Allow delete where clause to refer multiple tables.

Implemented "DELETE..FROM" syntax for Postgresql, MySQL, MS SQL Server
(as well as within the unsupported Sybase dialect) in a manner similar
to how "UPDATE..FROM" works.  A DELETE statement that refers to more than
one table will switch into "multi-table" mode and render the appropriate
"USING" or multi-table "FROM" clause as understood by the database.
Pull request courtesy Pieter Mulder.

For SQL syntaxes see:

Postgresql: https://www.postgresql.org/docs/current/static/sql-delete.html
MySQL: https://dev.mysql.com/doc/refman/5.7/en/delete.html#multiple-table_syntax
MSSQL: https://docs.microsoft.com/en-us/sql/t-sql/statements/delete-transact-sql
Sybase: http://infocenter.sybase.com/help/index.jsp?topic=/com.sybase.infocenter.dc00801.1510/html/iqrefso/X315721.htm

Co-authored by: Mike Bayer <mike_mp@zzzcomputing.com>
Change-Id: I6dfd57b49e44a095d076dc493cd2360bb5d920d3
Pull-request: https://github.com/zzzeek/sqlalchemy/pull/392
Fixes: #959

1 files changed, 18 insertions, 0 deletions

diff --git a/lib/sqlalchemy/dialects/sybase/base.py b/lib/sqlalchemy/dialects/sybase/base.py
index 5d2f0f70c..0d7d03e78 100644
--- a/lib/sqlalchemy/dialects/sybase/base.py
+++ b/lib/sqlalchemy/dialects/sybase/base.py
@@ -369,6 +369,24 @@ class SybaseSQLCompiler(compiler.SQLCompiler):
         else:
             return ""
 
+    def delete_table_clause(self, delete_stmt, from_table,
+                            extra_froms):
+        """If we have extra froms make sure we render any alias as hint."""
+        ashint = False
+        if extra_froms:
+            ashint = True
+        return from_table._compiler_dispatch(
+            self, asfrom=True, iscrud=True, ashint=ashint
+        )
+
+    def delete_extra_from_clause(self, delete_stmt, from_table,
+                                 extra_froms, from_hints, **kw):
+        """Render the DELETE .. FROM clause specific to Sybase."""
+        return "FROM " + ', '.join(
+            t._compiler_dispatch(self, asfrom=True,
+                                 fromhints=from_hints, **kw)
+            for t in [from_table] + extra_froms)
+
 
 class SybaseDDLCompiler(compiler.DDLCompiler):
     def get_column_specification(self, column, **kwargs):