properly convert enum/set columns to string columns with alter table

Author: angelamayxie

memory/table.go

@@ -1413,7 +1413,8 @@ func (t *Table) ModifyColumn(ctx *sql.Context, columnName string, column *sql.Co
 			var oldRowWithoutVal sql.Row
 			oldRowWithoutVal = append(oldRowWithoutVal, row[:oldIdx]...)
 			oldRowWithoutVal = append(oldRowWithoutVal, row[oldIdx+1:]...)
-			newVal, inRange, err := column.Type.Convert(ctx, row[oldIdx])
+			oldType := data.schema.Schema[oldIdx].Type
+			newVal, inRange, err := types.TypeAwareConversion(ctx, row[oldIdx], oldType, column.Type)
 			if err != nil {
 				if sql.ErrNotMatchingSRID.Is(err) {
 					err = sql.ErrNotMatchingSRIDWithColName.New(columnName, err)

sql/expression/case.go

@@ -136,7 +136,7 @@ func (c *Case) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
 			}
 			// When unable to convert to the type of the case, return the original value
 			// A common error here is "Out of bounds value for decimal type"
-			if ret, err := types.TypeAwareConversion(ctx, bval, b.Value.Type(), t); err == nil {
+			if ret, inRange, err := types.TypeAwareConversion(ctx, bval, b.Value.Type(), t); inRange && err == nil {
 				return ret, nil
 			}
 			return bval, nil
@@ -150,7 +150,7 @@ func (c *Case) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
 		}
 		// When unable to convert to the type of the case, return the original value
 		// A common error here is "Out of bounds value for decimal type"
-		if ret, err := types.TypeAwareConversion(ctx, val, c.Else.Type(), t); err == nil {
+		if ret, inRange, err := types.TypeAwareConversion(ctx, val, c.Else.Type(), t); inRange && err == nil {
 			return ret, nil
 		}
 		return val, nil

sql/expression/comparison.go

@@ -188,7 +188,7 @@ func (c *comparison) castLeftAndRight(ctx *sql.Context, left, right interface{})
 			if r, inRange, err := leftType.Convert(ctx, right); inRange && err == nil {
 				return left, r, leftType, nil
 			} else {
-				l, err := types.TypeAwareConversion(ctx, left, leftType, rightType)
+				l, _, err := types.TypeAwareConversion(ctx, left, leftType, rightType)
 				if err != nil {
 					return nil, nil, nil, err
 				}
@@ -200,7 +200,7 @@ func (c *comparison) castLeftAndRight(ctx *sql.Context, left, right interface{})
 			if l, inRange, err := rightType.Convert(ctx, left); inRange && err == nil {
 				return l, right, rightType, nil
 			} else {
-				r, err := types.TypeAwareConversion(ctx, right, rightType, leftType)
+				r, _, err := types.TypeAwareConversion(ctx, right, rightType, leftType)
 				if err != nil {
 					return nil, nil, nil, err
 				}

sql/expression/convert.go

@@ -291,10 +291,7 @@ func convertValue(ctx *sql.Context, val interface{}, castTo string, originType s
 	}
 	switch strings.ToLower(castTo) {
 	case ConvertToBinary:
-		if types.IsSet(originType) || types.IsEnum(originType) {
-			val, _ = types.TypeAwareConversion(ctx, val, originType, types.LongText)
-		}
-		b, _, err := types.LongBlob.Convert(ctx, val)
+		b, _, err := types.TypeAwareConversion(ctx, val, originType, types.LongBlob)
 		if err != nil {
 			return nil, nil
 		}
@@ -312,7 +309,7 @@ func convertValue(ctx *sql.Context, val interface{}, castTo string, originType s
 		}
 		return truncateConvertedValue(b, typeLength)
 	case ConvertToChar, ConvertToNChar:
-		s, err := types.TypeAwareConversion(ctx, val, originType, types.LongText)
+		s, _, err := types.TypeAwareConversion(ctx, val, originType, types.LongText)
 		if err != nil {
 			return nil, nil
 		}

sql/types/conversion.go

@@ -738,19 +738,16 @@ func GeneralizeTypes(a, b sql.Type) sql.Type {
 // TypeAwareConversion converts a value to a specified type, with awareness of the value's original type. This is
 // necessary because some types, such as EnumType and SetType, are stored as ints and require information from the
 // original type to properly convert to strings.
-func TypeAwareConversion(ctx *sql.Context, val interface{}, originalType sql.Type, convertedType sql.Type) (interface{}, error) {
+func TypeAwareConversion(ctx *sql.Context, val interface{}, originalType sql.Type, convertedType sql.Type) (interface{}, sql.ConvertInRange, error) {
 	if val == nil {
-		return nil, nil
+		return nil, sql.InRange, nil
 	}
-	var converted interface{}
 	var err error
-	if IsTextOnly(convertedType) {
-		converted, _, err = ConvertToCollatedString(ctx, val, originalType)
-	} else {
-		converted, _, err = convertedType.Convert(ctx, val)
-	}
-	if err != nil {
-		return nil, err
+	if (IsEnum(originalType) || IsSet(originalType)) && IsText(convertedType) {
+		val, _, err = ConvertToCollatedString(ctx, val, originalType)
+		if err != nil {
+			return nil, sql.OutOfRange, err
+		}
 	}
-	return converted, nil
+	return convertedType.Convert(ctx, val)
 }