Allow dialects to customize group by clause compilation

Refactored :class:`.SQLCompiler` to expose a
:meth:`.SQLCompiler.group_by_clause` method similar to the
:meth:`.SQLCompiler.order_by_clause` and :meth:`.SQLCompiler.limit_clause`
methods, which can be overridden by dialects to customize how GROUP BY
renders.  Pull request courtesy Samuel Chou.

Change-Id: I0a7238e55032558c27a0c56a72907c7b883456f1
Pull-request: https://github.com/zzzeek/sqlalchemy/pull/474

1 files changed, 37 insertions, 0 deletions

diff --git a/test/sql/test_compiler.py b/test/sql/test_compiler.py
index 7f2c44bf1..993008c07 100644
--- a/test/sql/test_compiler.py
+++ b/test/sql/test_compiler.py
@@ -28,6 +28,7 @@ from sqlalchemy.sql.expression import ClauseList, _literal_as_text, HasPrefixes
 from sqlalchemy.engine import default
 from sqlalchemy.dialects import mysql, mssql, postgresql, oracle, \
     sqlite, sybase
+from sqlalchemy.dialects.postgresql.base import PGCompiler, PGDialect
 from sqlalchemy.ext.compiler import compiles
 from sqlalchemy.sql import compiler
 
@@ -1297,6 +1298,42 @@ class SelectTest(fixtures.TestBase, AssertsCompiledSQL):
             "GROUP BY myothertable.othername ORDER BY myothertable.othername"
         )
 
+    def test_custom_order_by_clause(self):
+        class CustomCompiler(PGCompiler):
+            def order_by_clause(self, select, **kw):
+                return super(CustomCompiler, self).\
+                    order_by_clause(select, **kw) + " CUSTOMIZED"
+
+        class CustomDialect(PGDialect):
+            name = 'custom'
+            statement_compiler = CustomCompiler
+
+        stmt = select([table1.c.myid]).order_by(table1.c.myid)
+        self.assert_compile(
+            stmt,
+            "SELECT mytable.myid FROM mytable ORDER BY "
+            "mytable.myid CUSTOMIZED",
+            dialect=CustomDialect()
+        )
+
+    def test_custom_group_by_clause(self):
+        class CustomCompiler(PGCompiler):
+            def group_by_clause(self, select, **kw):
+                return super(CustomCompiler, self).\
+                    group_by_clause(select, **kw) + " CUSTOMIZED"
+
+        class CustomDialect(PGDialect):
+            name = 'custom'
+            statement_compiler = CustomCompiler
+
+        stmt = select([table1.c.myid]).group_by(table1.c.myid)
+        self.assert_compile(
+            stmt,
+            "SELECT mytable.myid FROM mytable GROUP BY "
+            "mytable.myid CUSTOMIZED",
+            dialect=CustomDialect()
+        )
+
     def test_for_update(self):
         self.assert_compile(
             table1.select(table1.c.myid == 7).with_for_update(),