Add support for LIMIT BY clause

clickhouse_sqlalchemy/drivers/base.py

@@ -100,6 +100,21 @@ def visit_if__func(self, func, **kw):
             self.process(func.clauses.clauses[2], **kw)
         )
 
+    def limit_by_clause(self, select, **kw):
+        text = ''
+        limit_by_clause = select._limit_by_clause
+        if limit_by_clause:
+            text += ' LIMIT '
+            if limit_by_clause.offset is not None:
+                text += self.process(limit_by_clause.offset, **kw) + ', '
+            text += self.process(limit_by_clause.limit, **kw)
+            limit_by_exprs = limit_by_clause.by_clauses._compiler_dispatch(
+                self, **kw,
+            )
+            text += ' BY ' + limit_by_exprs
+
+        return text
+
     def limit_clause(self, select, **kw):
         text = ''
         if select._limit_clause is not None:
@@ -277,6 +292,11 @@ def _compose_select_body(
         if select._order_by_clause.clauses:
             text += self.order_by_clause(select, **kwargs)
 
+        limit_by_clause = getattr(select, '_limit_by_clause', None)
+
+        if limit_by_clause is not None:
+            text += self.limit_by_clause(select, **kwargs)
+
         if (select._limit_clause is not None or
                 select._offset_clause is not None):
             text += self.limit_clause(select, **kwargs)

clickhouse_sqlalchemy/ext/clauses.py

@@ -1,10 +1,12 @@
 from sqlalchemy import util, exc
 from sqlalchemy.sql import type_api
 from sqlalchemy.sql.elements import (
+    _literal_as_label_reference,
     BindParameter,
     ColumnElement,
     ClauseList
 )
+from sqlalchemy.sql.selectable import _offset_or_limit_clause
 from sqlalchemy.sql.visitors import Visitable
 
 
@@ -29,6 +31,19 @@ def sample_clause(element):
         return SampleParam(None, element, unique=True)
 
 
+class LimitByClause:
+
+    def __init__(self, by_clauses, offset, limit):
+        self.by_clauses = ClauseList(
+            *by_clauses, _literal_as_text=_literal_as_label_reference,
+        )
+        self.offset = _offset_or_limit_clause(offset)
+        self.limit = _offset_or_limit_clause(limit)
+
+    def __bool__(self):
+        return bool(self.by_clauses.clauses)
+
+
 class Lambda(ColumnElement):
     """Represent a lambda function, ``Lambda(lambda x: 2 * x)``."""
 

clickhouse_sqlalchemy/orm/query.py

@@ -7,15 +7,17 @@
 from sqlalchemy.orm.util import _ORMJoin as _StandardORMJoin
 
 from ..ext.clauses import (
-    sample_clause,
     ArrayJoin,
+    LimitByClause,
+    sample_clause,
 )
 
 
 class Query(BaseQuery):
     _with_totals = False
     _final = None
     _sample = None
+    _limit_by = None
     _array_join = None
 
     def _compile_context(self, labels=True):
@@ -25,6 +27,7 @@ def _compile_context(self, labels=True):
         statement._with_totals = self._with_totals
         statement._final_clause = self._final
         statement._sample_clause = sample_clause(self._sample)
+        statement._limit_by_clause = self._limit_by
         statement._array_join = self._array_join
 
         return context
@@ -51,6 +54,9 @@ def final(self):
     def sample(self, sample):
         self._sample = sample
 
+    @_generative()
+    def limit_by(self, *by_clauses, offset=None, limit):
+        self._limit_by = LimitByClause(by_clauses, offset, limit)
 
     def join(self, *props, **kwargs):
         type = kwargs.pop('type', None)

clickhouse_sqlalchemy/sql/selectable.py

@@ -4,7 +4,11 @@
     Join as StandardJoin,
 )
 
-from ..ext.clauses import ArrayJoin, sample_clause
+from ..ext.clauses import (
+    ArrayJoin,
+    LimitByClause,
+    sample_clause,
+)
 
 
 __all__ = ('Select', 'select')
@@ -30,6 +34,7 @@ class Select(StandardSelect):
     _with_totals = False
     _final_clause = None
     _sample_clause = None
+    _limit_by_clause = None
     _array_join = None
 
     @_generative
@@ -44,6 +49,10 @@ def final(self):
     def sample(self, sample):
         self._sample_clause = sample_clause(sample)
 
+    @_generative
+    def limit_by(self, *by_clauses, offset=None, limit):
+        self._limit_by_clause = LimitByClause(by_clauses, offset, limit)
+
     @_generative
     def array_join(self, *columns):
         self._array_join = ArrayJoin(*columns)

tests/orm/test_select.py

@@ -103,6 +103,21 @@ def test_final(self):
             'SELECT t1.x AS t1_x FROM t1 FINAL GROUP BY t1.x'
         )
 
+    def test_limit_by(self):
+        table = self._make_table()
+
+        query = self.session.query(table.c.x).order_by(table.c.x)\
+            .limit_by(table.c.x, limit=1)
+        self.assertEqual(
+            self.compile(query),
+            'SELECT t1.x AS t1_x FROM t1 ORDER BY t1.x '
+            'LIMIT %(param_1)s BY t1.x'
+        )
+        self.assertEqual(
+            self.compile(query, literal_binds=True),
+            'SELECT t1.x AS t1_x FROM t1 ORDER BY t1.x LIMIT 1 BY t1.x'
+        )
+
     def test_lambda_functions(self):
         query = self.session.query(
             func.arrayFilter(

tests/sql/test_selectable.py

@@ -57,6 +57,20 @@ def test_final(self):
             'SELECT t1.x FROM t1 FINAL GROUP BY t1.x'
         )
 
+    def test_limit_by(self):
+        table = self._make_table()
+
+        query = select([table.c.x]).order_by(table.c.x)\
+            .limit_by(table.c.x, limit=1)
+        self.assertEqual(
+            self.compile(query),
+            'SELECT t1.x FROM t1 ORDER BY t1.x LIMIT %(param_1)s BY t1.x'
+        )
+        self.assertEqual(
+            self.compile(query, literal_binds=True),
+            'SELECT t1.x FROM t1 ORDER BY t1.x LIMIT 1 BY t1.x'
+        )
+
     def test_nested_type(self):
         table = self._make_table(
             't1',