- [bug] UPDATE..FROM syntax with SQL Server

requires that the updated table be present
in the FROM clause when an alias of that
table is also present in the FROM clause.
The updated table is now always present
in the FROM, when FROM is present
in the first place.  Courtesy sayap.
[ticket:2468]

2 files changed, 17 insertions, 1 deletions

diff --git a/lib/sqlalchemy/dialects/mssql/base.py b/lib/sqlalchemy/dialects/mssql/base.py
index 78da18711..3366d5fab 100644
--- a/lib/sqlalchemy/dialects/mssql/base.py
+++ b/lib/sqlalchemy/dialects/mssql/base.py
@@ -985,6 +985,22 @@ class MSSQLCompiler(compiler.SQLCompiler):
         else:
             return ""
 
+    def update_from_clause(self, update_stmt,
+                                from_table, extra_froms,
+                                from_hints,
+                                **kw):
+        """Render the UPDATE..FROM clause specific to MSSQL.
+        
+        In MSSQL, if the UPDATE statement involves an alias of the table to
+        be updated, then the table itself must be added to the FROM list as
+        well. Otherwise, it is optional. Here, we add it regardless.
+        
+        """
+        return "FROM " + ', '.join(
+                    t._compiler_dispatch(self, asfrom=True,
+                                    fromhints=from_hints, **kw)
+                    for t in [from_table] + extra_froms)
+
 class MSSQLStrictCompiler(MSSQLCompiler):
     """A subclass of MSSQLCompiler which disables the usage of bind
     parameters where not allowed natively by MS-SQL.
diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index fdff99fb1..bf234fe5c 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -1115,7 +1115,7 @@ class SQLCompiler(engine.Compiled):
         """Provide a hook to override the generation of an 
         UPDATE..FROM clause.
 
-        MySQL overrides this.
+        MySQL and MSSQL override this.
 
         """
         return "FROM " + ', '.join(