1 SELECT COUNT(*)與SELECT COUNT(column_or_expression)的區別

SELECT COUNT(*):包括 NULL值;

SELECT COUNT(column_or_expression):不包括NULL值;

如果這兩個都可以滿足一需求時，并且在column上無Index時，建義用COUNT(*), 因為COUNT(*)能用到表上任意一個Index.

2, SQL JOINS（轉）

感覺這篇文章，對初學SQL的人會有一些幫助原文：Visual Representation of SQL Joins

3, SQL SERVER　通過 FOR XML PATH子句，將多行轉成一列（以逗號隔開）（轉）

原方地址：Exploring Database Schemas on SQL Server

SELECT t.TABLE_SCHEMA,t.TABLE_NAME,STUFF(( SELECT ',' + COLUMN_NAMEFROM INFORMATION_SCHEMA.COLUMNS AS cWHERE c.TABLE_SCHEMA = t.TABLE_SCHEMAAND c.TABLE_NAME = t.TABLE_NAMEORDER BY c.COLUMN_NAMEFORXML PATH('')), 1, 1, '') AS Columns FROM INFORMATION_SCHEMA.TABLES AS t

備注：Here we look up a list of tables and do a correlated subquery on the COLUMNS view to find out all the columns contained in that table. FOR XML PATH(‘’) causes all the results to be concatenated into a single value. The STUFF function simply removes the leading comma that would otherwise appear at the start of the list.

4, 獲取數據庫所有外鍵的SQL

View Code SELECT OBJECT_SCHEMA_NAME(f.parent_object_id) AS TableNameSchema, -- thisOBJECT_NAME(f.parent_object_id) AS TableName,COL_NAME(fc.parent_object_id,fc.parent_column_id) AS ColumnName,OBJECT_SCHEMA_NAME(f.referenced_object_id) AS ReferenceTableNameSchema, -- thisOBJECT_NAME (f.referenced_object_id) AS ReferenceTableName,COL_NAME(fc.referenced_object_id,fc.referenced_column_id) AS ReferenceColumnName,f.name AS ForeignKey FROMsys.foreign_keys AS fINNER JOIN sys.foreign_key_columns AS fc ON f.OBJECT_ID = fc.constraint_object_idINNER JOIN sys.objects AS o ON o.OBJECT_ID = fc.referenced_object_id

5,SQL Server 臨時禁用和啟用所有外鍵約束

--獲得禁用所有外鍵約束的語句 select 'ALTER TABLE [' + b.name + '] NOCHECK CONSTRAINT ' + a.name +';' as 禁用約束 from sysobjects a ,sysobjects b where a.xtype ='f' and a.parent_obj = b.id --獲得啟用所有外鍵約束的語句 select 'ALTER TABLE [' + b.name + '] CHECK CONSTRAINT ' + a.name +';' as 啟用約束 from sysobjects a ,sysobjects b where a.xtype ='f' and a.parent_obj = b.id View Code

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6,SQL在線格式化工具

Instant SQL Formatter

7,SQLSERVER恢復刪除的數據（轉dudu實戰 SQL Server 2008 數據庫誤刪除數據的恢復)

總共三個步驟：

• 備份當前數據庫的事務日志：BACKUP LOG [數據庫名] TO disk= N'備份文件名' WITH NORECOVERY
• 恢復一個誤刪除之前的完全備份：RESTORE DATABASE [數據庫名] FROM DISK = N'完全備份文件名' WITH NORECOVERY,? REPLACE
• 將數據庫恢復至誤刪除之前的時間點：RESTORE LOG [數據庫] FROM? DISK = N'第一步的日志備份文件名' WITH?? STOPAT = N'誤刪除之前的時間點' , RECOVERY

總的來說，在誤刪除數據后，做的第一件是就是備份數據庫操作日志，并記下刪除操作時間；然后恢復完全備份的數據庫（所以在開發時也要養成備份數據庫的習慣）；最后恢復操作日志到刪除操作時間之前。

8, SQL UPDATE語句與INNER JOIN 結合

UPDATE T2SET ID=REPLACE(T.ID,'Start','TKStart') FROM T2INNER JOIN T ON T2.ID=T.ID

9, sql server 查詢表結構（轉自reglong sql server 查詢表結構 ）

--1：獲取當前數據庫中的所有用戶表select Name from sysobjects where xtype='u' and status>=0--2：獲取某一個表的所有字段select name from syscolumns where id=object_id('表名')--3：查看與某一個表相關的視圖、存儲過程、函數select a.* from sysobjects a, syscomments b where a.id = b.id and b.text like '%表名%'--4：查看當前數據庫中所有存儲過程select name as 存儲過程名稱 from sysobjects where xtype='P'--5：查詢用戶創建的所有數據庫select * from master..sysdatabases D where sid not in(select sid from master..syslogins where name='sa')或者select dbid, name AS DB_NAME from master..sysdatabases where sid <> 0x01--6：查詢某一個表的字段和數據類型select column_name,data_type from information_schema.columns where table_name = '表名'
--6.1 EXAMPLE
SELECT TABLE_NAME,column_name,NUMERIC_SCALE,data_type
FROM information_schema.columns
WHERE DATA_TYPE='decimal'
ORDER BY TABLE_NAME

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轉載于:https://www.cnblogs.com/dataadapter/archive/2013/03/27/2969014.html

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