fix: Add MySQL-specific operators (div, mod) to IsMathematicalOperator

The MySQL parser uses symbolic names like 'div' and 'mod' instead of '/' and '%'.
Added these to operator.go with TODO comments indicating they should be moved to
engine-specific logic during refactoring.

This fixes the division case in type inference where (a1 / 1024) was generating
interface{} instead of the correct decimal/string type.

All 3 test cases now work correctly:
- ListTest: Simple division generates string/sql.NullString
- ListTest4: Arithmetic with nullability generates sql.NullInt32
- ListTest5: COALESCE generates string

Author: rubensantoniorosa2704

examples/type-inference-test/mysql/db.go

@@ -142,24 +142,18 @@ func combineMySQLTypes(left, right *Column, operator string, notNull bool) *Colu
 		return left
 	}
 
-	// Normalize MySQL-specific operators
 	switch operator {
-	case "div":
-		operator = "/" // DIV is MySQL's integer division, but for type inference treat as division
-	case "mod":
-		operator = "%" // MOD is alias for %
-	}
-
-	switch operator {
-	case "/":
+	case "/", "div":
 		// Division: int/int = decimal, float/anything = float
+		// Note: "div" is MySQL-specific operator recognized by IsMathematicalOperator()
 		if isFloatType(left.DataType) || isFloatType(right.DataType) {
 			return &Column{DataType: "float", NotNull: notNull}
 		}
 		return &Column{DataType: "decimal", NotNull: notNull}
 
-	case "%":
+	case "%", "mod":
 		// Modulo: returns integer if both are integers, otherwise decimal
+		// Note: "mod" is MySQL-specific operator recognized by IsMathematicalOperator()
 		if isIntegerType(left.DataType) && isIntegerType(right.DataType) {
 			return &Column{DataType: "int", NotNull: notNull}
 		}

examples/type-inference-test/mysql/models.go

@@ -23,6 +23,8 @@ func IsMathematicalOperator(s string) bool {
 	case "-":
 	case "*":
 	case "/":
+	case "div": // TODO: MySQL-specific operator - should be moved to engine-specific logic
+	case "mod": // TODO: MySQL-specific operator - should be moved to engine-specific logic
 	case "%":
 	case "^":
 	case "|/":