fix: Forge::modifyColumn() for Postgre handler

Author: michalsn

system/Database/Postgre/Forge.php

@@ -109,7 +109,7 @@ protected function _alterTable(string $alterType, string $table, $processedField
 
             if (! empty($field['default'])) {
                 $sqls[] = $sql . ' ALTER COLUMN ' . $this->db->escapeIdentifiers($field['name'])
-                    . " SET DEFAULT {$field['default']}";
+                    . " SET {$field['default']}";
             }
 
             $nullable = true; // Nullable by default.

tests/system/Database/Live/ForgeTest.php

@@ -1818,6 +1818,28 @@ public function testProcessIndexesWithForeignKeyOnly(): void
         $this->forge->dropTable('user2', true);
     }
 
+    public function testChangeDefaultFieldValueWithModifyColumn(): void
+    {
+        $this->forge->addField([
+            'delivery_sum'      => ['type' => 'int', 'constraint' => 6, 'default' => 10],
+            'delivery_free_sum' => ['type' => 'int', 'constraint' => 6, 'default' => 10],
+        ])->addKey('id', true)->createTable('test_stores', true);
+
+        $this->forge->modifyColumn('test_stores', [
+            'delivery_sum'      => ['type' => 'int', 'constraint' => 6, 'default' => 100],
+            'delivery_free_sum' => ['type' => 'int', 'constraint' => 6, 'default' => 1000],
+        ]);
+
+        $expected = ['delivery_sum' => '100', 'delivery_free_sum' => '1000'];
+
+        $fields  = $this->db->getFieldData('test_stores');
+        $results = array_column($fields, 'default', 'name');
+
+        $this->assertSame($expected, $results);
+
+        $this->forge->dropTable('test_stores', true);
+    }
+
     private function createUser2TableWithKeys(): void
     {
         $fields = [

user_guide_src/source/changelogs/v4.6.4.rst

@@ -32,6 +32,7 @@ Bugs Fixed
 
 - **Database:** Fixed a bug in ``Database::connect()`` which was causing to store non-shared connection instances in shared cache.
 - **Database:** Fixed a bug in ``Connection::getFieldData()`` for ``SQLSRV`` and ``OCI8`` where extra characters were returned in column default values (specific to those handlers), instead of following the convention used by other drivers.
+- **Forge:** Fixed a bug in ``Postgre`` and ``SQLSRV`` where changing a column's default value using ``Forge::modifyColumn()`` method produced incorrect SQL syntax.
 
 See the repo's
 `CHANGELOG.md <https://github.com/codeigniter4/CodeIgniter4/blob/develop/CHANGELOG.md>`_