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优化SQL查询:如何写出高性能SQL语句优化SQL查询:如何写出高性能SQL语句1、 首先要搞明白什么叫执行计划?8、 一些SQL查询语句应加上nolock在SQL语句中加nolock是提高SQL Server并发性能的重要手段,在oracle中并不需要这样做,因为oracle的结构更为合理,有undo表空间保存“数据前影”,该数据如果在修改中还未commit,那么你读到的是它修改... 阅9 转0 评0 公众公开 15-06-30 15:04 |
mysql 海量数据统计处理 模拟物化视图[java] view plaincopy一 物化视图 物化视图,它是用于预先计算并保存表连接或聚集等耗时较多的操作的结果,这样,在执行查询时,就可以避免进行这些耗时的操作,而从快速的得到结果。本人通过事件调度和存储过程模拟了物化视图。很简单,select count(*) from user where age=18; 如果是传统概念... 阅533 转1 评0 公众公开 15-06-30 14:54 |
十四复杂内连接查询复杂的内连接查询是在基本的内连接查询的基础上再附加一些查询条件,如:SELECT a.name,a.address,a.date,b.chinese,b.math,b.english FROM tb_demo065 AS a INNER JOIN tb_demo065_tel AS b on a.id=b.id WHERE b.id=(SELECT id FROM tb_demo065 WHERE tb_demo065.name=''$_POST[text]'')总之,实现表与表... 阅15 转0 评0 公众公开 15-06-30 14:49 |
先看下explain结果: SELECT *FROM deviceback d,20130602_AppLog gWHERE d.mid=g.mid AND d.imei=g.imei AND d.mac=g.mac AND d.brands=0 AND g.coperator <>'''' limit 20;Great,不到3秒就出来结果了。SELECT d.mid,g.mac,FROM deviceback d,20130602_AppLog gWHERE d.imei=g.imei AND d.mac=... 阅31 转0 评0 公众公开 15-06-19 08:57 |
./ndb_mgm -- NDB Cluster -- Management Client -- ndb_mgm> show Connected to Management Server at: 192.168.1.251:1186 Cluster Configuration --------------------- [ndbd(NDB)] 1 node(s) id=2 @192.168.1.251 (Version:5.0.22, Nodegroup: 0, Master) [ndb_mgmd(MGM)] 1 node(s) id=1 @192.168.1.251 (Version... 阅81 转1 评0 公众公开 15-06-01 01:13 |
但是直接在 mySql workbatch 中运行是正确的!!MySql.MySqlClient.MySqlConnection mySqlConn = new MySql.MySqlCommand mySqlCmd = new MySql.CommandText = "set @rowNum:=0; create temporary table T_729540255 as ( Select @rowNum:=ifnull(@rowNum,0)+1 as Temp_id, A.employee_id,A.employee_no From employee A)"; 阅15471 转25 评0 公众公开 15-05-22 09:43 |
MySQL定时执行脚本(计划任务)命令实例。CREATE EVENT e_testON SCHEDULE EVERY 1 DAYSTARTS CURRENT_TIMESTAMP + INTERVAL 5 DAYENDS CURRENT_TIMESTAMP + INTERVAL 1 MONTHDO TRUNCATE TABLE test.aaa;修改事件(ALTER EVENT)ALTER EVENT event_name[ON SCHEDULE schedule][RENAME TO new_event_name][ON COMPLETION [NOT] PRESERVE][COMMENT &... 阅25 转0 评0 公众公开 15-05-20 10:43 |
MySQL Date/Time to Str(日期/时间转换为字符串)函数:date_format(date,format), time_format(time,format)+-------------------------------------+| time_format(''22:23:01'', ''%H.%i.%s'') |+-------------------------------------+| 22.23.01 |+-------------------------------------+MySQL 日期、... 阅21 转0 评0 公众公开 15-05-20 09:28 |
delimiter // CREATE PROCEDURE useCursor() BEGIN DECLARE oneAddr varchar(8) default '''';DECLARE CONTINUE HANDLER FOR SQLSTATE ''02000'' SET oneAddr = null;FETCH curl INTO oneAddr;WHILE(oneAddr is not null) DO set oneAddr = CONCAT(oneAddr, '';set allAddr = CONCAT(... 阅160 转2 评0 公众公开 15-05-19 15:53 |
阅606 转0 评0 公众公开 15-05-19 15:15 |