MySql分组后随机获取每组一条数据的操作
思路:先随机排序然后再分组就好了。
1、创建表:
CREATE TABLE `xdx_test` ( `id` int(11) NOT NULL, `name` varchar(255) DEFAULT NULL, `class` varchar(255) DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
2、插入数据
INSERT INTO xdx_test VALUES (1, '张三-1','1'); INSERT INTO xdx_test VALUES (2, '李四-1','1'); INSERT INTO xdx_test VALUES (3, '王五-1','1'); INSERT INTO xdx_test VALUES (4, '张三-2','2'); INSERT INTO xdx_test VALUES (5, '李四-2','2'); INSERT INTO xdx_test VALUES (6, '王五-2','2'); INSERT INTO xdx_test VALUES (7, '张三-3','3'); INSERT INTO xdx_test VALUES (8, '李四-3','3'); INSERT INTO xdx_test VALUES (9, '王五-3','3');
3、查询语句
SELECT * FROM (SELECT * FROM xdx_test ORDER BY RAND()) a GROUP BY a.class
4、查询结果
3 王五-1 1
5 李四-2 2
9 王五-3 3
3 王五-1 1
4 张三-2 2
7 张三-3 3
2 李四-1 1
5 李四-2 2
8 李四-3 3
补充知识:mysql实现随机获取几条数据的方法(效率和离散型比较)
sql语句有几种写法、效率、以及离散型 比较
1:SELECT * FROM tablename ORDER BY RAND() LIMIT 想要获取的数据条数;
2:SELECT *FROM `table` WHERE id >= (SELECT FLOOR( MAX(id) * RAND()) FROM `table` ) ORDER BY id LIMIT 想要获取的数据条数;
3:SELECT * FROM `table` AS t1 JOIN (SELECT ROUND(RAND() * (SELECT MAX(id) FROM `table`)) AS id) AS t2 WHERE t1.id >= t2.id
ORDER BY t1.id ASC LIMIT 想要获取的数据条数;
4:SELECT * FROM `table`WHERE id >= (SELECT floor(RAND() * (SELECT MAX(id) FROM `table`))) ORDER BY id LIMIT 想要获取的数据条数;
5:SELECT * FROM `table` WHERE id >= (SELECT floor( RAND() * ((SELECT MAX(id) FROM `table`)-(SELECT MIN(id) FROM `table`)) + (SELECT MIN(id) FROM `table`))) ORDER BY id LIMIT 想要获取的数据条数;
6:SELECT * FROM `table` AS t1 JOIN (SELECT ROUND(RAND() * ((SELECT MAX(id) FROM `table`)-(SELECT MIN(id) FROM `table`))+(SELECT MIN(id) FROM `table`)) AS id) AS t2 WHERE t1.id >= t2.id ORDER BY t1.id LIMIT 想要获取的数据条数;
1的查询时间>>2的查询时间>>5的查询时间>6的查询时间>4的查询时间>3的查询时间,也就是3的效率最高。
以上6种只是单纯的从效率上做了比较;
上面的6种随机数抽取可分为2类:
第一个的离散型比较高,但是效率低;其他5个都效率比较高,但是存在离散性不高的问题;
怎么解决效率和离散型都满足条件啦?
我们有一个思路就是: 写一个存储过程;
select * FROM test t1 JOIN (SELECT ROUND(RAND() * ((SELECT MAX(id) FROM test)-(SELECT MIN(id) FROM test)) + (SELECT MIN(id) FROM test)) AS id) t2 where t1.id >= t2.id limit 1
每次取出一条,然后循环写入一张临时表中;最后返回 select 临时表就OK;
这样既满足了效率又解决了离散型的问题;可以兼并二者的优点;
下面是具体存储过程的伪代码
DROP PROCEDURE IF EXISTS `evaluate_Check_procedure`; DELIMITER ;; CREATE DEFINER=`root`@`%` PROCEDURE `evaluate_Check_procedure`(IN startTime datetime, IN endTime datetime,IN checkNum INT,IN evaInterface VARCHAR(36)) BEGIN
-- 新建一张临时表 ,存放随机取出的数据
create temporary table if not exists xdr_authen_tmp ( `ID` bigint(20) NOT NULL AUTO_INCREMENT COMMENT '序号', `LENGTH` int(5) DEFAULT NULL COMMENT '字节数', `INTERFACE` int(3) NOT NULL COMMENT '接口', `XDR_ID` varchar(32) NOT NULL COMMENT 'XDR ID', `MSISDN` varchar(32) DEFAULT NULL COMMENT '用户号码', `PROCEDURE_START_TIME` datetime NOT NULL DEFAULT '0000-00-00 00:00:00' COMMENT '开始时间', `PROCEDURE_END_TIME` datetime DEFAULT NULL COMMENT '结束时间', `SOURCE_NE_IP` varchar(39) DEFAULT NULL COMMENT '源网元IP', `SOURCE_NE_PORT` int(5) DEFAULT NULL COMMENT '源网元端口', `DESTINATION_NE_IP` varchar(39) DEFAULT NULL COMMENT '目的网元IP', `DESTINATION_NE_PORT` int(5) DEFAULT NULL COMMENT '目的网元端口', `INSERT_DATE` datetime DEFAULT NULL COMMENT '插入时间', `EXTEND1` varchar(50) DEFAULT NULL COMMENT '扩展1', `EXTEND2` varchar(50) DEFAULT NULL COMMENT '扩展2', `EXTEND3` varchar(50) DEFAULT NULL COMMENT '扩展3', `EXTEND4` varchar(50) DEFAULT NULL COMMENT '扩展4', `EXTEND5` varchar(50) DEFAULT NULL COMMENT '扩展5', PRIMARY KEY (`ID`,`PROCEDURE_START_TIME`), KEY `index_procedure_start_time` (`PROCEDURE_START_TIME`), KEY `index_source_dest_ip` (`SOURCE_NE_IP`,`DESTINATION_NE_IP`), KEY `index_xdr_id` (`XDR_ID`) ) ENGINE = InnoDB DEFAULT CHARSET=utf8; BEGIN DECLARE j INT; DECLARE i INT; DECLARE CONTINUE HANDLER FOR NOT FOUND SET i = 1;
-- 这里的checkNum是需要随机获取的数据数,比如随机获取10条,那这里就是10,通过while循环来逐个获取单个随机记录;
SET j = 0; WHILE j < checkNum DO set @sqlexi = concat( ' SELECT t1.ID,t1.LENGTH,t1.LOCAL_PROVINCE,t1.LOCAL_CITY,t1.OWNER_PROVINCE,t1.OWNER_CITY,t1.ROAMING_TYPE,t1.INTERFACE,t1.XDR_ID,t1.RAT,t1.IMSI,t1.IMEI,t1.MSISDN,t1.PROCEDURE_START_TIME,t1.PROCEDURE_END_TIME,t1.TRANSACTION_TYPE,t1.TRANSACTION_STATUS,t1.SOURCE_NE_IP,t1.SOURCE_NE_PORT,t1.DESTINATION_NE_IP,t1.DESTINATION_NE_PORT,t1.RESULT_CODE,t1.EXPERIMENTAL_RESULT_CODE,t1.ORIGIN_REALM,t1.DESTINATION_REALM,t1.ORIGIN_HOST,t1.DESTINATION_HOST,t1.INSERT_DATE', ' into @ID,@LENGTH,@LOCAL_PROVINCE,@LOCAL_CITY,@OWNER_PROVINCE,@OWNER_CITY,@ROAMING_TYPE,@INTERFACE,@XDR_ID,@RAT,@IMSI,@IMEI,@MSISDN,@PROCEDURE_START_TIME,@PROCEDURE_END_TIME,@TRANSACTION_TYPE,@TRANSACTION_STATUS,@SOURCE_NE_IP,@SOURCE_NE_PORT,@DESTINATION_NE_IP,@DESTINATION_NE_PORT,@RESULT_CODE,@EXPERIMENTAL_RESULT_CODE,@ORIGIN_REALM,@DESTINATION_REALM,@ORIGIN_HOST,@DESTINATION_HOST,@INSERT_DATE ', ' FROM xdr_authen t1 JOIN (SELECT ROUND(RAND() * ((SELECT MAX(id) FROM xdr_authen)-(SELECT MIN(id) FROM xdr_authen)) + (SELECT MIN(id) FROM xdr_authen)) AS id) t2', ' WHERE t1.PROCEDURE_START_TIME >= "',startTime,'"', ' AND t1.PROCEDURE_START_TIME < "',endTime,'"',' AND t1.INTERFACE IN (',evaInterface,')', ' and t1.id >= t2.id limit 1'); PREPARE sqlexi FROM @sqlexi; EXECUTE sqlexi; DEALLOCATE PREPARE sqlexi;
-- 这里获取的记录有可能会重复,如果是重复数据,我们则不往临时表中插入此条数据,再进行下一次随机数据的获取。依次类推,直到随机数据取够为止;
select count(1) into @num from xdr_authen_tmp where id = @ID; if @num > 0 or i=1 then SET j = j; ELSE insert into xdr_authen_tmp(ID,LENGTH,LOCAL_PROVINCE,LOCAL_CITY,OWNER_PROVINCE,OWNER_CITY,ROAMING_TYPE,INTERFACE,XDR_ID,RAT,IMSI,IMEI,MSISDN,PROCEDURE_START_TIME,PROCEDURE_END_TIME,TRANSACTION_TYPE,TRANSACTION_STATUS,SOURCE_NE_IP,SOURCE_NE_PORT,DESTINATION_NE_IP,DESTINATION_NE_PORT,RESULT_CODE,EXPERIMENTAL_RESULT_CODE,ORIGIN_REALM,DESTINATION_REALM,ORIGIN_HOST,DESTINATION_HOST,INSERT_DATE) VALUES(@ID,@LENGTH,@LOCAL_PROVINCE,@LOCAL_CITY,@OWNER_PROVINCE,@OWNER_CITY,@ROAMING_TYPE,@INTERFACE,@XDR_ID,@RAT,@IMSI,@IMEI,@MSISDN,@PROCEDURE_START_TIME,@PROCEDURE_END_TIME,@TRANSACTION_TYPE,@TRANSACTION_STATUS,@SOURCE_NE_IP,@SOURCE_NE_PORT,@DESTINATION_NE_IP,@DESTINATION_NE_PORT,@RESULT_CODE,@EXPERIMENTAL_RESULT_CODE,@ORIGIN_REALM,@DESTINATION_REALM,@ORIGIN_HOST,@DESTINATION_HOST,@INSERT_DATE); SET j = j + 1; end if; SET i=0; END WHILE;
-- 最后我们将所有的随机数查询出来,以结果集的形式返回给后台
select ID,LENGTH,LOCAL_PROVINCE,LOCAL_CITY,OWNER_PROVINCE,OWNER_CITY,ROAMING_TYPE,INTERFACE,XDR_ID,RAT,IMSI,IMEI,MSISDN,PROCEDURE_START_TIME,PROCEDURE_END_TIME,TRANSACTION_TYPE,TRANSACTION_STATUS,SOURCE_NE_IP,SOURCE_NE_PORT,DESTINATION_NE_IP,DESTINATION_NE_PORT,RESULT_CODE,EXPERIMENTAL_RESULT_CODE,ORIGIN_REALM,DESTINATION_REALM,ORIGIN_HOST,DESTINATION_HOST,INSERT_DATE from xdr_authen_tmp; END; truncate TABLE xdr_authen_tmp; END ;; DELIMITER ;
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