my cluster is cdh5.14  impala 2.11 kudu 1.6.0 impala on kudu,When union all is used to merge more than three select join queries, the third and later select must perform full table scanning. How can I solve the problem of full table scanning? A full table scan is not performed when the select join statement is executed alone. sql as follows: SELECT mb.unitno, mb.materialcode, mb.starttime, mb.length, ib.equipmentcode, ib.defectclass, ib.defectname, ib.side FROM sc1.tba1 mb LEFT OUTER JOIN sc1.tbb1 ib ON mb.materialcode = ib.materialcode where mb.starttime>'20240827'and mb.starttime<'20240828' ) UNION ALL SELECT md.unitno, md.materialcode, md.starttime, md.length, id.equipmentcode, id.defectclass, id.defectname, id.side FROM sc1.tba2 md LEFT OUTER JOIN sc1.tbb2 id ON md.materialcode = id.materialcode where md.starttime>'20240827'and md.starttime<'20240828' ) UNION ALL SELECT me.unitno, me.materialcode, me.starttime, me.length, ie.equipmentcode, ie.defectclass, ie.defectname, ie.side FROM sc1.tba3 me LEFT OUTER JOIN sc1.tbb3 ie ON me.materialcode = ie.materialcode where me.starttime>'20240827'and me.starttime<'20240828' )； The number of tbb1, tbb2, and tbb3 rows is 800 million，The number of tba1, tba2, and tbba3 rows is 10000. When executing the above sql, a full table scan is performed on sc1.tbb3.   ... View more