planner: fix cte-schema-clone will clone the old hashcode of its colu…

…mn if any (#35415) (#35495)

close #35404

cmd/explaintest/r/explain_cte.result

@@ -479,3 +479,22 @@ CTE_1	8000.00	root		Non-Recursive CTE
 CTE_0	10000.00	root		Non-Recursive CTE
 └─TableReader(Seed Part)	10000.00	root		data:TableFullScan
   └─TableFullScan	10000.00	cop[tikv]	table:t1	keep order:false, stats:pseudo
+drop table if exists tbl;
+create table tbl (id int);
+explain with t1 as (select id from tbl), t2 as (select a.id from t1 a join t1 b on a.id = b.id) select * from t2 where id in (select id from t2);
+id	estRows	task	access object	operator info
+HashJoin_33	8000.00	root		inner join, equal:[eq(test.tbl.id, test.tbl.id)]
+├─HashAgg_37(Build)	5120.00	root		group by:test.tbl.id, funcs:firstrow(test.tbl.id)->test.tbl.id
+│ └─Selection_38	8000.00	root		not(isnull(test.tbl.id))
+│   └─CTEFullScan_39	10000.00	root	CTE:t2	data:CTE_1
+└─Selection_35(Probe)	8000.00	root		not(isnull(test.tbl.id))
+  └─CTEFullScan_36	10000.00	root	CTE:t2	data:CTE_1
+CTE_1	10000.00	root		Non-Recursive CTE
+└─HashJoin_25(Seed Part)	10000.00	root		inner join, equal:[eq(test.tbl.id, test.tbl.id)]
+  ├─Selection_29(Build)	8000.00	root		not(isnull(test.tbl.id))
+  │ └─CTEFullScan_30	10000.00	root	CTE:b	data:CTE_0
+  └─Selection_27(Probe)	8000.00	root		not(isnull(test.tbl.id))
+    └─CTEFullScan_28	10000.00	root	CTE:a	data:CTE_0
+CTE_0	10000.00	root		Non-Recursive CTE
+└─TableReader_22(Seed Part)	10000.00	root		data:TableFullScan_21
+  └─TableFullScan_21	10000.00	cop[tikv]	table:tbl	keep order:false, stats:pseudo

cmd/explaintest/t/explain_cte.test

@@ -258,3 +258,8 @@ desc format='brief' with all_data as
 select v1.tps v1_tps,v2.tps v2_tps
 from version1 v1, version2 v2
 where v1.bench_type =v2.bench_type;
+
+# issue 35404
+drop table if exists tbl;
+create table tbl (id int);
+explain with t1 as (select id from tbl), t2 as (select a.id from t1 a join t1 b on a.id = b.id) select * from t2 where id in (select id from t2);

expression/column.go

@@ -490,6 +490,11 @@ func (col *Column) HashCode(_ *stmtctx.StatementContext) []byte {
 	return col.hashcode
 }
 
+// CleanHashCode will clean the hashcode you may be cached before. It's used especially in schema-cloned & reallocated-uniqueID's cases.
+func (col *Column) CleanHashCode() {
+	col.hashcode = make([]byte, 0, 9)
+}
+
 // ResolveIndices implements Expression interface.
 func (col *Column) ResolveIndices(schema *Schema) (Expression, error) {
 	newCol := col.Clone()

planner/core/logical_plan_builder.go

@@ -6889,6 +6889,8 @@ func getResultCTESchema(seedSchema *expression.Schema, svar *variable.SessionVar
 		col.RetType = col.RetType.Clone()
 		col.UniqueID = svar.AllocPlanColumnID()
 		col.RetType.DelFlag(mysql.NotNullFlag)
+		// Since you have reallocated unique id here, the old-cloned-cached hash code is not valid anymore.
+		col.CleanHashCode()
 	}
 	return res
 }