mysql 7 中实现 row_number /rank/dense_rank

关于row_number/rank/dense_rank之间的区别
https://blog.csdn.net/nayi_224/article/details/79862283

mysql版本5.7.23-log

create table test_190507(part VARCHAR(50), val1 NUMERIC, val2 NUMERIC);

insert into test_190507(part, val1, val2) values (‘a’, 1, 4);
insert into test_190507(part, val1, val2) values (‘a’, 2, 3);
insert into test_190507(part, val1, val2) values (‘a’, 3, 2);
insert into test_190507(part, val1, val2) values (‘a’, 4, 1);
insert into test_190507(part, val1, val2) values (‘b’, 1, 4);
insert into test_190507(part, val1, val2) values (‘b’, 1, 3);
insert into test_190507(part, val1, val2) values (‘b’, 2, 2);

row_number

现在要实现类似oracle中的row_number() over(partition by part order by val1, val2 desc) 的功能。

select t1.*,
			 @row_number := case when @temp = t1.part then @row_number + 1 else 1 end rn,
			 @temp := t1.part tmp
  from 
(select * from test_190507 t1 order by t1.part, t1.val1, t1.val2 desc) t1,
(select @row_number := 1 row_number, @temp := '' temp) t2
;

其中rn即为结果列。

主要利用了结果集的排序以及语句的执行顺序来依次的设置变量，很基础的for循环思维。但是由于依赖了底层结果集的排序，导致一次只能生成一个排序列。在oracle中，row_number函数很可能是成批出现的，并且有完全不同的排序规则。针对这种情况，我暂时没找到了好方法。多写几个然后在关联吧。

dense_rank

select t1.*,
			 @dense_rank := case when @lag_part != t1.part then 1 when @lag_dense = t1.val1 then @dense_rank else @dense_rank + 1 end dr,
			 @lag_part := t1.part lag_part,
			 @lag_dense := t1.val1 lag_dense
  from 
(select * from test_190507 t1 order by t1.part, t1.val1) t1,
(select @dense_rank := 1 , @lag_part := '' , @lag_dense := '' ) t2
;

dr是结果列

rank

select t1.part,
	   t1.val1,
	   t1.rank
  from (
select t1.part,
			 t1.val1,
			 @row_number := case when @lag_part = t1.part then @row_number + 1  else 1 end tmp_rn,
			 @dense_rank := case when @lag_part != t1.part then 1 when @lag_flag = t1.val1 then @rank else @row_number end rank,
			 @rank := case when @lag_part != t1.part then 1 when @lag_flag = t1.val1 then @rank else @row_number end tmp_rk,
			 @lag_part := t1.part lag_part,
			 @lag_flag := t1.val1 lag_flag
  from 
(select * from test_190507 t1 order by t1.part, t1.val1) t1,
(select @row_number := 1, @lag_part := '' , @lag_flag := '', @rank := 1 ) t2
) t1
;

听说mysql8添加了不少语法，已经支持分析函数了，甚至连递归with都支持了，尽量快点升级版本吧，这东西写着太烦。