Given a specified index set {C1,C2,C3}, we construct the SQL as follows:"SELECT C1,C2 FROM T1 JOIN T2 WHERE T1.C1=a OR T2.C2=b", where {C1,C2} are the subset of {C1,C2,C3} with maximal joinable columns (i.e., choose the columns with the most numbers, which tables they are in can be directly joined), and a,b are values randomly sampled from the database.