[英]Mysql: update current value if previous row are same with current row
How do i update current row value if my previous row are same with current row. 如果上一行与当前行相同,如何更新当前行值。
the curent row is 68, previous row is also 68.. i would i like to update current row become 68-20 which is 48. 当前行是68,上一行也是68 ..我想将当前行更新为68-20,即48。
same for 98-20 = 78. 对于98-20 = 78则相同。
so that the corrected data will look like: 这样校正后的数据将如下所示:
i have more than 1000 record like this, which cant update the record one by one manually. 我有1000多个这样的记录,无法手动一次更新记录。
update table1 set DIH_QTY_BALANCE=DIH_QTY_BALANCE-DIH_REORDER_QTY
WHERE how to put the previous row same as current on where clause?
在where子句中,如何将上一行与当前行相同?
Here is the Schema + data: http://pastebin.com/T1tYDT6Y 这是Schema +数据: http : //pastebin.com/T1tYDT6Y
too large for sqlfiddle. 对于sqlfiddle太大。
any help would be great. 任何帮助都会很棒。
As far as I remember, MySQL has problems to select from the same table in an update statement. 据我所知,MySQL在更新语句中无法从同一表中进行选择。 And this is what you would have to do, because in order to update a record or not, you'd have to select its previous record from the same table.
这就是您要做的,因为要更新记录或不更新记录,您必须从同一表中选择其先前的记录。
So create a temporary table, give it row numbers, then select from it with a self join, to compare each record with its previous record. 因此,创建一个临时表,为其指定行号,然后通过自连接从中选择表,以将每个记录与其先前的记录进行比较。
create temporary table temp
(
rownum int,
dihistoryid int,
dih_qty_balance int
) engine = memory;
set @num = 0;
insert into temp
select
@num := @num + 1 as rownum,
dihistoryid,
dih_qty_balance
from mytable
order by dihistoryid;
update mytable
set dih_qty_balance = dih_qty_balance - dih_reorder_qty
where dihistoryid in
(
select current.dihistoryid
from temp current
join temp previous on previous.rownum = current.rownum - 1
where previous.dih_qty_balance = current.dih_qty_balance
);
drop temporary table temp;
May be something like this 可能是这样的
SELECT DIH_QTY_BALANCE,
(SELECT DIH_QTY_BALANCE FROM example e2
WHERE e2.DIHISTORYID < e1.DIHISTORYID
ORDER BY DIHISTORYID DESC LIMIT 1) as previous_value,
(SELECT value FROM example e3
WHERE e3.DIHISTORYID > e1.DIHISTORYID
ORDER BY DIHISTORYID ASC LIMIT 1) as next_value
FROM example e1
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