由Mchl添加：

Question

这是content表：

ContentID | CategoryID | Position | Other1 | Other2
===================================================
1         | 1          | NULL     | abcd   | efgh
2         | 1          | NULL     | abcd   | efgh
3         | 1          | NULL     | abcd   | efgh
4         | 2          | NULL     | abcd   | efgh
5         | 2          | NULL     | abcd   | efgh
6         | 2          | NULL     | abcd   | efgh

这些是我将要运行的查询：

SELECT ContentID FROM content WHERE CategoryID = 1 ORDER BY Position
SELECT ContentID FROM content WHERE CategoryID = 2 ORDER BY Position

现在我想实现向上移动，向下移动，移至顶部并移至底部函数以获取内容。我需要做的就是用数字填充Position列：

ContentID | CategoryID | Position
=================================
1         | 1          | 1
2         | 1          | 2
3         | 1          | 3
4         | 2          | 1
5         | 2          | 2
6         | 2          | 3

是否可以通过MySQL中的单个查询实现此目的？类似的东西：

UPDATE content
SET Position = <ROW_NUMBER>
WHERE CategoryID = 1
ORDER BY Position

UPDATE content
SET Position = <ROW_NUMBER>
WHERE CategoryID = 2
ORDER BY Position

Answer 1

这应该有效

update 
content,
(
  select 
  @row_number:=ifnull(@row_number, 0)+1 as new_position,
  ContentID 
  from content
  where CategoryID=1
  order by position
) as table_position
set position=table_position.new_position
where table_position.ContentID=content.ContentID;

但我更愿意先应用它，取消设置用户定义的变量

set @row_number:=0;

由Mchl添加：

你可以在这样的一个声明中做到这一点

update 
content,
(
  select 
  @row_number:=ifnull(@row_number, 0)+1 as new_position,
  ContentID 
  from content
  where CategoryID=1
  order by position
) as table_position,
(
  select @row_number:=0
) as rowNumberInit
set position=table_position.new_position
where table_position.ContentID=content.ContentID;

Answer 2

这是适用于我的解决方案（希望它可以帮助某人）：

-- The following query re-populates the "Position" column with sequential numbers so that:
-- a) sequence is reset to 1 for each "group"
-- b) sequence is based on row number relative to each group depending on how ORDER BY is specified
-- c) sequence does not disturb the original order but
-- c.a) fixes NULLs so that they are moved to top
-- c.b) fixes duplicate position values depending on how ORDER BY is specified

-- ContentID is the primary key
-- CategoryID is a foreign key
-- Position column contains relative position of a record

SET @current_group = NULL;
SET @current_count = NULL;

UPDATE 
content
SET Position = CASE
    WHEN @current_group = CategoryID THEN @current_count := @current_count + 1
    WHEN @current_group := CategoryID THEN @current_count := 1
END
ORDER BY CategoryID, Position -- <Column 3>, <Column 4>, ...

Answer 3

我认为当您对表执行某些操作时，始终运行其他查询会非常繁琐。每当你想在表格中插入/更新某些东西时，我会create trigger。

在您的情况下，建议使用BEFORE UPDATE和BEFORE INSERT触发器。如果您还想在删除etntry后保持清洁，请添加AFTER DELETE触发器。

Answer 4

初始：

UPDATE content as uc 
SET Position = (
    SELECT count(*) 
    FROM content as sc 
    WHERE sc.CategoryId = uc.CategoryId AND sc.Position is not null)
WHERE uc.Position is null
ORDER BY uc.ContentId

插入之前：

UPDATE content
SET Position = Position+1
WHERE Position >= newPos AND CategoryId = newCat

更新列以使其包含行位置

4 个答案:

由Mchl添加：