自连接：自己的表和自己的表连接
核心：把一张表拆分成两张一样的表即可
-- 查询父子信息
SELECT categoryName AS '父栏目', categoryName AS '子栏目'
from category AS a, category AS b
where a.categoryid = b.pid
标签：category,栏目,categoryName,练习,查询,联表,连接 From： https://www.cnblogs.com/gss01/p/16652371.html
自连接：自己的表和自己的表连接
核心：把一张表拆分成两张一样的表即可
-- 查询父子信息
SELECT categoryName AS '父栏目', categoryName AS '子栏目'
from category AS a, category AS b
where a.categoryid = b.pid
标签：category,栏目,categoryName,练习,查询,联表,连接 From： https://www.cnblogs.com/gss01/p/16652371.html