Render VALUES within composed MySQL on duplicate key expressions

Fixed issue in MySQL :meth:`.mysql.Insert.on_duplicate_key_update` construct
where using a SQL function or other composed expression for a column argument
would not properly render the ``VALUES`` keyword surrounding the column
itself.

Fixes: #5173
Change-Id: I16d39c2fdb8bbb7f3d1b2ffdd20e1bf69359ab75

1 files changed, 25 insertions, 9 deletions

diff --git a/lib/sqlalchemy/dialects/mysql/base.py b/lib/sqlalchemy/dialects/mysql/base.py
index 6ea8cbcb8..a97719532 100644
--- a/lib/sqlalchemy/dialects/mysql/base.py
+++ b/lib/sqlalchemy/dialects/mysql/base.py
@@ -743,6 +743,8 @@ from collections import defaultdict
 import re
 import sys
 
+from sqlalchemy import literal_column
+from sqlalchemy.sql import visitors
 from . import reflection as _reflection
 from .enumerated import ENUM
 from .enumerated import SET
@@ -1303,17 +1305,31 @@ class MySQLCompiler(compiler.SQLCompiler):
             if coercions._is_literal(val):
                 val = elements.BindParameter(None, val, type_=column.type)
                 value_text = self.process(val.self_group(), use_schema=False)
-            elif isinstance(val, elements.BindParameter) and val.type._isnull:
-                val = val._clone()
-                val.type = column.type
-                value_text = self.process(val.self_group(), use_schema=False)
-            elif (
-                isinstance(val, elements.ColumnClause)
-                and val.table is on_duplicate.inserted_alias
-            ):
-                value_text = "VALUES(" + self.preparer.quote(column.name) + ")"
             else:
+
+                def replace(obj):
+                    if (
+                        isinstance(obj, elements.BindParameter)
+                        and obj.type._isnull
+                    ):
+                        obj = obj._clone()
+                        obj.type = column.type
+                        return obj
+                    elif (
+                        isinstance(obj, elements.ColumnClause)
+                        and obj.table is on_duplicate.inserted_alias
+                    ):
+                        obj = literal_column(
+                            "VALUES(" + self.preparer.quote(column.name) + ")"
+                        )
+                        return obj
+                    else:
+                        # element is not replaced
+                        return None
+
+                val = visitors.replacement_traverse(val, {}, replace)
                 value_text = self.process(val.self_group(), use_schema=False)
+
             name_text = self.preparer.quote(column.name)
             clauses.append("%s = %s" % (name_text, value_text))