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  • sql语句有几种写法

    sql语句有几种写法

    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。
    ---------------------
    作者:编程爱好者熊浪
    来源:CSDN
    原文:https://blog.csdn.net/xionglangs/article/details/50630758
    版权声明:本文为博主原创文章,转载请附上博文链接!

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  • 原文地址:https://www.cnblogs.com/itxiongwei/p/9958588.html
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