Mysql服务器端分页、排序

Question

您好，我在数据库中有一张表，其中包含多列，超过 20 列，它包含许多大约 200 万条记录

该表有一个主键：Col1，它也是我的表的索引 , 由于某些原因，该列的数据类型是 varchar(200)。

我正在实现服务器端分页、排序和稍后（过滤）

我遇到了性能问题，这是我的程序

DELIMITER $$

CREATE DEFINER=`master`@`%` PROCEDURE `spGetData`(
    IN  DisplayStart int ,
    IN  SortCol int ,
    IN  SortDir nvarchar(10),
    IN  Search  nvarchar(255)
)
BEGIN

        DECLARE FirstRec int;
        DECLARE LastRec int;

        SET FirstRec = DisplayStart;

            select 
               col1,col2,col3,col4,col6,col7,col8,col9,col10,col11
               col12,col13,col14,col15,col16,col17,col18,col19,col20
               col21,
                ( select count(*) from myTable) as filtered

            from myTable



order by
case When (@SortCol = 0 and @SortDir = 'asc')  then col1 end asc ,
case When (@SortCol = 0 and @SortDir = 'desc') then col1 end desc ,

case When (@SortCol = 1 and @SortDir = 'asc')  then col2 end asc ,
case When (@SortCol = 1 and @SortDir = 'desc') then col2 end desc ,

case When (@SortCol = 2 and @SortDir = 'asc')  then col3 end asc ,
case When (@SortCol = 2 and @SortDir = 'desc') then col3 end desc ,

case When (@SortCol = 3 and @SortDir = 'asc')  then col4 end asc ,
case When (@SortCol = 3 and @SortDir = 'desc') then col4 end desc ,

case When (@SortCol = 4 and @SortDir = 'asc')  then col5 end asc ,
case When (@SortCol = 4 and @SortDir = 'desc') then col5 end desc ,

case When (@SortCol = 5 and @SortDir = 'asc')  then col6 end asc ,
case When (@SortCol = 5 and @SortDir = 'desc') then col6 end desc ,

case When (@SortCol = 6 and @SortDir = 'asc')  then col7 end asc ,
case When (@SortCol = 6 and @SortDir = 'desc') then col7 end desc ,

case When (@SortCol = 7 and @SortDir = 'asc')  then col8 end asc ,
case When (@SortCol = 7 and @SortDir = 'desc') then col8 end desc ,

case When (@SortCol = 8 and @SortDir = 'asc')  then col9 end asc ,
case When (@SortCol = 8 and @SortDir = 'desc') then col9 end desc ,

case When (@SortCol = 9 and @SortDir = 'asc')  then col10 end asc ,
case When (@SortCol = 9 and @SortDir = 'desc') then col10 end desc ,

case When (@SortCol = 10 and @SortDir = 'asc')  then col11 end asc ,
case When (@SortCol = 10 and @SortDir = 'desc') then col11 end desc ,

case When (@SortCol = 11 and @SortDir = 'asc')  then col12 end asc ,
case When (@SortCol = 11 and @SortDir = 'desc') then col12 end desc ,

case When (@SortCol = 12 and @SortDir = 'asc')  then col13 end asc ,
case When (@SortCol = 12 and @SortDir = 'desc') then col13 end desc ,

case When (@SortCol = 13 and @SortDir = 'asc')  then col14 end asc ,
case When (@SortCol = 13 and @SortDir = 'desc') then col14 end desc ,

case When (@SortCol = 14 and @SortDir = 'asc')  then col15 end asc ,
case When (@SortCol = 14 and @SortDir = 'desc') then col15 end desc ,

case When (@SortCol = 15 and @SortDir = 'asc')  then col16 end asc ,
case When (@SortCol = 15 and @SortDir = 'desc') then col16 end desc ,

case When (@SortCol = 16 and @SortDir = 'asc')  then col17 end asc ,
case When (@SortCol = 16 and @SortDir = 'desc') then col17 end desc ,

case When (@SortCol = 17 and @SortDir = 'asc')  then col18 end asc ,
case When (@SortCol = 17 and @SortDir = 'desc') then col18 end desc ,

case When (@SortCol = 18 and @SortDir = 'asc')  then col19 end asc ,
case When (@SortCol = 18 and @SortDir = 'desc') then col19 end desc ,

case When (@SortCol = 19 and @SortDir = 'asc')  then col20 end asc ,
case When (@SortCol = 19 and @SortDir = 'desc') then col20 end desc ,

case When (@SortCol = 20 and @SortDir = 'asc')  then col21 end asc ,
case When (@SortCol = 20 and @SortDir = 'desc') then col21 end desc ,


                limit FirstRec,10;

    END

查询速度很慢，并且会出现缓冲区大小问题。 如果我删除 order by 子句，它会变得非常快。

所以我的问题是

1- 我怎样才能增强这个查询并使数百万行的排序变得快速？

2- 稍后我将使用 where 子句对多个列应用过滤，如何避免任何性能问题？

Answer 1

• 应该构造（concat、prepare、execute、deallocate）ORDER BY，而不是使用不能使用任何索引的巨大表达式。
• 添加INDEX(col0), INDEX(col1), ... 是可能的，但不现实，这样准备好的语句在所有21 种情况下都会很快。选择重要的，不要将其余的提供给最终用户。
• Don't use OFFSET to paginate;而是“记住你离开的地方”。
• 过滤在哪里？这可能会干扰我已经给你的提示。
• VARCHAR(200) 通常不适合 PRIMARY KEY。
• 用户能否指定对两列进行排序？过滤日期范围？其他事情？ （如果您想了解更多详情，请提供真实的SHOW CREATE TABLE。）
• 您是否对任何列进行了“规范化”？也就是说，将大的、经常重复的值移动到其他表中。