Support distinct on

mindsdb_sql_parser/ast/select/select.py

@@ -1,3 +1,4 @@
+from typing import List, Union
 import json
 from mindsdb_sql_parser.ast.base import ASTNode
 from mindsdb_sql_parser.utils import indent
@@ -7,7 +8,7 @@ class Select(ASTNode):
 
     def __init__(self,
                  targets,
-                 distinct=False,
+                 distinct: Union[List, bool] = False,
                  from_table=None,
                  where=None,
                  group_by=None,
@@ -22,6 +23,8 @@ def __init__(self,
                  *args, **kwargs):
         super().__init__(*args, **kwargs)
         self.targets = targets
+
+        # if it is list: SELECT DISTINCT ON (c1, c2) ...
         self.distinct = distinct
         self.from_table = from_table
         self.where = where
@@ -105,8 +108,12 @@ def get_string(self, *args, **kwargs):
 
         out_str += "SELECT"
 
-        if self.distinct:
+        if self.distinct is True:
             out_str += ' DISTINCT'
+        elif isinstance(self.distinct, list):
+            distinct_str = ', '.join([c.to_string() for c in self.distinct])
+
+            out_str += f' DISTINCT ON ({distinct_str})'
 
         targets_str = ', '.join([out.to_string() for out in self.targets])
         out_str += f' {targets_str}'

mindsdb_sql_parser/parser.py

@@ -1300,6 +1300,11 @@ def select(self, p):
         targets = p.result_columns
         return Select(targets=targets, distinct=True)
 
+    @_('SELECT DISTINCT ON LPAREN expr_list RPAREN result_columns')
+    def select(self, p):
+        targets = p.result_columns
+        return Select(targets=targets, distinct=p.expr_list)
+
     @_('SELECT result_columns')
     def select(self, p):
         targets = p.result_columns

tests/test_base_sql/test_select_structure.py

@@ -121,6 +121,32 @@ def test_select_distinct(self):
         assert str(parse_sql(sql)) == sql
         assert parse_sql(sql).distinct
 
+    def test_select_distinct_on(self):
+        # single column with parts, star
+        sql = """SELECT DISTINCT ON (t1.column1) * FROM t1"""
+
+        expected_ast = Select(
+            targets=[Star()],
+            from_table=Identifier('t1'),
+            distinct=[Identifier('t1.column1')]
+        )
+        ast = parse_sql(sql)
+        assert str(ast) == str(expected_ast)
+        assert ast.to_tree() == expected_ast.to_tree()
+
+        # many columns without parts, not star
+
+        sql = """SELECT DISTINCT ON (column1, column2) column3, column4 FROM t1"""
+
+        expected_ast = Select(
+            targets=[Identifier('column3'), Identifier('column4')],
+            from_table=Identifier('t1'),
+            distinct=[Identifier('column1'), Identifier('column2')]
+        )
+        ast = parse_sql(sql)
+        assert str(ast) == str(expected_ast)
+        assert ast.to_tree() == expected_ast.to_tree()
+
     def test_select_multiple_from_table(self):
         sql = f'SELECT column1, column2, 1 AS renamed_constant FROM tab'
         ast = parse_sql(sql)