Add support for parsing MsSql alias with equals

Author: yoavcloud

src/parser/mod.rs

@@ -11173,15 +11173,42 @@ impl<'a> Parser<'a> {
                     self.peek_token().location
                 )
             }
-            expr => self
-                .parse_optional_alias(keywords::RESERVED_FOR_COLUMN_ALIAS)
-                .map(|alias| match alias {
-                    Some(alias) => SelectItem::ExprWithAlias { expr, alias },
-                    None => SelectItem::UnnamedExpr(expr),
-                }),
+            expr => {
+                if dialect_of!(self is MsSqlDialect) {
+                    if let Some(select_item) = self.parse_mssql_alias_with_equal(&expr) {
+                        return Ok(select_item);
+                    }
+                }
+                self.parse_optional_alias(keywords::RESERVED_FOR_COLUMN_ALIAS)
+                    .map(|alias| match alias {
+                        Some(alias) => SelectItem::ExprWithAlias { expr, alias },
+                        None => SelectItem::UnnamedExpr(expr),
+                    })
+            }
         }
     }
 
+    /// Parse a [`SelectItem`] based on an MsSql syntax that uses the equal sign
+    /// to denote an alias, for example: SELECT col_alias = col FROM tbl
+    /// <https://learn.microsoft.com/en-us/sql/t-sql/queries/select-examples-transact-sql?view=sql-server-ver16#b-use-select-with-column-headings-and-calculations>    
+    fn parse_mssql_alias_with_equal(&mut self, expr: &Expr) -> Option<SelectItem> {
+        if let Expr::BinaryOp {
+            left, op, right, ..
+        } = expr
+        {
+            if op == &BinaryOperator::Eq {
+                if let Expr::Identifier(ref alias) = **left {
+                    return Some(SelectItem::ExprWithAlias {
+                        expr: *right.clone(),
+                        alias: alias.clone(),
+                    });
+                }
+            }
+        }
+
+        None
+    }
+
     /// Parse an [`WildcardAdditionalOptions`] information for wildcard select items.
     ///
     /// If it is not possible to parse it, will return an option.

tests/sqlparser_mssql.rs

@@ -1024,6 +1024,17 @@ fn parse_create_table_with_identity_column() {
     }
 }
 
+#[test]
+fn test_alias_equal_expr() {
+    let sql = r#"SELECT some_alias = some_column FROM some_table"#;
+    let expected = r#"SELECT some_column AS some_alias FROM some_table"#;
+    let _ = ms().one_statement_parses_to(sql, expected);
+
+    let sql = r#"SELECT some_alias = (a*b) FROM some_table"#;
+    let expected = r#"SELECT (a * b) AS some_alias FROM some_table"#;
+    let _ = ms().one_statement_parses_to(sql, expected);
+}
+
 fn ms() -> TestedDialects {
     TestedDialects {
         dialects: vec![Box::new(MsSqlDialect {})],