数据库如何连接三个表

相对最优：

SELECT ASSETCHANGEAPPLYINFO.*,ASSETCHANGEINFO.OPERATION

               FROM

                    ASSETCHANGEINFO_ASSETCHANGEAPPLYINFO

                    INNER JOIN ASSETCHANGEAPPLYINFO ON ASSETCHANGEINFO_ASSETCHANGEAPPLYINFO.ASSET_CHANGE_APPLYINFO_ID = ASSETCHANGEAPPLYINFO.ID

                   LEFT JOIN ASSETCHANGEINFO ON ASSETCHANGEINFO_ASSETCHANGEAPPLYINFO.ASSET_CHANGEINFO_ID=ASSETCHANGEINFO.ID

 

 另外的方法：

SELECT a.*, ASSETCHANGEINFO.OPERATION

               FROM (

                    SELECT * FROM   ASSETCHANGEINFO_ASSETCHANGEAPPLYINFO

                    INNER JOIN ASSETCHANGEAPPLYINFO ON ASSETCHANGEINFO_ASSETCHANGEAPPLYINFO.ASSET_CHANGE_APPLYINFO_ID = ASSETCHANGEAPPLYINFO.ID) AS a

                    LEFT JOIN ASSETCHANGEINFO ON a.ASSET_CHANGEINFO_ID=ASSETCHANGEINFO.ID

 

 SELECT        ASSETCHANGEAPPLYINFO.*,ASSETCHANGEINFO.OPERATION

               FROM

                    ASSETCHANGEINFO_ASSETCHANGEAPPLYINFO,ASSETCHANGEAPPLYINFO,ASSETCHANGEINFO

                   WHERE ASSETCHANGEINFO_ASSETCHANGEAPPLYINFO.ASSET_CHANGE_APPLYINFO_ID = ASSETCHANGEAPPLYINFO.ID

                   AND ASSETCHANGEINFO_ASSETCHANGEAPPLYINFO.ASSET_CHANGEINFO_ID=ASSETCHANGEINFO.ID