Question

我想更新一个名为ratio的字段。对于比率，我想从我从此查询中获得的两个值计算它。

/*Returns the sum of the latest two entries in two different rows*/
select sum(value) as sum from db.s s
where s.r_id = 76703
group by timeIn
order by timeIn DESC
LIMIT 2;
/*calculate ratio??*/
UPDATE db.r SET ratio = RESULT??

上面的查询给出了两行有两个值比率应为row1 / row2 然后更新另一个表上的比率字段。

Answer 1

我几乎可以肯定这个问题有一种更高效，更清洁的解决方案。但是，这也可能有效。

UPDATE db.r SET ratio = 
(
 select sum(value) as sum from db.s s
 where s.r_id = 76703
 group by timeIn
 order by timeIn DESC
 LIMIT 1;
)
/
(
 select sum(value) as sum from db.s s
 where s.r_id = 76703
 group by timeIn
 order by timeIn DESC
 LIMIT 1,1;
)

Answer 2

您可以排名，并使用CASE获取这两个值;

UPDATE r SET ratio = (
  SELECT SUM(CASE WHEN c=2 THEN sum ELSE 0 END) /
         SUM(CASE WHEN c=1 THEN sum ELSE 0 END)
  FROM (
    SELECT SUM(value) sum, @c:=@c+1 c
    FROM s, (SELECT @c:=0)a
    WHERE s.r_id = 76703
    GROUP BY timeIn
    ORDER BY timeIn 
    LIMIT 2
  )z
);

An SQLfiddle to test with

MYSQL Update值来自查询结果的划分

2 个答案: