Mysql parent-child structure sorting _ MySQL

Mysql parent-child structure sorting projects often encounter parent-child structure display problems. different databases have different write methods, such as using with union in SqlServer, while Mysql does not have such convenient statements.

In the following category table, foods include pizaa, buger, and coffee, while pizza is divided into several types of cheese. how can they express their parent-child structure?

CREATE TABLE category(    id INT(10),    parent_id INT(10),    name VARCHAR(50));INSERT INTO category (id, parent_id, name) VALUES(1, 0, 'pizza'),        --node 1(2, 0, 'burger'),       --node 2(3, 0, 'coffee'),       --node 3(4, 1, 'piperoni'),     --node 1.1(5, 1, 'cheese'),       --node 1.2(6, 1, 'vegetariana'),  --node 1.3(7, 5, 'extra cheese'); --node 1.2.1

One person on stackoverflow gave a good solution:

1. create a function

Delimiter ~ Drop function getPriority ~ Create function getPriority (inID INT) returns varchar (255) DETERMINISTICbegin DECLARE gParentID int default 0; DECLARE gPriority VARCHAR (255) DEFAULT ''; SET gPriority = inID; SELECT parent_id INTO gParentID FROM category where id = inID; WHILE gParentID> 0 DO/* 0 is the root */SET gPriority = CONCAT (gParentID ,'. ', gPriority); SELECT parent_id INTO gParentID FROM category where id = gParentID; end while; RETURN gPriority; end ~ Delimiter;

2. the result of calling the function is the result of sorting out the order.

SELECT * FROM category ORDER BY getPriority(ID);

☆The restriction of the getPriority function is that all data tracing must have a unique ancestor. The tree structure cannot contain multiple trees.