尽管您无法使用单个查询进行操作，但是可以使用存储过程进行操作…唯一的先决条件是，您需要在现有示例表中再添加2条记录，以表示“ C1”和“ C2” ARE顶层…添加一条记录，其中“父级”字段为空白，子级为“ C1”，另一级为“ C2”。这将“准备”最上层的父级。进行后续层次结构关联，否则您将没有顶层层次结构的起始“基础”。它还需要一个“主键”列（我在此脚本中将其创建为“ IDMyTable”，它只是1-x顺序的，但是假设您在表上有一个自动增量列可以代替使用）。
我已经包括了所有输出列以显示其构建方式，但是此例程的前提是根据预期的列输出创建表，但还要额外保留一些层次表示形式，以供构建时使用。为了确保它们在层变得更深时保持正确的方向，我在“ ID”列中加上了“ ID”列-您将看到它在最终结果集中的工作方式。
然后，在最终结果集中，我将根据层次结构数据的深度填充空白。
循环将基于在上一个结果集中找到的父记录添加任何记录，但前提是尚未添加ID（防止重复记录）…
要查看循环顺序是如何不断添加的，您可以运行不带该顺序的最后一个查询，并查看每个迭代如何限定条件并添加上一个层次结构级别…
-- --------------------------------------------------------------------------------
-- Routine DDL
-- Note: comments before and after the routine body will not be stored by the server
-- --------------------------------------------------------------------------------
DELIMITER $$
CREATE DEFINER=`root`@`localhost` PROCEDURE `GetHierarchy2`()
BEGIN
-- prepare a hierarchy level variable
set @hierlvl := 00000;
-- prepare a variable for total rows so we kNow when no more rows found
set @lastRowCount := 0;
-- pre-drop temp table
drop table if exists MyHierarchy;
-- Now, create it as the first level you want...
-- ie: a specific top level of all "no parent" entries
-- or parameterize the function and ask for a specific "ID".
-- add extra column as flag for next set of ID's to load into this.
create table MyHierarchy as
select
t1.IDMyTable,
t1.Child AS Parent,
@hierlvl as IDHierLevel,
cast( t1.IDMyTable as char(100)) FullHierarchy
from
MyTable t1
where
t1.Parent is null
OR t1.Parent = '';
-- how many rows are we starting with at this tier level
set @lastRowCount := ROW_COUNT();
-- we need to have a "primary key", otherwise our UPDATE
-- statement will nag about an unsafe update command
alter table MyHierarchy add primary key (IDMyTable);
-- Now, keep cycling through until we get no more records
while @lastRowCount > 0 do
-- Now, load in all entries found from full-set NOT already processed
insert into MyHierarchy
select
t1.IDMyTable,
t1.Child as Parent,
h1.IDHierLevel +1 as IDHierLevel,
concat_ws( ',', h1.FullHierarchy, t1.IDMyTable ) as FullHierarchy
from
MyTable t1
join MyHierarchy h1
on t1.Parent = h1.Parent
left join
MyHierarchy h2
on t1.IDMyTable = h2.IDMyTable
where
h2.IDMyTable is null;
set @lastRowCount := row_count();
-- Now, update the hierarchy level
set @hierLevel := @hierLevel +1;
end while;
-- return the final set Now
select
*, concat( lpad( ' ', 1 + (IDHierLevel * 3 ), ' ' ), Parent ) as ShowHierarchy
from MyHierarchy
order by FullHierarchy;
END
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