如何重新计算GROUP上的字段

Question

我有一张桌子

f1|f2|fk
1 | 0|100
1 | 1|200
1 | 2|300
1 | 3|400
2 | 0|300
2 | 1|400
2 | 2|500

(f1,f2)PK和fk 在哪里是外键.fk的值不多,约为20. f2永远不会超过3. (f1,f2)然而,有很多对.(f1,fk)是UNIQUE.

现在,假设我们将100和200映射到A,300和400映射到B,500到C - 这个映射是给定的.我们想(f1_new,fk_mapped)留下来UNIQUE.到目前为止,这已经大致解决了

INSERT INTO mapped (f1_new,f2_new,fk_new)
SELECT f1, MIN(f2), CASE fk WHEN 100 THEN A WHEN 200 THEN A END AS fk
FROM origin
GROUP BY f1, fk

现在,问题是我们需要在映射表中保持f2值0,1,2,所以这是期望的结果:

f1_new|f2_new|fk_mapped
1     | 0    |A
1     | 1    |B
2     | 0    |B
2     | 1    |C

我真的想在MySQL中保留它.

Answer 1

我认为应该这样做：

INSERT INTO mapped (f1_new, f2_new, fk_new)
SELECT f1_new, f2_new, fk_new from (
    SELECT f1_new, @f2 := if(f1_new = @prev_f1, @f2+1, 0) f2_new, fk_new, @prev_f1 := f1_new
    FROM (select f1 AS f1_new, CASE WHEN fk IN (100, 200) THEN 'A'
                                    WHEN fk in (300, 400) THEN 'B'
                                    WHEN fk = 500 THEN 'C'
                               END AS fk_new
          FROM origin
          GROUP BY f1_new, fk_new
          ORDER BY f1_new, fk_new) new,
         (SELECT @f2 := NULL, @prev_f1 := NULL) vars
    ) x

小提琴