MySql:父级和子级ORDER BY [英] MySql: ORDER BY parent and child

问题描述

我有一张桌子，像这样:

I have a table like:

+------+---------+-
| id   | parent  |
+------+---------+
| 2043 |    NULL |
| 2044 |    2043 |
| 2045 |    2043 |
| 2049 |    2043 |
| 2047 |    NULL |
| 2048 |    2047 |
| 2043 |    2047 |
+------+---------+

展示了一个简单的两级父子" -corelation.我如何通过SELECT语句进行排序来获得如上列表中所示的顺序，这意味着:第一亲，第二亲，第二亲，第二亲等等(如果我有的话，我可以添加为孩子们订购订单...我希望).是否可以添加排序字段?

which shows a simple, 2-level "parent-child"-corelation. How can I ORDER BY an SELECT-statement to get the order like in the list above, which means: 1st parent, childs of 1st parent, 2nd parent, childs of 2nd parent and so on (if I have that, I can add the ORDER BYs for the children... I hope). Is it possible withoug adding a sort-field?

推荐答案

包括按ID对子级进行排序:

Including sorting children by id:

ORDER BY COALESCE(parent, id), parent IS NOT NULL, id

SQL小提琴示例

说明:

• COALESCE(parent, id):首先按(有效分组)父母的ID排序.
• parent IS NOT NULL:将父行放在组的顶部
• id:最后对所有子级进行排序(父级相同，并且parent不为空)

• COALESCE(parent, id): First sort by (effectively grouping together) the parent's id.
• parent IS NOT NULL: Put the parent row on top of the group
• id: Finally sort all the children (same parent, and parent is not null)

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