[英]Get percentage based on value in previous row
對於給定的數據:
+---+--------+------+
|CID| number | rum |
+---+--------+------+
| 1 | 1.0000 | NULL |
| 3 | 2.0000 | NULL |
| 5 | 2.0000 | NULL |
| 6 | 4.0000 | NULL |
+---+--------+------+
我想用當前和以前數字的百分比變化來計算朗姆酒。
rum = (currNumber - prevNumber) / prevNumber * 100
預期結果:
+---+--------+------+
|CID| number | rum |
+---+--------+------+
| 1 | 1.0000 | NULL |
| 3 | 2.0000 |100.0 |
| 5 | 2.0000 | 0.0 |
| 6 | 4.0000 |100.0 |
+---+--------+------+
LAG
function 在 MySQL 中不起作用。
假設行是根據 CID 排序的,您可以使用相關子查詢找到前一行:
SELECT CID, number, (
SELECT (c.number - p.number) / p.number * 100
FROM t AS p
WHERE p.CID < c.CID
ORDER BY p.CID DESC
LIMIT 1
) AS rum
FROM t AS c
您可以使用變量模擬lag()
:
set @num = null;
select
cid,
number,
(number- lag_number)/lag_number * 100 rum
from (
select
cid,
@num lag_number,
@num := number number
from mytable
order by cid
) t
order by cid
cid | number | rum --: | -----: | ---: 1 | 1.0000 | null 3 | 2.0000 | 100 5 | 2.0000 | 0 6 | 4.0000 | 100
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