This is an automated cherry-pick of pingcap#52542

Signed-off-by: ti-chi-bot <[email protected]>

cmd/explaintest/r/explain_easy.result

@@ -523,7 +523,11 @@ StreamAgg	1.00	root		funcs:count(1)->Column#22
       │   └─Projection	1.00	root		Column#33, Column#34, Column#35, Column#14, Column#15, Column#16
       │     └─HashAgg	1.00	root		group by:test.test01.region_id, test.test01.show_date, test.test01.stat_date, funcs:firstrow(test.test01.stat_date)->Column#33, funcs:firstrow(test.test01.show_date)->Column#34, funcs:firstrow(test.test01.region_id)->Column#35, funcs:firstrow(test.test01.stat_date)->Column#14, funcs:firstrow(test.test01.show_date)->Column#15, funcs:firstrow(test.test01.region_id)->Column#16, funcs:count(1)->Column#39
       │       └─TableReader	0.01	root		data:Selection
+<<<<<<< HEAD:cmd/explaintest/r/explain_easy.result
       │         └─Selection	0.01	cop[tikv]		eq(test.test01.period, 1), ge(test.test01.stat_date, 20191202), gt(cast(test.test01.registration_num, bigint(20) BINARY), 0), le(test.test01.stat_date, 20191202)
+=======
+      │         └─Selection	0.01	cop[tikv]		eq(explain_easy.test01.period, 1), ge(explain_easy.test01.stat_date, 20191202), gt(cast(explain_easy.test01.registration_num, decimal(20,0) BINARY), 0), le(explain_easy.test01.stat_date, 20191202)
+>>>>>>> 09c8f964cc5 (planner: fix the issue that UnionAll didn't handle the range bump case (#52542)):tests/integrationtest/r/explain_easy.result
       │           └─TableFullScan	10000.00	cop[tikv]	table:test01	keep order:false, stats:pseudo
       └─TableReader(Probe)	2.00	root		data:TableRangeScan
         └─TableRangeScan	2.00	cop[tikv]	table:b	range: decided by [Column#16], keep order:false, stats:pseudo

planner/core/logical_plan_builder.go

@@ -1692,7 +1692,7 @@ func unionJoinFieldType(a, b *types.FieldType) *types.FieldType {
 	} else if b.GetType() == mysql.TypeNull {
 		return a
 	}
-	resultTp := types.NewFieldType(types.MergeFieldType(a.GetType(), b.GetType()))
+	resultTp := types.AggFieldType([]*types.FieldType{a, b})
 	// This logic will be intelligible when it is associated with the buildProjection4Union logic.
 	if resultTp.GetType() == mysql.TypeNewDecimal {
 		// The decimal result type will be unsigned only when all the decimals to be united are unsigned.

types/field_type.go

@@ -68,7 +68,7 @@ func AggFieldType(tps []*FieldType) *FieldType {
 			currType = *t
 			continue
 		}
-		mtp := MergeFieldType(currType.GetType(), t.GetType())
+		mtp := mergeFieldType(currType.GetType(), t.GetType())
 		isMixedSign = isMixedSign || (mysql.HasUnsignedFlag(currType.GetFlag()) != mysql.HasUnsignedFlag(t.GetFlag()))
 		currType.SetType(mtp)
 		currType.SetFlag(mergeTypeFlag(currType.GetFlag(), t.GetFlag()))
@@ -353,12 +353,16 @@ func DefaultCharsetForType(tp byte) (defaultCharset string, defaultCollation str
 	return charset.CharsetBin, charset.CollationBin
 }
 
-// MergeFieldType merges two MySQL type to a new type.
+// mergeFieldType merges two MySQL type to a new type.
 // This is used in hybrid field type expression.
 // For example "select case c when 1 then 2 when 2 then 'tidb' from t;"
 // The result field type of the case expression is the merged type of the two when clause.
 // See https://github.com/mysql/mysql-server/blob/8.0/sql/field.cc#L1042
-func MergeFieldType(a byte, b byte) byte {
+//
+// This function doesn't handle the range bump: for example, when the unsigned long is merged with signed long,
+// the result should be longlong. However, this function returns long for this case. Please use `AggFieldType`
+// function if you need to handle the range bump.
+func mergeFieldType(a byte, b byte) byte {
 	ia := getFieldTypeIndex(a)
 	ib := getFieldTypeIndex(b)
 	return fieldTypeMergeRules[ia][ib]