Go back to helper function

src/dialect/mod.rs

@@ -562,7 +562,13 @@ pub trait Dialect: Debug + Any {
         false
     }
 
-    /// For example: SELECT col_alias = col FROM tbl
+    /// Returns true if this dialect supports treating the equals operator `=` within a [`SelectItem`]
+    /// as an alias assignment operator, rather than a boolean expression.
+    /// For example: the following statements are equivalent for such a dialect:
+    /// ```sql
+    ///  SELECT col_alias = col FROM tbl;
+    ///  SELECT col_alias AS col FROM tbl;
+    /// ```
     fn supports_eq_alias_assigment(&self) -> bool {
         false
     }

src/parser/mod.rs

@@ -11174,29 +11174,11 @@ impl<'a> Parser<'a> {
                 )
             }
             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
-                // [MsSql]: 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
-                let expr = if self.dialect.supports_eq_alias_assigment() {
-                    if let Expr::BinaryOp {
-                        ref left,
-                        op: BinaryOperator::Eq,
-                        ref right,
-                    } = expr
-                    {
-                        if let Expr::Identifier(alias) = left.as_ref() {
-                            return Ok(SelectItem::ExprWithAlias {
-                                expr: *right.clone(),
-                                alias: alias.clone(),
-                            });
-                        }
+                if self.dialect.supports_eq_alias_assigment() {
+                    if let Some(select_item) = Self::maybe_unpack_alias_assignment(&expr) {
+                        return Ok(select_item);
                     }
-                    expr
-                } else {
-                    expr
-                };
-
-                // Parse the common AS keyword for aliasing a column
+                }
                 self.parse_optional_alias(keywords::RESERVED_FOR_COLUMN_ALIAS)
                     .map(|alias| match alias {
                         Some(alias) => SelectItem::ExprWithAlias { expr, alias },
@@ -12212,6 +12194,28 @@ impl<'a> Parser<'a> {
         }
         false
     }
+
+    /// 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
+    /// [MsSql]: <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 maybe_unpack_alias_assignment(expr: &Expr) -> Option<SelectItem> {
+        if let Expr::BinaryOp {
+            left,
+            op: BinaryOperator::Eq,
+            right,
+            ..
+        } = expr
+        {
+            if let Expr::Identifier(ref alias) = **left {
+                return Some(SelectItem::ExprWithAlias {
+                    expr: *right.clone(),
+                    alias: alias.clone(),
+                });
+            }
+        }
+
+        None
+    }
 }
 
 impl Word {

tests/sqlparser_common.rs

@@ -11408,3 +11408,15 @@ fn test_any_some_all_comparison() {
     verified_stmt("SELECT c1 FROM tbl WHERE c1 <> SOME(SELECT c2 FROM tbl)");
     verified_stmt("SELECT 1 = ANY(WITH x AS (SELECT 1) SELECT * FROM x)");
 }
+
+#[test]
+fn test_alias_equal_expr() {
+    let dialects = all_dialects_where(|d| d.supports_eq_alias_assigment());
+    let sql = r#"SELECT some_alias = some_column FROM some_table"#;
+    let expected = r#"SELECT some_column AS some_alias FROM some_table"#;
+    let _ = dialects.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 _ = dialects.one_statement_parses_to(sql, expected);
+}

tests/sqlparser_mssql.rs

@@ -1024,17 +1024,6 @@ 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 {})],