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',12,19,8,0,0,1), ('B',12,11,12,NULL,NULL,2), ('C',5,6,4,NULL,NULL,3), ('D',3,6,3,NULL,NULL,4), ('E',4,6,3,NULL,NULL,5), ('F',4,6,4,NULL,NULL,6), ('G',3,6,3,NULL,NULL,7), ('H',5,6,5,NULL,NULL,8), ('I',7,6,7,NULL,NULL,9), ('J',12,9,12,NULL,NULL,10) ('K',12,24,8,NULL,NULL,11), ('L',5,16,3,NULL,NULL,12), ('M',7,16,7,NULL,NULL,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",cols,"rows","minItemCols",x,y,rn) VALUES ('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',12,9,12,0,48,10) ('K',12,24,8,0,57,11), ('L',5,16,3,0,81,12), ('M',7,16,7,5,81,13);
For rn (row number) = 1, x and y always stays as 0. Now I need to update the rest of x and y columns based on the above scenario(IF ..ELSE). I am unable to update the next row without updating the previous row. Is there a way to do this in a query
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Answer
You can use a recursive CTE for this type of query:
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 ;
updates the table to
+----+----+----+-----------+----+----+--+ |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| +----+----+----+-----------+----+----+--+
Note that the results are slightly different from your example from row “K” onward. I think "row J".x
should be 7
not 0
(from the last else if
condition), which changes the rest of the rows too. Still, I think it should be pretty easy to adapt the code to get the results you want.