数据库树形结构怎么查 四种方法解决

1.使SQL实现树形查询

1.1 树形结构固定，即固定几层结构，可以采用数据库连接查询，这里以两张表为例：

select one.id, one.label, two.id, two.labelfrom course_category one inner join course_category two on two.parentid = one.idwhere one.parentid = '1'and one.is_show = '1'and two.is_show = '1'order by one.orderby, two.orderby

2.2 树形结构可能变化，采用数据库的递归进行查询

with recursive t1 as (select *from course_categorywhere id = '1'union allselect t2.*from course_category t2 inner join t1 on t2.parentid = t1.id)select *from t1order by t1.id, t1.orderby;

2.Java代码实现

1.递归查询数据库

public List findMenu(long parentID) {QueryWrapper queryWrapper = new QueryWrapper();//查询条件queryWrapper.eq("parentid", parentID);//这里传入的值为父节点的id，比如第一次进入网页这里一定是根节点的id 如果点击展开的话就是要展开节点的id 即子节点的父idList list = baseMapper.selectList(queryWrapper);for (Menu menu : list) {//递归子类数据menu.setChildMenu(findMenu(menu.getID()));}return list;}

2.一次性全部查询出来，用Java代码实现数据的树形分解

public class TreeDemo{ public static void main(String[] args) {List treeList = init();List collect = treeList.stream().filter(item -> item.getPid() == 0)//构造最外层节点，即id=0的节点.map(item -> {item.setChildrenList(getChildren(item, treeList));//id=0的节点就为他设置孩子节点return item;}).collect(Collectors.toList());System.out.println(new Gson().toJsonTree(collect));}//获得孩子节点private static List getChildren(TreeEntity treeEntity, List treeEntityList) {List collect = treeEntityList.stream().filter(item -> item.getPid().equals(treeEntity.getId()))//判断当前节点的父id是不是要设置节点的id.map(item -> {item.setChildrenList(getChildren(item, treeEntityList));//如果是 为其设置孩子节点 通过递归 为每个除了最外层节点的节点设置孩子节点return item;}).collect(Collectors.toList());return collect;} }

注：以上Java代码粘贴自网络