[英]How can this sql grouped query be corrected? (I think this is sql generic, we use postgresql)
Data set example is as follows: 数据集示例如下:
noteid seq notebalance 1 4 125.00 1 3 120.00 2 8 235.00 2 6 235.00 2 5 200.00 3 9 145.00 4 17 550.00 4 16 550.00 4 14 500.00 4 12 450.00 4 10 400.00 ...
so we basically have the latest notebalance at the beginning of each noteid group. 因此我们基本上在每个noteid组的开头都有最新的notebalance。
What is the proper sql syntax to obtain the latest balances for each noteid? 什么是正确的SQL语法,以获得每个noteid的最新余额?
as in: 如:
1 4 125.00 2 8 235.00 3 9 145.00 4 17 550.00
A generic (= ANSI SQL) solution would be to use a window function: 通用(= ANSI SQL)解决方案是使用窗口函数:
select noteid, seq, notebalance
from (
select noteid, seq, notebalance,
row_number() over (partition by noteid order by seq desc) as rn
from the_table
) t
where rn = 1
order by noteid;
When using Postgres, it's usually faster to use the distinct on
operator: 当使用Postgres时,通常使用
distinct on
运算符更快:
select distinct on (noteid) noteid, seq, notebalance
from the_table
order by noteid, seq desc;
SQLFiddle example: http://sqlfiddle.com/#!15/8ca27/2 SQLFiddle示例: http ://sqlfiddle.com/#!15/8ca27/2
I think ROW_NUMBER() is what you are looking for. 我认为ROW_NUMBER()是您要寻找的。 This is similar to this SO question .
这类似于该SO问题 。
"the record with the highest seq" := "there is no record with a higher seq (for this noteid
)" “ seq最高的记录”:=“没有更高的seq记录(对于此
noteid
)”
SELECT noteid, seq, notebalance
FROM the_table tt
WHERE NOT EXISTS (
SELECT * FROM the_table nx
WHERE nx.noteid = tt.noteid
AND nc.seq > tt.seq
)
ORDER BY noteid
;
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