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count(1), count(*), count(column)区别 count(1)和count(*)是相同的, 但count(*)代表的语义更明确 COUNT(<expression>) 统计非空值个数 使用IN时是
导出数据 mysqldump -u username -p database_name > data-dump.sql reference 4 Ways to Insert Multiple Rows in Oracle
在线执行环境,缺点是需要注册 Oracle live SQL http://sqlfiddle.com/ 创建用户 alter session set "_ORACLE_SCRIPT"=true; CREATE USER TOM IDENTIFIED BY a12345678; GRANT CONNECT, RESOURCE, DBA TO TOM; GRANT select on tom.contacts TO TOM; REVOKE DBA FROM TOM; REVOKE select on tom.contacts FROM TOM; DROP USER TOM; -- 同时删除用户下的所有对象
查找lock select * from master.dbo.sysprocesses where DB_NAME(dbid)=’test’ and spid<>@@SPID; exec sp_lock exec sp_who2 SPID; select request_session_id, resource_type, resource_description, request_mode, request_status, request_owner_type from sys.dm_tran_locks; kill SPID; 查看表结构 SELECT COLUMN_NAME, DATA_TYPE, CHARACTER_MAXIMUM_LENGTH FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'yourTableName'; 日期 -- 当前时
sqlserver 修改主键约束 sp_help book if exists (select 1 from sysobjects where name = 'PK__book__AFEBF550AD55A29F') begin print 'pk exists' alter table book drop constraint PK__book__AFEBF550AD55A29F end alter table book add constraint PK__book primary key clustered ( book_name asc, id asc ) reference SQL Server 创建表 添加主键 添加列常用SQL语句
sqlserver 事务简单使用 今天第一次在工作中用到事务,在找一个下数量被条件卡住的错误时,是先更新一个表中的数据,在检查数量有没有小于0的,有就要报错。追
sqlserver row_number() 函數的用法 select * from fruit_month_price; select * , row_number() over (partition by name order by year, month) as sn from fruit_month_price order by name,year,month 上面代碼中意為以字段name分組,每組內部以字段year、month(默認升序)