-- 执行于部署个人资料接口之前，可重复执行。
SET @profile_column_exists = (
    SELECT COUNT(*) FROM information_schema.COLUMNS
    WHERE TABLE_SCHEMA = DATABASE() AND TABLE_NAME = 'app_user'
      AND COLUMN_NAME = 'signature'
);
SET @profile_sql = IF(@profile_column_exists = 0,
    'ALTER TABLE app_user ADD COLUMN signature VARCHAR(200) NOT NULL DEFAULT '''' COMMENT ''个性签名''',
    'SELECT 1');
PREPARE profile_statement FROM @profile_sql;
EXECUTE profile_statement;
DEALLOCATE PREPARE profile_statement;