如何使用行计数

Question

我想重新排序显示列，以便顺序顺序且没有间隙。类似于以下可能的

UPDATE foo
INNER JOIN bar ON foo.barid = bar.id 
SET foo.display = !rowcount!
WHERE bar.baz = 1
ORDER BY foo.display;

Answer 1

你想要这个吗？

UPDATE foo
INNER JOIN (
    SELECT t2.id, @rowNo := @rowNo + 1 AS rowcount
    FROM foo t1
    INNER JOIN bar t2 ON t1.barid = t2.id
    INNER JOIN (SELECT @rowNo := 0) t
    WHERE t2.baz = 1
    ORDER BY t1.display) bar ON foo.barid = bar.id 
SET foo.display = bar.rowcount