我有一张简化的表格：
id date color
----------------------
1 2012-01-01 black
2 2012-01-02 red
3 2012-01-03 red
4 2012-01-04 red
5 2012-01-05 green
现在我需要将此表中的颜色更改插入新表：
date before now
----------------------------
2012-01-02 black red
2012-01-04 red green
有人可以告诉我怎么样？
答案 0 :(得分：3)
比较第二行与上一行：
SELECT cur.date, prev.color "before", cur.color now
FROM tbl cur
LEFT JOIN tbl prev ON cur.id = prev.id + 1
WHERE cur.id > 1 -- start detecting changes from second row
AND prev.color <> cur.color
实时测试：http://sqlfiddle.com/#!2/0c146/1
修改
即使在非连续数据中也能正常工作。如果MySQL中有CTE功能，查询可能会更加简洁
create table tbl
(
id int,
date date,
color text
);
insert into tbl(id,date,color)
select 1,'2012-1-1','black' union
select 2,'2012-1-3','red' union
select 3,'2012-1-7','red' union
select 4,'2012-1-15','red' union
select 5,'2012-1-21','green' ;
set @rx = 0;
set @ry = 0;
select cur.date, prev.color as "before", cur.color as "now"
from (select *, @ry := @ry + 1 as series from tbl order by date) as cur
left join (select *, @rx := @rx + 1 as series from tbl order by date) as prev
on cur.series = prev.series + 1
where cur.series > 1
and prev.color <> cur.color
答案 1 :(得分：0)
首先，重命名color列 - ＆gt; before，然后添加now列（如果可能，default null），然后根据需要更新now列。
答案 2 :(得分：0)
如果我理解你，你需要存储过程。