问题描述
CREATE TABLE xyz (name text,cols int,rows int,minitemcols int,x int,y int,rn int);
INSERT INTO xyz ("widgetName",cols,"rows","minItemCols",x,y,rn) VALUES
('A',12,19,8,1),('B',11,NULL,2),('C',5,6,4,3),('D',3,4),('E',5),('F',6),('G',7),('H',8),('I',7,9),('J',9,10)
('K',24,11),('L',16,12),('M',13);
-- x
IF (CurrentRow.cols + CurrentRow.x = 12) || (CurrentRow.cols + CurrentRow.x = NextRow.minItemCols) THEN
NextRow.x = 0
ELSE IF (CurrentRow.cols + CurrentRow.x < 12) && (CurrentRow.cols + CurrentRow.x >= NextRow.minItemCols)
NextRow.x = CurrentRow.cols + CurrentRow.x
ELSE IF (CurrentRow.cols + CurrentRow.x < 12)
NextRow.x = CurrentRow.cols + CurrentRow.x
END IF;
--y
IF (CurrentRow.cols + CurrentRow.x = 12) THEN
NextRow.y = CurrentRow.rows + CurrentRow.y
ELSE IF (CurrentRow.cols + CurrentRow.x < 12)
NextRow.y = CurrentRow.y
END IF;
-- Output (providing in insert statements)
INSERT INTO xyz ("widgetName",30,36,42,48,57,81,13);
对于 rn(行号)= 1,x 和 y 始终保持为 0。现在我需要根据上述情况(IF ..ELSE)更新 x 和 y 列的其余部分。如果不更新上一行,我将无法更新下一行。有没有办法在查询中做到这一点
解决方法
您可以对此类查询使用递归 CTE:
WITH RECURSIVE rec(name,col,row,min_item_col,x,y,rn) AS (
SELECT *
FROM xyz
WHERE rn = 1
UNION ALL
(
SELECT next.name,next.cols,next.rows,next.minitemcols,CASE
WHEN cur.col + cur.x = 12 THEN 0
WHEN cur.col + cur.x = next.minitemcols THEN 0
/* this 3rd condition seems pointless given the last one */
WHEN cur.col + cur.x < 12 AND cur.x + cur.col >= next.minitemcols THEN cur.col + cur.x
WHEN cur.col + cur.x < 12 THEN cur.col + cur.x
END AS x,CASE
WHEN cur.col + cur.x = 12 THEN cur.row + cur.y
WHEN cur.col + cur.x < 12 THEN cur.y
END AS y,next.rn
FROM rec AS cur
JOIN xyz AS next
ON next.rn > cur.rn
ORDER BY rn
LIMIT 1
)
)
UPDATE xyz
SET x = rec.x,y = rec.y
FROM rec
WHERE xyz.rn = rec.rn
;
将表更新为
+----+----+----+-----------+----+----+--+
|name|cols|rows|minitemcols|x |y |rn|
+----+----+----+-----------+----+----+--+
|A |12 |19 |8 |0 |0 |1 |
|B |12 |11 |12 |0 |19 |2 |
|C |5 |6 |4 |0 |30 |3 |
|D |3 |6 |3 |5 |30 |4 |
|E |4 |6 |3 |8 |30 |5 |
|F |4 |6 |4 |0 |36 |6 |
|G |3 |6 |3 |4 |36 |7 |
|H |5 |6 |5 |7 |36 |8 |
|I |7 |6 |7 |0 |42 |9 |
|J |12 |9 |12 |7 |42 |10|
|K |12 |24 |8 |NULL|NULL|11|
|L |5 |16 |3 |NULL|NULL|12|
|M |7 |16 |7 |NULL|NULL|13|
+----+----+----+-----------+----+----+--+
请注意,从“K”行开始,结果与您的示例略有不同。我认为 "row J".x
应该是 7
而不是 0
(来自最后一个 else if
条件),这也会改变其余的行。不过,我认为调整代码以获得您想要的结果应该很容易。