LeetCode（数据库）- 树节点

--解决方案(1)
SELECTid, 'Root'ASTypeFROMtreeWHEREp_idISNULLUNIONSELECTid, 'Leaf'ASTypeFROMtreeWHEREidNOTIN (SELECTDISTINCTp_idFROMtreeWHEREp_idISNOTNULL)
ANDp_idISNOTNULLUNIONSELECTid, 'Inner'ASTypeFROMtreeWHEREidIN (SELECTDISTINCTp_idFROMtreeWHEREp_idISNOTNULL)
ANDp_idISNOTNULLORDERBYid;
--解决方案(2)
SELECTidAS`Id`,
CASEWHENtree.id= (SELECTatree.idFROMtreeatreeWHEREatree.p_idISNULL)
THEN'Root'WHENtree.idIN (SELECTatree.p_idFROMtreeatree)
THEN'Inner'ELSE'Leaf'ENDASTypeFROMtreeORDERBY`Id`;
--解决方案(3)
SELECTatree.id,
IF(ISNULL(atree.p_id),
'Root',
IF(atree.idIN (SELECTp_idFROMtree), 'Inner','Leaf')) TypeFROMtreeatreeORDERBYatree.id;
--解决方案(4)
SELECTDISTINCTt1.id, IF(t1.p_idISNULL, "Root", IF(t2.idISNOTNULL, "Inner", "Leaf")) TypeFROMtreet1LEFTJOINtreet2ONt1.id=t2.p_id;