Fix for negative len

Author: zachmu

enginetest/queries/queries.go

@@ -5453,7 +5453,13 @@ SELECT * FROM cte WHERE  d = 2;`,
 	{
 		Query: `SELECT INSERT("hello", 1, -1, "xyz")`,
 		Expected: []sql.Row{
-			{string("hello")},
+			{string("xyz")},
+		},
+	},
+	{
+		Query: `SELECT INSERT("hello", 3, -1, "xyz")`,
+		Expected: []sql.Row{
+			{string("hexyz")},
 		},
 	},
 	{

sql/expression/function/insert.go

@@ -148,8 +148,8 @@ func (i *Insert) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
 	n := newStrVal.(string)
 
 	// MySQL uses 1-based indexing for position
-	// Handle negative position or negative length
-	if p < 1 || l < 0 {
+	// Handle negative position - return original string
+	if p < 1 {
 		return s, nil
 	}
 
@@ -162,9 +162,15 @@ func (i *Insert) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
 	}
 
 	// Calculate end index
-	endIdx := startIdx + l
-	if endIdx > int64(len(s)) {
+	// For negative length, replace from position to end of string
+	var endIdx int64
+	if l < 0 {
 		endIdx = int64(len(s))
+	} else {
+		endIdx = startIdx + l
+		if endIdx > int64(len(s)) {
+			endIdx = int64(len(s))
+		}
 	}
 
 	// Build the result string

sql/expression/function/insert_test.go

@@ -45,7 +45,7 @@ func TestInsert(t *testing.T) {
 		{"empty string", sql.NewRow("", 1, 2, "new"), "", false},
 		{"position is 0", sql.NewRow("hello", 0, 2, "new"), "hello", false},
 		{"position is negative", sql.NewRow("hello", -1, 2, "new"), "hello", false},
-		{"negative length", sql.NewRow("hello", 1, -1, "new"), "hello", false},
+		{"negative length", sql.NewRow("hello", 1, -1, "new"), "new", false},
 		{"position beyond string length", sql.NewRow("hello", 10, 2, "new"), "hello", false},
 		{"normal insertion", sql.NewRow("hello", 2, 2, "xyz"), "hxyzlo", false},
 		{"insert at beginning", sql.NewRow("hello", 1, 2, "xyz"), "xyzllo", false},
@@ -54,6 +54,8 @@ func TestInsert(t *testing.T) {
 		{"length exceeds string", sql.NewRow("hello", 3, 10, "world"), "heworld", false},
 		{"empty replacement", sql.NewRow("hello", 2, 2, ""), "hlo", false},
 		{"zero length", sql.NewRow("hello", 3, 0, "xyz"), "hexyzllo", false},
+		{"negative length from middle", sql.NewRow("hello", 3, -1, "xyz"), "hexyz", false},
+		{"negative length from beginning", sql.NewRow("hello", 1, -5, "xyz"), "xyz", false},
 	}
 
 	for _, tt := range testCases {