expression: fix the return type of coalesce when arg type is DATE (#5…

…5969)

close #46475

expression/builtin_compare.go

@@ -118,18 +118,19 @@ func (c *coalesceFunctionClass) getFunction(ctx sessionctx.Context, args []Expre
 		return nil, err
 	}
 
-	fieldTps := make([]*types.FieldType, 0, len(args))
+	flag := uint(0)
 	for _, arg := range args {
-		fieldTps = append(fieldTps, arg.GetType())
+		flag |= arg.GetType().GetFlag() & mysql.NotNullFlag
 	}
 
-	// Use the aggregated field type as retType.
-	resultFieldType := types.AggFieldType(fieldTps)
-	var tempType uint
-	resultEvalType := types.AggregateEvalType(fieldTps, &tempType)
-	resultFieldType.SetFlag(tempType)
-	retEvalTp := resultFieldType.EvalType()
+	resultFieldType, err := InferType4ControlFuncs(ctx, c.funcName, args...)
+	if err != nil {
+		return nil, err
+	}
+
+	resultFieldType.AddFlag(flag)
 
+	retEvalTp := resultFieldType.EvalType()
 	fieldEvalTps := make([]types.EvalType, 0, len(args))
 	for range args {
 		fieldEvalTps = append(fieldEvalTps, retEvalTp)
@@ -140,60 +141,7 @@ func (c *coalesceFunctionClass) getFunction(ctx sessionctx.Context, args []Expre
 		return nil, err
 	}
 
-	bf.tp.AddFlag(resultFieldType.GetFlag())
-	resultFieldType.SetFlen(0)
-	resultFieldType.SetDecimal(types.UnspecifiedLength)
-
-	// Set retType to BINARY(0) if all arguments are of type NULL.
-	if resultFieldType.GetType() == mysql.TypeNull {
-		types.SetBinChsClnFlag(bf.tp)
-		resultFieldType.SetFlen(0)
-		resultFieldType.SetDecimal(0)
-	} else {
-		maxIntLen := 0
-		maxFlen := 0
-
-		// Find the max length of field in `maxFlen`,
-		// and max integer-part length in `maxIntLen`.
-		for _, argTp := range fieldTps {
-			if argTp.GetDecimal() > resultFieldType.GetDecimal() {
-				resultFieldType.SetDecimalUnderLimit(argTp.GetDecimal())
-			}
-			argIntLen := argTp.GetFlen()
-			if argTp.GetDecimal() > 0 {
-				argIntLen -= argTp.GetDecimal() + 1
-			}
-
-			// Reduce the sign bit if it is a signed integer/decimal
-			if !mysql.HasUnsignedFlag(argTp.GetFlag()) {
-				argIntLen--
-			}
-			if argIntLen > maxIntLen {
-				maxIntLen = argIntLen
-			}
-			if argTp.GetFlen() > maxFlen || argTp.GetFlen() == types.UnspecifiedLength {
-				maxFlen = argTp.GetFlen()
-			}
-		}
-		// For integer, field length = maxIntLen + (1/0 for sign bit)
-		// For decimal, field length = maxIntLen + maxDecimal + (1/0 for sign bit)
-		if resultEvalType == types.ETInt || resultEvalType == types.ETDecimal {
-			resultFieldType.SetFlenUnderLimit(maxIntLen + resultFieldType.GetDecimal())
-			if resultFieldType.GetDecimal() > 0 {
-				resultFieldType.SetFlenUnderLimit(resultFieldType.GetFlen() + 1)
-			}
-			if !mysql.HasUnsignedFlag(resultFieldType.GetFlag()) {
-				resultFieldType.SetFlenUnderLimit(resultFieldType.GetFlen() + 1)
-			}
-			bf.tp = resultFieldType
-		} else {
-			bf.tp.SetFlen(maxFlen)
-		}
-		// Set the field length to maxFlen for other types.
-		if bf.tp.GetFlen() > mysql.MaxDecimalWidth {
-			bf.tp.SetFlen(mysql.MaxDecimalWidth)
-		}
-	}
+	bf.tp = resultFieldType
 
 	switch retEvalTp {
 	case types.ETInt:

expression/builtin_compare_test.go

@@ -406,3 +406,12 @@ func TestGreatestLeastFunc(t *testing.T) {
 	_, err = funcs[ast.Least].getFunction(ctx, []Expression{NewZero(), NewOne()})
 	require.NoError(t, err)
 }
+
+func TestIssue46475(t *testing.T) {
+	ctx := createContext(t)
+	args := []interface{}{nil, dt, nil}
+
+	f, err := newFunctionForTest(ctx, ast.Coalesce, primitiveValsToConstants(ctx, args)...)
+	require.NoError(t, err)
+	require.Equal(t, f.GetType().GetType(), mysql.TypeDate)
+}