MySQL 实现树的遍历详解及简单实现示例
MySQL实现树的遍历
经常在一个表中有父子关系的两个字段，比如empno与manager，这种结构中需要用到树的遍历。在Oracle中可以使用connectby简单解决问题，但MySQL5.1中还不支持（据说已纳入todo中），要自己写过程或函数来实现。
一、建立测试表和数据：
DROPTABLEIFEXISTS`channel`; CREATETABLE`channel`( `id`int(11)NOTNULLAUTO_INCREMENT, `cname`varchar(200)DEFAULTNULL, `parent_id`int(11)DEFAULTNULL, PRIMARYKEY(`id`) )ENGINE=MyISAMAUTO_INCREMENT=19DEFAULTCHARSET=utf8; /*Dataforthetable`channel`*/ insertinto`channel`(`id`,`cname`,`parent_id`) values(13,'首页',-1), (14,'TV580',-1), (15,'生活580',-1), (16,'左上幻灯片',13), (17,'帮忙',14), (18,'栏目简介',17);
二、利用临时表和递归过程实现树的遍历（MySQL的UDF不能递归调用）：
DELIMITER$$ USE`db1`$$ --从某节点向下遍历子节点 --递归生成临时表数据 DROPPROCEDUREIFEXISTS`createChildLst`$$ CREATEPROCEDURE`createChildLst`(INrootIdINT,INnDepthINT) BEGIN DECLAREdoneINTDEFAULT0; DECLAREbINT; DECLAREcur1CURSORFORSELECTidFROMchannelWHEREparent_id=rootId; DECLARECONTINUEHANDLERFORNOTFOUNDSETdone=1; SETmax_sp_recursion_depth=12; INSERTINTOtmpLstVALUES(NULL,rootId,nDepth); OPENcur1; FETCHcur1INTOb; WHILEdone=0DO CALLcreateChildLst(b,nDepth+1); FETCHcur1INTOb; ENDWHILE; CLOSEcur1; END$$ --从某节点向上追溯根节点 --递归生成临时表数据 DROPPROCEDUREIFEXISTS`createParentLst`$$ CREATEPROCEDURE`createParentLst`(INrootIdINT,INnDepthINT) BEGIN DECLAREdoneINTDEFAULT0; DECLAREbINT; DECLAREcur1CURSORFORSELECTparent_idFROMchannelWHEREid=rootId; DECLARECONTINUEHANDLERFORNOTFOUNDSETdone=1; SETmax_sp_recursion_depth=12; INSERTINTOtmpLstVALUES(NULL,rootId,nDepth); OPENcur1; FETCHcur1INTOb; WHILEdone=0DO CALLcreateParentLst(b,nDepth+1); FETCHcur1INTOb; ENDWHILE; CLOSEcur1; END$$ --实现类似OracleSYS_CONNECT_BY_PATH的功能 --递归过程输出某节点id路径 DROPPROCEDUREIFEXISTS`createPathLst`$$ CREATEPROCEDURE`createPathLst`(INnidINT,INdelimitVARCHAR(10),INOUTpathstrVARCHAR(1000)) BEGIN DECLAREdoneINTDEFAULT0; DECLAREparentidINTDEFAULT0; DECLAREcur1CURSORFOR SELECTt.parent_id,CONCAT(CAST(t.parent_idASCHAR),delimit,pathstr) FROMchannelAStWHEREt.id=nid; DECLARECONTINUEHANDLERFORNOTFOUNDSETdone=1; SETmax_sp_recursion_depth=12; OPENcur1; FETCHcur1INTOparentid,pathstr; WHILEdone=0DO CALLcreatePathLst(parentid,delimit,pathstr); FETCHcur1INTOparentid,pathstr; ENDWHILE; CLOSEcur1; END$$ --递归过程输出某节点name路径 DROPPROCEDUREIFEXISTS`createPathnameLst`$$ CREATEPROCEDURE`createPathnameLst`(INnidINT,INdelimitVARCHAR(10),INOUTpathstrVARCHAR(1000)) BEGIN DECLAREdoneINTDEFAULT0; DECLAREparentidINTDEFAULT0; DECLAREcur1CURSORFOR SELECTt.parent_id,CONCAT(t.cname,delimit,pathstr) FROMchannelAStWHEREt.id=nid; DECLARECONTINUEHANDLERFORNOTFOUNDSETdone=1; SETmax_sp_recursion_depth=12; OPENcur1; FETCHcur1INTOparentid,pathstr; WHILEdone=0DO CALLcreatePathnameLst(parentid,delimit,pathstr); FETCHcur1INTOparentid,pathstr; ENDWHILE; CLOSEcur1; END$$ --调用函数输出id路径 DROPFUNCTIONIFEXISTS`fn_tree_path`$$ CREATEFUNCTION`fn_tree_path`(nidINT,delimitVARCHAR(10))RETURNSVARCHAR(2000)CHARSETutf8 BEGIN DECLAREpathidVARCHAR(1000); SET@pathid=CAST(nidASCHAR); CALLcreatePathLst(nid,delimit,@pathid); RETURN@pathid; END$$ --调用函数输出name路径 DROPFUNCTIONIFEXISTS`fn_tree_pathname`$$ CREATEFUNCTION`fn_tree_pathname`(nidINT,delimitVARCHAR(10))RETURNSVARCHAR(2000)CHARSETutf8 BEGIN DECLAREpathidVARCHAR(1000); SET@pathid=''; CALLcreatePathnameLst(nid,delimit,@pathid); RETURN@pathid; END$$ --调用过程输出子节点 DROPPROCEDUREIFEXISTS`showChildLst`$$ CREATEPROCEDURE`showChildLst`(INrootIdINT) BEGIN DROPTEMPORARYTABLEIFEXISTStmpLst; CREATETEMPORARYTABLEIFNOTEXISTStmpLst (snoINTPRIMARYKEYAUTO_INCREMENT,idINT,depthINT); CALLcreateChildLst(rootId,0); SELECTchannel.id,CONCAT(SPACE(tmpLst.depth*2),'--',channel.cname)NAME,channel.parent_id,tmpLst.depth,fn_tree_path(channel.id,'/')path,fn_tree_pathname(channel.id,'/')pathname FROMtmpLst,channelWHEREtmpLst.id=channel.idORDERBYtmpLst.sno; END$$ --调用过程输出父节点 DROPPROCEDUREIFEXISTS`showParentLst`$$ CREATEPROCEDURE`showParentLst`(INrootIdINT) BEGIN DROPTEMPORARYTABLEIFEXISTStmpLst; CREATETEMPORARYTABLEIFNOTEXISTStmpLst (snoINTPRIMARYKEYAUTO_INCREMENT,idINT,depthINT); CALLcreateParentLst(rootId,0); SELECTchannel.id,CONCAT(SPACE(tmpLst.depth*2),'--',channel.cname)NAME,channel.parent_id,tmpLst.depth,fn_tree_path(channel.id,'/')path,fn_tree_pathname(channel.id,'/')pathname FROMtmpLst,channelWHEREtmpLst.id=channel.idORDERBYtmpLst.sno; END$$ DELIMITER;
三、测试
CALLshowChildLst(-1); CALLshowChildLst(13); CALLshowChildLst(14); CALLshowChildLst(17); CALLshowChildLst(18); CALLshowParentLst(-1); CALLshowParentLst(13); CALLshowParentLst(14); CALLshowParentLst(17); CALLshowParentLst(18);
四、遗留问题
1.因为mysql对动态游标的支持不够，所以要想做成通用的过程或函数比较困难，可以利用两个临时表来转换（同时去掉了递归调用）是个相对通用的实现。
2.目前来看无论哪种实现，效率都不太好，希望mysql自己能实现Oracle的connectby功能，应该会比较优化。
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