core: Change always falseness of equivalence between variables expressions to be only on anonymous variables

Named variables are compared by name

core/util.rs

@@ -401,7 +401,9 @@ pub fn exprs_are_equivalent(expr1: &Expr, expr2: &Expr) -> bool {
         }
         // Variables that are not bound to a specific value, are treated as NULL
         // https://sqlite.org/lang_expr.html#varparam
-        (Expr::Variable(..), Expr::Variable(..)) => false,
+        (Expr::Variable(var), Expr::Variable(var2)) if var == "" && var2 == "" => false,
+        // Named variables can be compared by their name
+        (Expr::Variable(val), Expr::Variable(val2)) => val == val2,
         (Expr::Parenthesized(exprs1), Expr::Parenthesized(exprs2)) => {
             exprs1.len() == exprs2.len()
                 && exprs1
@@ -948,9 +950,20 @@ pub mod tests {
     }
 
     #[test]
-    fn test_variable_comparison() {
-        let expr1 = Expr::Variable("?".to_string());
-        let expr2 = Expr::Variable("?".to_string());
+    fn test_anonymous_variable_comparison() {
+        let expr1 = Expr::Variable("".to_string());
+        let expr2 = Expr::Variable("".to_string());
+        assert!(!exprs_are_equivalent(&expr1, &expr2));
+    }
+
+    #[test]
+    fn test_named_variable_comparison() {
+        let expr1 = Expr::Variable("1".to_string());
+        let expr2 = Expr::Variable("1".to_string());
+        assert!(exprs_are_equivalent(&expr1, &expr2));
+
+        let expr1 = Expr::Variable("1".to_string());
+        let expr2 = Expr::Variable("2".to_string());
         assert!(!exprs_are_equivalent(&expr1, &expr2));
     }