常用SQL

一、基础SQL语句

参考文章

1. 创建数据库
   create database db_name;

2. 删除数据库
   drop database db_name;

3. 数据库备份
   --- 创建 备份数据的 device
   USE master
   exec sp_addumpdevice 'disk', 'testBack', 'd:\mysql7backup\MyNwind_1.dat'
   --- 开始 备份
   BACKUP DATABASE pubs TO testBack

4. 创建新表
   create table tb_name(
   column_name type [not null] primary key [auto_increment],
   column_name2 type2......)
   从旧表选字段建新表
   create table tb_name like old_tb
   或
   create table tb_name as select col1,col2 from old_tb definition only

5. 修改字段数据类型 modify
   alter table tb_name modify col_name new_type [not null];

6. 修改字段名称 change
   alter table tb_name change old_name new_name;

7. 删除字段
   alter table tb_name drop col_name;

8. 创建索引
   create [unique] index index_name on tb_name(column(length));

9. 综合常用语句
   选择：select * from tb_name where 范围
   插入：insert into tb_name(field1,field2) values(v1,v2)
   删除：delete from tb_name where 范围
   更新：update tb_name set field1=v1 where 范围
   查找：select * from tb_name where field1 like ’v1%’ ---切勿左模糊
   排序：select * from tb_name order by field1,field2 [asc]
   总数：select count as totalcount from tb_name
   求和：select sum(field1) as sumvalue from tb_name
   平均：select avg(field1) as average from tb_name
   最大：select max(field1) as maxvalue from tb_name
   最小：select min(field1) as minvalue from tb_name

10. 连接（连表）
    left join 左连接
    select a.a, b.b from a left join b on a.a=b.b;

right join 同理右连接 或 full join

11. group by 分组
    一张表分组 完成后，查询后只能得到组相关的信息。
    组相关的信息：（统计信息） count,sum,max,min,avg 分组的标准)
    select sum(col) from tb_name group by col2;

12. 对数据库进行操作：
    分离数据库： sp_detach_db;附加数据库：sp_attach_db 后接表明，附加需要完整的路径名

&bsp;

二、常见

1. top子句
   SQL server的语法：
   select top num | percent col_name from tb_name;
   --
   例子：从表students中选取前2行的数据；
   select top 2 * from students;
   --
   从表中取前30%的学生姓名：
   select top 30 percent name from students;
   --
   MySQL的语法：
   select col_name from tb_name limit num offset num;
   --
   如：查看3行数据，偏移量5，意思从第5行开始看到第8行：
   select * from students limit 3 offset 5

2. 复制表-不带数据
   select top 0 * into new from old;

3. 拷贝表-带数据
   insert into new(col1,col2,col3) select d,e,f from old;

4. 子查询
   select x,y from a where x in (select d from b);

5. between 范围之间
   select * from tb_name where id between n1 and n2;
   同理not between
   mysql中可用大于> 或者小于< and 连接。

6. in 在里面
   select * from tb_name where id in (v1, v2, v3);
   同理 not in
   注意not in在连表查询时如有null值，则出现无数据bug不好用，可使用not exist

7. 说明：两张关联表，删除主表中已经在副表中没有的信息
   delete from tb1 where not exists ( select * from tb2 where tb1.field1=tb2.field1 )

8. 随机选择
   select newid();

9. 删除重复记录
   delet from tb_name where id not in (select max(id) from tb_name group by (col1, col2...));
   或者
   select distinct * into temp from tb_name
   delete from tb_name
   insert into tb_name select * from temp

10. 列出数据库里所有的表名
    select name from sysobjects where type='U' // U代表用户

11. 列出表里的所有的列名
    select name from syscolumns where id=object_id('TableName')

12. 压缩数据库
    dbcc shrinkdatabase(dbname)

13. 转移数据库给新用户以已存在用户权限
    exec sp_change_users_login 'update_one','newname','oldname'
    go

14. 检查备份集
    RESTORE VERIFYONLY from disk='E:\dvbbs.bak'

15. 修复数据库
    ALTER DATABASE [dvbbs] SET SINGLE_USER
    GO
    DBCC CHECKDB('dvbbs',repair_allow_data_loss) WITH TABLOCK
    GO
    ALTER DATABASE [dvbbs] SET MULTI_USER
    GO

16. 日志清除
    SET NOCOUNT ON
    DECLARE @LogicalFileName sysname,
    @MaxMinutes INT,
    @NewSize INT
    --
    USE tablename -- 要操作的数据库名
    SELECT @LogicalFileName = 'tablename_log', -- 日志文件名
    @MaxMinutes = 10, -- Limit on time allowed to wrap log.
    @NewSize = 1 -- 你想设定的日志文件的大小(M)
    --
    Setup / initialize
    DECLARE @OriginalSize int
    SELECT @OriginalSize = size
    FROM sysfiles
    WHERE name = @LogicalFileName
    SELECT 'Original Size of ' + db_name() + ' LOG is ' +
    CONVERT(VARCHAR(30),@OriginalSize) + ' 8K pages or ' +
    CONVERT(VARCHAR(30),(@OriginalSize8/1024)) + 'MB'
    FROM sysfiles
    WHERE name = @LogicalFileName
    CREATE TABLE DummyTrans
    (DummyColumn char (8000) not null)
    --
    DECLARE @Counter INT,
    @StartTime DATETIME,
    @TruncLog VARCHAR(255)
    SELECT @StartTime = GETDATE(),
    @TruncLog = 'BACKUP LOG ' + db_name() + ' WITH TRUNCATE_ONLY'
    --
    DBCC SHRINKFILE (@LogicalFileName, @NewSize)
    EXEC (@TruncLog)
    -- Wrap the log if necessary.
    WHILE @MaxMinutes > DATEDIFF (mi, @StartTime, GETDATE()) -- time has not expired
    AND @OriginalSize = (SELECT size FROM sysfiles WHERE name = @LogicalFileName)
    AND (@OriginalSize * 8 /1024) > @NewSize
    BEGIN -- Outer loop.
    SELECT @Counter = 0
    WHILE ((@Counter < @OriginalSize / 16) AND (@Counter < 50000))
    BEGIN -- update
    INSERT DummyTrans VALUES ('Fill Log') DELETE DummyTrans
    SELECT @Counter = @Counter + 1
    END
    EXEC (@TruncLog)
    END
    SELECT 'Final Size of ' + db_name() + ' LOG is ' +
    CONVERT(VARCHAR(30),size) + ' 8K pages or ' +
    CONVERT(VARCHAR(30),(size8/1024)) + 'MB'
    FROM sysfiles
    WHERE name = @LogicalFileName
    DROP TABLE DummyTrans
    SET NOCOUNT OFF

17. 说明：更改某个表
    exec sp_changeobjectowner 'tablename','dbo'