Support multiple SET variables (#1252)

src/dialect/mod.rs

@@ -217,6 +217,15 @@ pub trait Dialect: Debug + Any {
     fn supports_lambda_functions(&self) -> bool {
         false
     }
+    /// Returns true if the dialect supports multiple variable assignment
+    /// using parentheses in a `SET` variable declaration.
+    ///
+    /// ```sql
+    /// SET (variable[, ...]) = (expression[, ...]);
+    /// ```
+    fn supports_parenthesized_set_variables(&self) -> bool {
+        false
+    }
     /// Returns true if the dialect has a CONVERT function which accepts a type first
     /// and an expression second, e.g. `CONVERT(varchar, 1)`
     fn convert_type_before_value(&self) -> bool {