planner: Do not pushdown unsupported function to tiflash in TopN oper…

…ator (pingcap#19363)

Co-authored-by: ti-srebot <66930949+ti-srebot@users.noreply.github.com>

planner/core/task.go

@@ -813,11 +813,7 @@ func (p *PhysicalTopN) canPushDown(cop *copTask) bool {
 	for _, item := range p.ByItems {
 		exprs = append(exprs, item.Expr)
 	}
-	storeType := kv.TiKV
-	if tableScan, ok := cop.tablePlan.(*PhysicalTableScan); ok {
-		storeType = tableScan.StoreType
-	}
-	return expression.CanExprsPushDown(p.ctx.GetSessionVars().StmtCtx, exprs, p.ctx.GetClient(), storeType)
+	return expression.CanExprsPushDown(p.ctx.GetSessionVars().StmtCtx, exprs, p.ctx.GetClient(), cop.getStoreType())
 }
 
 func (p *PhysicalTopN) allColsFromSchema(schema *expression.Schema) bool {

planner/core/testdata/integration_serial_suite_in.json

@@ -3,7 +3,9 @@
     "name": "TestSelPushDownTiFlash",
     "cases": [
       "explain select * from t where t.a > 1 and t.b = \"flash\" or t.a + 3 * t.a = 5",
-      "explain select * from t where cast(t.a as float) + 3 = 5.1"
+      "explain select * from t where cast(t.a as float) + 3 = 5.1",
+      "explain select * from t where b > 'a' order by convert(b, unsigned) limit 2",
+      "explain select * from t where b > 'a' order by b limit 2"
     ]
   },
   {

planner/core/testdata/integration_serial_suite_out.json

@@ -17,6 +17,27 @@
           "└─TableReader_6 10000.00 root  data:TableFullScan_5",
           "  └─TableFullScan_5 10000.00 cop[tiflash] table:t keep order:false, stats:pseudo"
         ]
+      },
+      {
+        "SQL": "explain select * from t where b > 'a' order by convert(b, unsigned) limit 2",
+        "Plan": [
+          "Projection_17 2.00 root  test.t.a, test.t.b",
+          "└─TopN_8 2.00 root  Column#3, offset:0, count:2",
+          "  └─Projection_18 3333.33 root  test.t.a, test.t.b, cast(test.t.b, bigint(22) UNSIGNED BINARY)->Column#3",
+          "    └─TableReader_13 3333.33 root  data:Selection_12",
+	  "      └─Selection_12 3333.33 cop[tiflash]  gt(test.t.b, \"a\")",
+	  "        └─TableFullScan_11 10000.00 cop[tiflash] table:t keep order:false, stats:pseudo"
+        ]
+      },
+      {
+        "SQL": "explain select * from t where b > 'a' order by b limit 2",
+        "Plan": [
+          "TopN_8 2.00 root  test.t.b, offset:0, count:2",
+          "└─TableReader_17 2.00 root  data:TopN_16",
+          "  └─TopN_16 2.00 cop[tiflash]  test.t.b, offset:0, count:2",
+	  "    └─Selection_15 3333.33 cop[tiflash]  gt(test.t.b, \"a\")",
+          "      └─TableFullScan_14 10000.00 cop[tiflash] table:t keep order:false, stats:pseudo"
+        ]
       }
     ]
   },