案例

Posted 2020-09-19 代码艺术

1、临时表：

1.1）实例1

if(OBJECT_ID(‘tempdb..#a‘) IS NOT NULL) drop table #a;
if(OBJECT_ID(‘tempdb..#b‘) IS NOT NULL) drop table #b;
SELECT name into #a from syscolumns a with(nolock) where id=OBJECT_ID(‘NewsLetterSystem_Subscriber‘);
SELECT name into #b from syscolumns b  where id=OBJECT_ID(‘tmpContact_130828005535769_5243_f0b7‘);
select * from #a,#b
where #a.name=#b.name;

1.2） 实例2

if(OBJECT_ID(‘tempdb..#a‘) IS NOT NULL) drop table #a;
select * into #a from Categories;
select * from #a;

 

2、公用表：

2.1）实例1

with
cr as
(
   select CountryRegionCode from person.CountryRegion where Name like ‘C%‘
)

select * from person.StateProvince where CountryRegionCode in (select * from cr)

--其中cr是一个公用表表达式，该表达式在使用上与表变量类似

2.2） CTE后面必须直接跟使用CTE的SQL语句（如select、insert、update等），否则，CTE将失效。如下面的SQL语句将无法正常使用CTE：

with
cr as
(
   select CountryRegionCode from person.CountryRegion where Name like ‘C%‘
)
select * from person.CountryRegion -- 应将这条SQL语句去掉
-- 使用CTE的SQL语句应紧跟在相关的CTE后面 --
select * from person.StateProvince where CountryRegionCode in (select * from cr)

2.3）CTE后面也可以跟其他的CTE，但只能使用一个with，多个CTE中间用逗号（,）分隔，如下面的SQL语句所示：

with
cte1 as
(
   select * from table1 where name like ‘abc%‘
),
cte2 as
(
   select * from table2 where id > 20
),
cte3 as
(
   select * from table3 where price < 100
)
select a.* from cte1 a, cte2 b, cte3 c where a.id = b.id and a.id = c.id

2.4）实例4

with ta as (
 SELECT name  from syscolumns a with(nolock) where id=OBJECT_ID(‘NewsLetterSystem_Subscriber‘)
),
tb as
(
SELECT name from syscolumns b  where id=OBJECT_ID(‘tmpContact_130828005535769_5243_f0b7‘)
)
select * from ta,tb where ta.name=tb.name