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How to implement unlimited levels of parent-child relationship query in a single sentence in MySQL
How to implement unlimited levels of parent-child relationship query in a single sentence in MySQL
In SQL Server, it is easy to use CTE expressions to query infinite levels of parent-child relationships; in versions that do not support CTE expressions, it can also be easily achieved with the help of function recursion.
In MySQL, the example of this requirement is slightly complicated. There is no query that supports recursion in MySQL, there is no table-valued function, and the function does not support recursion, so it is usually implemented with a loop, which seems awkward. Today I saw a recursive query implemented with a single statement. I have a unique idea and would like to share it.
Recommended related mysql video tutorials: "mysql tutorial"
Table structure and data
CREATE TABLE table1(id int, name varchar(10), parent_id int); INSERT table1 VALUES (1, ‘Home’, 0), (2, ‘About’, 1), (3, ‘Contact’, 1), (4, ‘Legal’, 2), (5, ‘Privacy’, 4), (6, ‘Products’, 1), (7, ‘Support’, 2);
Query all parents of id = 5
SELECT ID.level, DATA.* FROM(
SELECT
@id as _id,
( SELECT @id := parent_id
FROM table1
WHERE id = @id
) as _pid,
@l := @l+1 as level
FROM table1,
(SELECT @id := 5, @l := 0 ) b
WHERE @id > 0
) ID, table1 DATA
WHERE ID._id = DATA.id
ORDER BY level;According to this parent query method, it is easy to write a query for all children. The following query id=2 for all children
SELECT ID.level, DATA.* FROM(
SELECT
@ids as _ids,
( SELECT @ids := GROUP_CONCAT(id)
FROM table1
WHERE FIND_IN_SET(parent_id, @ids)
) as cids,
@l := @l+1 as level
FROM table1,
(SELECT @ids :=’1’, @l := 0 ) b
WHERE @ids IS NOT NULL
) id, table1 DATA
WHERE FIND_IN_SET(DATA.id, ID._ids)
ORDER BY level, idThis article explains how to make a single sentence in MySQL Realize unlimited levels of parent-child relationship query, please pay attention to the PHP Chinese website for more related content.
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