Support OCT() function and fix CONV() mishandling of negative floats and empty string N

sql/expression/function/conv.go

@@ -136,62 +136,66 @@ func (c *Conv) WithChildren(children ...sql.Expression) (sql.Expression, error)
 // This conversion truncates nVal as its first subpart that is convertable.
 // nVal is treated as unsigned except nVal is negative.
 func convertFromBase(ctx *sql.Context, nVal string, fromBase interface{}) interface{} {
-	fromBase, _, err := types.Int64.Convert(ctx, fromBase)
-	if err != nil {
+	if len(nVal) == 0 {
 		return nil
 	}
 
-	fromVal := int(math.Abs(float64(fromBase.(int64))))
+	// Convert and validate fromBase
+	baseVal, _, err := types.Int64.Convert(ctx, fromBase)
+	if err != nil {
+		return nil
+	}
+	fromVal := int(math.Abs(float64(baseVal.(int64))))
 	if fromVal < 2 || fromVal > 36 {
 		return nil
 	}
 
+	// Handle sign
 	negative := false
-	var upper string
-	var lower string
-	if nVal[0] == '-' {
+	switch {
+	case nVal[0] == '-':
+		if len(nVal) == 1 {
+			return uint64(0)
+		}
 		negative = true
 		nVal = nVal[1:]
-	} else if nVal[0] == '+' {
+	case nVal[0] == '+':
+		if len(nVal) == 1 {
+			return uint64(0)
+		}
 		nVal = nVal[1:]
 	}
 
-	// check for upper and lower bound for given fromBase
+	// Determine bounds based on sign
+	var maxLen int
 	if negative {
-		upper = strconv.FormatInt(math.MaxInt64, fromVal)
-		lower = strconv.FormatInt(math.MinInt64, fromVal)
-		if len(nVal) > len(lower) {
-			nVal = lower
-		} else if len(nVal) > len(upper) {
-			nVal = upper
+		maxLen = len(strconv.FormatInt(math.MinInt64, fromVal))
+		if len(nVal) > maxLen {
+			// Use MinInt64 representation in the given base
+			nVal = strconv.FormatInt(math.MinInt64, fromVal)[1:] // remove minus sign
 		}
 	} else {
-		upper = strconv.FormatUint(math.MaxUint64, fromVal)
-		lower = "0"
-		if len(nVal) < len(lower) {
-			nVal = lower
-		} else if len(nVal) > len(upper) {
-			nVal = upper
+		maxLen = len(strconv.FormatUint(math.MaxUint64, fromVal))
+		if len(nVal) > maxLen {
+			// Use MaxUint64 representation in the given base
+			nVal = strconv.FormatUint(math.MaxUint64, fromVal)
 		}
 	}
 
-	truncate := false
-	result := uint64(0)
-	i := 1
-	for !truncate && i <= len(nVal) {
+	// Find the longest valid prefix that can be converted
+	var result uint64
+	for i := 1; i <= len(nVal); i++ {
 		val, err := strconv.ParseUint(nVal[:i], fromVal, 64)
 		if err != nil {
-			truncate = true
-			return result
+			break
 		}
 		result = val
-		i++
 	}
 
 	if negative {
+		// MySQL returns signed value for negative inputs
 		return int64(result) * -1
 	}
-
 	return result
 }
 

sql/expression/function/conv_test.go

@@ -35,6 +35,8 @@ func TestConv(t *testing.T) {
 		{"n is nil", types.Int32, sql.NewRow(nil, 16, 2), nil},
 		{"fromBase is nil", types.LongText, sql.NewRow('a', nil, 2), nil},
 		{"toBase is nil", types.LongText, sql.NewRow('a', 16, nil), nil},
+		{"empty n string", types.LongText, sql.NewRow("", 3, 4), nil},
+		{"empty arg strings", types.LongText, sql.NewRow(4, "", ""), nil},
 
 		// invalid inputs
 		{"invalid N", types.LongText, sql.NewRow("r", 16, 2), "0"},

sql/expression/function/oct.go

@@ -0,0 +1,91 @@
+// Copyright 2025 Dolthub, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package function
+
+import (
+	"fmt"
+
+	"github.com/dolthub/go-mysql-server/sql"
+	"github.com/dolthub/go-mysql-server/sql/expression"
+	"github.com/dolthub/go-mysql-server/sql/types"
+)
+
+// Oct function provides a string representation for the octal value of N, where N is a decimal (base 10) number.
+type Oct struct {
+	n sql.Expression
+}
+
+var _ sql.FunctionExpression = (*Oct)(nil)
+var _ sql.CollationCoercible = (*Oct)(nil)
+
+// NewOct returns a new Oct expression.
+func NewOct(n sql.Expression) sql.Expression { return &Oct{n} }
+
+// FunctionName implements sql.FunctionExpression.
+func (o *Oct) FunctionName() string {
+	return "oct"
+}
+
+// Description implements sql.FunctionExpression.
+func (o *Oct) Description() string {
+	return "returns a string representation for octal value of N, where N is a decimal (base 10) number."
+}
+
+// Type implements the Expression interface.
+func (o *Oct) Type() sql.Type {
+	return types.LongText
+}
+
+// IsNullable implements the Expression interface.
+func (o *Oct) IsNullable() bool {
+	return o.n.IsNullable()
+}
+
+// Eval implements the Expression interface.
+func (o *Oct) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
+	// Convert a decimal (base 10) number to octal (base 8)
+	return NewConv(
+		o.n,
+		expression.NewLiteral(10, types.Int64),
+		expression.NewLiteral(8, types.Int64),
+	).Eval(ctx, row)
+}
+
+// Resolved implements the Expression interface.
+func (o *Oct) Resolved() bool {
+	return o.n.Resolved()
+}
+
+// Children implements the Expression interface.
+func (o *Oct) Children() []sql.Expression {
+	return []sql.Expression{o.n}
+}
+
+// WithChildren implements the Expression interface.
+func (o *Oct) WithChildren(children ...sql.Expression) (sql.Expression, error) {
+	if len(children) != 1 {
+		return nil, sql.ErrInvalidChildrenNumber.New(o, len(children), 1)
+	}
+	return NewOct(children[0]), nil
+}
+
+func (o *Oct) String() string {
+	return fmt.Sprintf("%s(%s)", o.FunctionName(), o.n)
+}
+
+// CollationCoercibility implements the interface sql.CollationCoercible.
+func (*Oct) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID, coercibility byte) {
+	return ctx.GetCollation(), 4 // strings with collations
+}

sql/expression/function/oct_test.go

@@ -0,0 +1,80 @@
+// Copyright 2025 Dolthub, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package function
+
+import (
+	"math"
+	"testing"
+
+	"github.com/dolthub/go-mysql-server/sql"
+	"github.com/dolthub/go-mysql-server/sql/expression"
+	"github.com/dolthub/go-mysql-server/sql/types"
+)
+
+type test struct {
+	name     string
+	nType    sql.Type
+	row      sql.Row
+	expected interface{}
+}
+
+func TestOct(t *testing.T) {
+	tests := []test{
+		// NULL input
+		{"n is nil", types.Int32, sql.NewRow(nil), nil},
+
+		// Positive numbers
+		{"positive small", types.Int32, sql.NewRow(8), "10"},
+		{"positive medium", types.Int32, sql.NewRow(64), "100"},
+		{"positive large", types.Int32, sql.NewRow(4095), "7777"},
+		{"positive huge", types.Int64, sql.NewRow(123456789), "726746425"},
+
+		// Negative numbers
+		{"negative small", types.Int32, sql.NewRow(-8), "1777777777777777777770"},
+		{"negative medium", types.Int32, sql.NewRow(-64), "1777777777777777777700"},
+		{"negative large", types.Int32, sql.NewRow(-4095), "1777777777777777770001"},
+
+		// Zero
+		{"zero", types.Int32, sql.NewRow(0), "0"},
+
+		// String inputs
+		{"string number", types.LongText, sql.NewRow("15"), "17"},
+		{"alpha string", types.LongText, sql.NewRow("abc"), "0"},
+		{"mixed string", types.LongText, sql.NewRow("123abc"), "173"},
+
+		// Edge cases
+		{"max int32", types.Int32, sql.NewRow(math.MaxInt32), "17777777777"},
+		{"min int32", types.Int32, sql.NewRow(math.MinInt32), "1777777777760000000000"},
+		{"max int64", types.Int64, sql.NewRow(math.MaxInt64), "777777777777777777777"},
+		{"min int64", types.Int64, sql.NewRow(math.MinInt64), "1000000000000000000000"},
+
+		// Decimal numbers
+		{"decimal", types.Float64, sql.NewRow(15.5), "17"},
+		{"negative decimal", types.Float64, sql.NewRow(-15.5), "1777777777777777777761"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			f := NewOct(expression.NewGetField(0, tt.nType, "n", true))
+			result, err := f.Eval(sql.NewEmptyContext(), tt.row)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if result != tt.expected {
+				t.Errorf("got %v; expected %v", result, tt.expected)
+			}
+		})
+	}
+}

sql/expression/function/registry.go

@@ -184,6 +184,7 @@ var BuiltIns = []sql.Function{
 	sql.Function1{Name: "ntile", Fn: window.NewNTile},
 	sql.FunctionN{Name: "now", Fn: NewNow},
 	sql.Function2{Name: "nullif", Fn: NewNullIf},
+	sql.Function1{Name: "oct", Fn: NewOct},
 	sql.Function1{Name: "octet_length", Fn: NewLength},
 	sql.Function1{Name: "ord", Fn: NewOrd},
 	sql.Function0{Name: "pi", Fn: NewPi},