sql新招

SELECT a.CT_ID, a.CT_Name, a.CT_ParentID, IF (a.CT_ParentID =0, '根课程', SELECT b.CT_Name FROM Course_Tree AS b WHERE b.CT_ID = a.CT_ParentID)) AS CT_ParentName, a.CT_State, a.CT_Level, a.CT_Time FROM Course_Tree AS a WHERE a.CT_ID =4

if用法跟excel里一样， if (a, b, c) 表示 a为真返回b, 否则返回c