Sqlserver中一直在用又经常被忽略的知识点一
已经有快2个月没有更新博客了，实在是因为最近发生了太多的事情，辞了工作，在湘雅医院待了一个多月，然后又新换了工作......
在平时的工作中，Sqlserver中许多知识点是经常用到的，但是有时候我们往往忽略了它们，在过去的一年里，一直使用的是Mysql，现在又开始接触Sqlserver了，所以就把一些常用又容易忽视的Sqlserver知识点总结一点，以便备忘之用。
所有的操作都将基于Northwind数据库来进行操作。
注意：当采用附加Northwind数据库的方式进行数据库迁移的时候，可能会出现错误：“Access is denied”。解决方案： right-click the SQL Server Management Studio icon and select Run as administrator。
数据在线Mock地址：https://www.mockaroo.com/
SET NOCOUNT ON 介绍
在存储过程中，经常用到SET NOCOUNT ON；
作用：阻止在结果集中返回显示受T-SQL语句或则usp影响的行计数信息。
当SET NOCOUNT ON 时候，不返回计数，当SET NOCOUNT OFF时候，返回计数。
当SET NOCOUNT ON 时候，会更新@@RowCount，但是不向客户端发送存储过程每个语句的DONE_IN_proc消息。
如果存储过程中包含一些并不返回实际数据的语句，使用SET NOCOUNT ON时，网络通信流量便会大量减少，可以显著提高应用程序性能。
SET NOCOUNT 指定的设置只在执行或运行时候生效，分析时候不生效。
示例：
USE Northwind
GO
SET NOCOUNT OFF;
SELECT TOP 5 OrderDate FROM Orders
GO
执行结果如下：
USE Northwind
GO
SET NOCOUNT ON;
SELECT TOP 5 OrderDate FROM Orders
GO
执行结果如下：
Go 介绍
如果只是执行一条语句，有没有GO都一样。
如果多条语句之间用GO分隔开就不一样了。
每个被GO分隔的语句都是一个单独的事务，一个语句执行失败不会影响其它语句执行。
GO 不是 Transact-SQL 语句；而是可为 SQL Server 查询分析器识别的命令。
如果你的SQL过长的时候，就要写GO，或者有一些语句，它只能是第一句操作的，在之前你也得写 GO ，GO的意思是分批处理语句，有加这个 GO ，就执行GO 行的代码，执行后再执行接下来的代码。
像以下这种情况下就要用到GO ，以达到分批处理数据的目的，否则将会报错。
IF EXISTS(SELECT 1 FROM sys.views WHERE name='View_OrderInfo')
DROP VIEW View_OrderInfo
create view View_OrderInfo
as
select c.ContactName,c.CompanyName,o.OrderDate,o.ShipName,o.OrderID,o.Freight from [Orders] o inner join Customers c on o.CustomerID=c.CustomerID
会报错
必须是：
IF EXISTS(SELECT 1 FROM sys.views WHERE name='View_OrderInfo')
DROP VIEW View_OrderInfo
GO
create view View_OrderInfo
as
select c.ContactName,c.CompanyName,o.OrderDate,o.ShipName,o.OrderID,o.Freight from [Orders] o inner join Customers c on o.CustomerID=c.CustomerID
select count(*) count(1) count(2) count('a') 之间的区别
count(*)：找表中最短的列进行统计行数
count(1) count(2) count('a')：对常数列进行统计行数。它们的执行方式是一样的，没有任何区别。
很显然采用count(1) count(2) count('a')的方式，效率会更高，因为count(*)会先去算出最短的列，然后再去统计。虽然现在的Sqlserver查询分析器自动会帮我们做一些优化，但是我们必须知道它们的实现原理。
WITH (NOLOCK)
缺点:
1.会产生脏读
2.只适用于select查询语句
优点:
1.有些文章说，加了WITH (NOLOCK)的SQL查询效率可以增加33%。
2.可以用于inner join 或者left join等语句
脏读: 一个用户对一个资源做了修改，此时另外一个用户正好读取了这条被修改的记录，然后，第一个用户放弃修改，数据回到修改之前，这两个不同的结果就是脏读。
详细内容:
要提升SQL的查询效能，一般来说大家首先会考虑建立索引(index)。其实除了index的建立之外，当我们在下SQL Command时，在语法中加一段WITH (NOLOCK)可以改善在线大量查询的环境中数据集被LOCK的现象藉此改善查询的效能。
不过有一点千万要注意的就是，WITH (NOLOCK)的SQL SELECT有可能会造成Dirty Read(脏读)。
例如：
SELECT o.OrderID,o.OrderDate,o.Freight,d.Quantity,d.UnitPrice
FROM [dbo].[Orders] o WITH (NOLOCK)
JOIN [dbo].[Order Details] d WITH (NOLOCK)
ON o.OrderID=d.OrderID
DELETE、INSERT、UPDATE这些需要transaction的指令就不能使用WITH (NOLOCK)。
加了WITH (NOLOCK)即告诉SQL Server，我们的这段SELECT指令无需去考虑目前table的transaction lock状态，因此效能上会有明显的提升，而且数据库系统的Lock现象会有明显的减少(包含Dead Lock)。
当使用NoLock时，它允许阅读那些已经修改但是还没有交易完成的数据。因此如果有需要考虑transaction事务数据的实时完整性时，使用WITH (NOLOCK)就要好好考虑一下。
如果不需考虑transaction，WITH (NOLOCK)或许是个好用的参考。
Sqlserver高效分页
在SQLserver2012之前，分页我们一般是使用ROW_NUMBER()。以获取第11条到第50条数据为例：
ROW_NUMBER()的实现方式：
select * from (
select *, ROW_NUMBER() OVER(Order by a.OrderID DESC ) AS RowNumber from Orders as a
) as b
where RowNumber BETWEEN 11 and 50
SQLserver2012中OFFSET & FETCH实现方式：
SELECT o.* FROM dbo.Orders o
ORDER BY o.OrderID DESC OFFSET 10 ROWS FETCH NEXT 40 ROWS ONLY
- ORDER BY 是使用 OFFSET 和 FETCH 子句所必需的。
- OFFSET 子句必须与 FETCH 一起使用。永远不能使用 ORDER BY … FETCH。
- TOP 不能在同一个查询表达式中与 OFFSET 和 FETCH 一起使用。
- OFFSET/FETCH 行计数表达式可以是将返回整数值的任何算术、常量或参数表达式。该行计数表达式不支持标量子查询
ALTER PROCEDURE getLightningSendOverTimeOrder --闪电送到期存储过程
(@OverTimeMinutes INT,--超时时间阈值
@GetLasterDay int --取最近多少天的订单
)
As
DECLARE @sql NVARCHAR(MAX);
BEGIN
set nocount on;
set @Sql=
N'WITH OrderInfo
--查询近一天的，处理超时的闪电送订单
AS ( SELECT ID ,
CommunityId ,
SubOrderNumber
FROM dbo.[Order] WITH ( NOLOCK )
WHERE DATEDIFF(day, CreatedOn, GETDATE()) <= @GetLasterDay
AND DATEDIFF(mi, CreatedOn, ModifiedOn) > @OverTimeMinutes
AND LightningSend = 1
AND IsDeleted = 0
--待付款(商品订单),待确认(商品订单),待发货(商品订单),待收货(商品订单)
AND OrderStatusId IN (
''C2EE784F-F29B-4E18-8D73-761264339005'',
''FA1A31DF-3855-41BB-9F5C-A09F3AB4C408'',
''ACF190B2-0CA2-43A0-8E6B-70DF8521F4C5'',
''15F06407-C82C-4CA8-984E-37FB3BD9963C'' )
),
SmsOrder
--没有发送过信息的订单
AS ( SELECT o.ID ,
o.CommunityId ,
o.SubOrderNumber
FROM OrderInfo o WITH ( NOLOCK )
where not EXISTS(SELECT 1 FROM [dbo].[Sms_LightningSendOrderOverTime] lso
WITH ( NOLOCK ) WHERE o.SubOrderNumber = lso.SubOrderNumber)
),
SmsOrderInfo
AS ( SELECT
so.CommunityId ,
so.SubOrderNumber ,
p.PublisherId ,
c.ConvenienceStoreID ,
oi.ProductId ,
p.CategoryId ,
p.ProcessType
FROM SmsOrder AS so WITH ( NOLOCK )
INNER JOIN Community c WITH ( NOLOCK ) ON so.CommunityId = c.ID
INNER JOIN dbo.OrderItem oi WITH ( NOLOCK ) ON so.ID = oi.OrderId
INNER JOIN dbo.Product p WITH ( NOLOCK ) ON oi.ProductId = p.Id
AND p.LightningSend = 1
AND p.ProcessType != 1 -- 便利店
),
MerchantSmsOrderInfo
AS ( SELECT
so.CommunityId ,
so.SubOrderNumber ,
p.PublisherId ,
c.ConvenienceStoreID ,
oi.ProductId ,
p.CategoryId ,
p.ProcessType
FROM SmsOrder AS so WITH ( NOLOCK )
INNER JOIN Community c WITH ( NOLOCK ) ON so.CommunityId = c.ID
INNER JOIN dbo.OrderItem oi WITH ( NOLOCK ) ON so.ID = oi.OrderId
INNER JOIN dbo.Product p WITH ( NOLOCK ) ON oi.ProductId = p.Id
AND p.LightningSend = 1
AND p.ProcessType = 1 -- 商家
),
ResultInfo
AS (
SELECT usr.Id AS UserId ,
soi.SubOrderNumber ,
usr.PhoneNumber
FROM SmsOrderInfo AS soi
INNER JOIN dbo.[User] AS usr WITH ( NOLOCK ) ON soi.ConvenienceStoreID = usr.OrgId
INNER JOIN dbo.Organization org WITH ( NOLOCK ) ON usr.OrgId = org.Id
AND org.Levels = 2 --便利店
INNER JOIN OrderDistributaryCategoryRelation AS odcr
WITH ( NOLOCK ) ON usr.Id = odcr.MerchantUserId
AND odcr.CategoryType = 1
AND odcr.SellerId = soi.ConvenienceStoreID
AND odcr.CategoryId = soi.CategoryId
INNER JOIN OrderDistributary AS odb WITH ( NOLOCK ) ON usr.Id = odb.MerchantUserId
AND odb.SellerId = soi.ConvenienceStoreID
INNER JOIN OrderDistributaryRelation AS odbr WITH ( NOLOCK ) ON usr.Id = odbr.MerchantUserId
AND odbr.MerchantId = soi.ConvenienceStoreID
UNION ALL
SELECT u.Id AS UserId ,
soi.SubOrderNumber ,
u.PhoneNumber
FROM dbo.[User] u WITH ( NOLOCK )
INNER JOIN OrderDistributary odb WITH ( NOLOCK ) ON u.Id = odb.MerchantUserId
AND odb.IsDefault = 1
INNER JOIN SmsOrderInfo soi WITH ( NOLOCK ) ON odb.SellerId = soi.ConvenienceStoreID
------------------------------商家-----------------------------
UNION ALL
SELECT usr.Id AS UserId ,
soi.SubOrderNumber ,
usr.PhoneNumber
FROM MerchantSmsOrderInfo AS soi
INNER JOIN dbo.[User] AS usr WITH ( NOLOCK ) ON soi.ConvenienceStoreID = usr.OrgId
INNER JOIN dbo.Organization org WITH ( NOLOCK ) ON usr.OrgId = org.Id
AND org.Levels = 1 --商家
INNER JOIN OrderDistributaryCategoryRelation AS odcr
WITH ( NOLOCK ) ON usr.Id = odcr.MerchantUserId
AND odcr.CategoryType = 1
AND odcr.CategoryId = soi.CategoryId
INNER JOIN OrderDistributary AS odb WITH ( NOLOCK ) ON usr.Id = odb.MerchantUserId
AND odb.SellerId = soi.PublisherId
INNER JOIN OrderDistributaryRelation AS odbr WITH ( NOLOCK ) ON odcr.MerchantUserId = odbr.MerchantUserId
AND odbr.MerchantId = soi.ConvenienceStoreID
UNION ALL
SELECT u.Id AS UserId ,
soi.SubOrderNumber ,
u.PhoneNumber
FROM MerchantSmsOrderInfo soi WITH ( NOLOCK )
INNER JOIN OrderDistributary odb WITH ( NOLOCK ) ON odb.SellerId = soi.PublisherId
AND odb.IsDefault = 1
AND odb.IsDeleted = 0
INNER JOIN dbo.[User] u WITH ( NOLOCK ) ON u.Id = odb.MerchantUserId
)
SELECT r.SubOrderNumber ,
r.UserId,
r.PhoneNumber
FROM ResultInfo r '
exec sp_executesql @Sql,N'@OverTimeMinutes int,@GetLasterDay int',@OverTimeMinutes,@GetLasterDay;
SET NOCOUNT OFF;
END
自己写的一个存储过程例子
--------------------------------------创建闪电送存储过程-----------------------------------
IF EXISTS(Select Name From Sysobjects Where Name='getLightningSendOverTimeOrder' And Xtype='P')
DROP PROCEDURE [dbo].getLightningSendOverTimeOrder
GO
CREATE PROCEDURE getLightningSendOverTimeOrder --闪电送到期存储过程
(@OverTimeMinutes INT,--超时时间阈值
@GetLasterDay int --取最近多少天的订单
)
As
DECLARE @sql NVARCHAR(MAX);
BEGIN
set nocount on;
set @Sql=
N'WITH OrderInfo
--查询近一天的，处理超时的闪电送订单
AS ( SELECT ID ,
CommunityId ,
SubOrderNumber
FROM dbo.[Order] WITH ( NOLOCK )
WHERE DATEDIFF(day, CreatedOn, GETDATE()) <= @GetLasterDay
AND DATEDIFF(mi, CreatedOn, ModifiedOn) > @OverTimeMinutes
AND LightningSend = 1
AND IsDeleted = 0
--待付款(商品订单),待确认(商品订单),待发货(商品订单),待收货(商品订单)
AND OrderStatusId IN (
''C2EE784F-F29B-4E18-8D73-761264339005'',
''FA1A31DF-3855-41BB-9F5C-A09F3AB4C408'',
''ACF190B2-0CA2-43A0-8E6B-70DF8521F4C5'',
''15F06407-C82C-4CA8-984E-37FB3BD9963C'' )
UNION ALL
--状态一直是待支付状态的
SELECT ID ,
CommunityId ,
SubOrderNumber
FROM dbo.[Order] WITH ( NOLOCK )
WHERE DATEDIFF(day, CreatedOn, GETDATE()) <=@GetLasterDay
AND LightningSend = 1
AND IsDeleted = 0
AND (OrderStatusId =''ACF190B2-0CA2-43A0-8E6B-70DF8521F4C5'' AND DATEDIFF(mi, CreatedOn, GETDATE()) >@OverTimeMinutes)
),
SmsOrder
--需要发送过信息的订单
AS ( SELECT o.ID ,
o.CommunityId ,
o.SubOrderNumber
FROM OrderInfo o WITH ( NOLOCK )
where not EXISTS(SELECT 1 FROM [dbo].[Sms_LightningSendOrderOverTime] lso
WITH ( NOLOCK ) WHERE o.SubOrderNumber = lso.SubOrderNumber)
),
SmsOrderInfo
AS ( SELECT
so.CommunityId ,
so.SubOrderNumber ,
p.PublisherId ,
c.ConvenienceStoreID ,
oi.ProductId ,
p.CategoryId ,
p.ProcessType
FROM SmsOrder AS so WITH ( NOLOCK )
INNER JOIN Community c WITH ( NOLOCK ) ON so.CommunityId = c.ID
INNER JOIN dbo.OrderItem oi WITH ( NOLOCK ) ON so.ID = oi.OrderId
INNER JOIN dbo.Product p WITH ( NOLOCK ) ON oi.ProductId = p.Id
AND p.LightningSend = 1
AND p.ProcessType != 1 -- 便利店
),
MerchantSmsOrderInfo
AS ( SELECT
so.CommunityId ,
so.SubOrderNumber ,
p.PublisherId ,
c.ConvenienceStoreID ,
oi.ProductId ,
p.CategoryId ,
p.ProcessType
FROM SmsOrder AS so WITH ( NOLOCK )
INNER JOIN Community c WITH ( NOLOCK ) ON so.CommunityId = c.ID
INNER JOIN dbo.OrderItem oi WITH ( NOLOCK ) ON so.ID = oi.OrderId
INNER JOIN dbo.Product p WITH ( NOLOCK ) ON oi.ProductId = p.Id
AND p.LightningSend = 1
AND p.ProcessType = 1 -- 商家
),
ResultInfo
AS (
SELECT usr.Id AS UserId ,
soi.SubOrderNumber ,
usr.PhoneNumber
FROM SmsOrderInfo AS soi
INNER JOIN dbo.[User] AS usr WITH ( NOLOCK ) ON soi.ConvenienceStoreID = usr.OrgId
INNER JOIN dbo.Organization org WITH ( NOLOCK ) ON usr.OrgId = org.Id
AND org.Levels = 2 --便利店
INNER JOIN OrderDistributaryCategoryRelation AS odcr
WITH ( NOLOCK ) ON usr.Id = odcr.MerchantUserId
AND odcr.CategoryType = 1
AND odcr.SellerId = soi.ConvenienceStoreID
AND odcr.CategoryId = soi.CategoryId
INNER JOIN OrderDistributary AS odb WITH ( NOLOCK ) ON usr.Id = odb.MerchantUserId
AND odb.SellerId = soi.ConvenienceStoreID
INNER JOIN OrderDistributaryRelation AS odbr WITH ( NOLOCK ) ON usr.Id = odbr.MerchantUserId
AND odbr.MerchantId = soi.ConvenienceStoreID
UNION ALL
SELECT u.Id AS UserId ,
soi.SubOrderNumber ,
u.PhoneNumber
FROM dbo.[User] u WITH ( NOLOCK )
INNER JOIN OrderDistributary odb WITH ( NOLOCK ) ON u.Id = odb.MerchantUserId
AND odb.IsDefault = 1
INNER JOIN SmsOrderInfo soi WITH ( NOLOCK ) ON odb.SellerId = soi.ConvenienceStoreID
------------------------------商家-----------------------------
UNION ALL
SELECT usr.Id AS UserId ,
soi.SubOrderNumber ,
usr.PhoneNumber
FROM MerchantSmsOrderInfo AS soi
INNER JOIN dbo.[User] AS usr WITH ( NOLOCK ) ON soi.ConvenienceStoreID = usr.OrgId
INNER JOIN dbo.Organization org WITH ( NOLOCK ) ON usr.OrgId = org.Id
AND org.Levels = 1 --商家
INNER JOIN OrderDistributaryCategoryRelation AS odcr
WITH ( NOLOCK ) ON usr.Id = odcr.MerchantUserId
AND odcr.CategoryType = 1
AND odcr.CategoryId = soi.CategoryId
INNER JOIN OrderDistributary AS odb WITH ( NOLOCK ) ON usr.Id = odb.MerchantUserId
AND odb.SellerId = soi.PublisherId
INNER JOIN OrderDistributaryRelation AS odbr WITH ( NOLOCK ) ON odcr.MerchantUserId = odbr.MerchantUserId
AND odbr.MerchantId = soi.ConvenienceStoreID
UNION ALL
SELECT u.Id AS UserId ,
soi.SubOrderNumber ,
u.PhoneNumber
FROM MerchantSmsOrderInfo soi WITH ( NOLOCK )
INNER JOIN OrderDistributary odb WITH ( NOLOCK ) ON odb.SellerId = soi.PublisherId
AND odb.IsDefault = 1
AND odb.IsDeleted = 0
INNER JOIN dbo.[User] u WITH ( NOLOCK ) ON u.Id = odb.MerchantUserId
)
SELECT r.SubOrderNumber ,
r.UserId,
r.PhoneNumber
FROM ResultInfo r '
exec sp_executesql @Sql,N'@OverTimeMinutes int,@GetLasterDay int',@OverTimeMinutes,@GetLasterDay;
SET NOCOUNT OFF;
END GO
demo2:分页存储过程
------------------------------------------创建我的优惠券存储过程 created by zouqj-2017-3-1-----------------------------------
IF EXISTS(Select Name From Sysobjects Where Name='usp_GetMyCouponsList' And Xtype='P')
DROP PROCEDURE usp_GetMyCouponsList
GO
CREATE PROC usp_GetMyCouponsList
(
@PageIndex int, --页码
@PageSize int, --
@hostName nvarchar(100),--服务器地址
@MemberID UNIQUEIDENTIFIER, --会员ID
@IsGetTotalInfo BIT, --是否得到统计信息，1为得到统计信息，0为不得到统计信息，返回记录集
@HasStatus BIT, -- 是否有状态
@CouponsStatus INT --优惠券状态
)
AS
----------------------------------------定义参数--------------------------------------
declare @strSql NVARCHAR(max);
DECLARE @IsUseCount INT
DECLARE @ExpiredCount INT
DECLARE @NoUseCount INT
DECLARE @where NVARCHAR(100);
set nocount on;
----------------------------------------SQL开始--------------------------------------
IF @HasStatus=1
BEGIN
SET @where='m.[State]=@CouponsStatus';
END
ELSE
BEGIN
SET @where='1=1'
END
IF @IsGetTotalInfo=0
BEGIN
SET @strSql=N'SELECT DISTINCT t.* FROM (SELECT m.[State] AS [STATUS],
m.CouponCode AS CouponsCode,
m.CampaignID AS CampaignID,
c.Code as CampaignCode,
c.Name AS CampaignName,
b.ValidityStartTime AS CampaignStartTime,
b.ValidityEndTime AS CampaignEndTime,
c.Price as CouponsAmount,
(CASE WHEN c.IsLimited =1 THEN 1 ELSE 2 END ) as IsLimited,
c.FullAmount as MinAmount,
e.[Type] AS CouponsType,
(CASE WHEN b.IconUrl IS NULL THEN N'''' WHEN b.IconUrl=N'''' THEN N'''' ELSE @hostName+b.IconUrl END) AS IconUrl FROM Loy_MemberCoupon m WITH ( NOLOCK ) INNER JOIN
[dbo].[MK_Campaign] AS a WITH ( NOLOCK ) ON m.CampaignID=a.ID AND m.MemberID=@MemberID AND '+@where+'
LEFT OUTER JOIN [dbo].[MK_CouponConfig] AS b WITH ( NOLOCK ) ON a.[ID] = b.[CampaignID]
LEFT OUTER JOIN [dbo].[MK_Coupon] AS c WITH ( NOLOCK ) ON b.[CouponID] = c.[ID]
LEFT OUTER JOIN [dbo].[MK_CouponRestriction] AS d WITH ( NOLOCK ) ON c.[ID] = d.[CompainID]
LEFT OUTER JOIN [dbo].[MK_CouponRestrictCategory] AS e WITH ( NOLOCK ) ON d.[ID] = e.[CouponRestrictionID]
) t
ORDER BY t.CampaignEndTime
offset (@PageIndex-1)*@PageSize ROWS FETCH NEXT @PageIndex*@PageSize ROWS ONLY'
exec sp_executesql @strSql,N'@PageIndex int,@PageSize int,@hostName nvarchar(100),@MemberID UNIQUEIDENTIFIER,@where NVARCHAR(100),@CouponsStatus int',@PageIndex=@PageIndex,@PageSize=@PageSize,@hostName=@hostName,@MemberID=@MemberID,@where=@where,@CouponsStatus=@CouponsStatus
END
ELSE
BEGIN
-------------------------------------------------------------
SELECT @IsUseCount=COUNT(1) FROM (SELECT DISTINCT m.CouponCode
FROM Loy_MemberCoupon m WITH ( NOLOCK ) WHERE m.MemberID=@MemberID AND m.[State]=2
) t
SELECT @ExpiredCount=COUNT(1) FROM (SELECT DISTINCT m.CouponCode
FROM Loy_MemberCoupon m WITH ( NOLOCK ) WHERE m.MemberID=@MemberID AND m.[State]=3
) t
SELECT @NoUseCount=COUNT(1) FROM (SELECT DISTINCT m.CouponCode
FROM Loy_MemberCoupon m WITH ( NOLOCK ) WHERE m.MemberID=@MemberID AND m.[State]=1
) t
SELECT @IsUseCount AS IsUseCount,@ExpiredCount AS ExpiredCount,@NoUseCount AS NoUseCount
END
----------------------------------------SQL结束--------------------------------------
set nocount off;
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