lib/Doctrine/DBAL/Platforms/SQLServerPlatform.php
protected function getAlterColumnCommentSQL($tableName, $columnName, $comment)
    {
        if (strpos($tableName, '.') !== false) {
            [$schemaSQL, $tableSQL] = explode('.', $tableName);
            $schemaSQL              = $this->quoteStringLiteral($schemaSQL);
            $tableSQL               = $this->quoteStringLiteral($tableSQL);
        } else {
            $schemaSQL = "'dbo'";
            $tableSQL  = $this->quoteStringLiteral($tableName);
        }

        return $this->getUpdateExtendedPropertySQL(
            'MS_Description',
            $comment,
            'SCHEMA',
            $schemaSQL,
            'TABLE',
            $tableSQL,
            'COLUMN',
            $columnName
        );
    }
protected function getAlterColumnCommentSQL($tableName, $columnName, $comment)
    {
        if (strpos($tableName, '.') !== false) {
            [$schemaSQL, $tableSQL] = explode('.', $tableName);
            $schemaSQL              = $this->quoteStringLiteral($schemaSQL);
            $tableSQL               = $this->quoteStringLiteral($tableSQL);
        } else {
            $schemaSQL = "'dbo'";
            $tableSQL  = $this->quoteStringLiteral($tableName);
        }

        return $this->getUpdateExtendedPropertySQL(
            'MS_Description',
            $comment,
            'SCHEMA',
            $schemaSQL,
            'TABLE',
            $tableSQL,
            'COLUMN',
            $columnName
        );
    }
protected function getAlterColumnCommentSQL ( $ tableName , $ columnName , $ comment ) { if ( strpos ( $ tableName , '.' ) !== false ) { [ $ schemaSQL , $ tableSQL ] = explode ( '.' , $ tableName ) ; $ schemaSQL = $ this -> quoteStringLiteral ( $ schemaSQL ) ; $ tableSQL = $ this -> quoteStringLiteral ( $ tableSQL ) ; } else { $ schemaSQL = "'dbo'" ; $ tableSQL = $ this -> quoteStringLiteral ( $ tableName ) ; } return $ this -> getUpdateExtendedPropertySQL ( 'MS_Description' , $ comment , 'SCHEMA' , $ schemaSQL , 'TABLE' , $ tableSQL , 'COLUMN' , $ columnName ) ; }
Returns the SQL statement for altering a column comment.

SQL Server does not support native column comments,
therefore the extended properties functionality is used
as a workaround to store them.
The property name used to store column comments is "MS_Description"
which provides compatibility with SQL Server Management Studio,
as column comments are stored in the same property there when
specifying a column's "Description" attribute.

@param string      $tableName  The quoted table name to which the column belongs.
@param string      $columnName The quoted column name to alter the comment for.
@param string|null $comment    The column's comment.

@return string
Returns the SQL statement for altering a column comment .