SET @column_exists := (
    SELECT COUNT(1)
    FROM information_schema.COLUMNS
    WHERE TABLE_SCHEMA = DATABASE()
      AND TABLE_NAME = 't_site'
      AND COLUMN_NAME = 'venue_partner_id'
);

SET @ddl := IF(
    @column_exists = 0,
    'ALTER TABLE `t_site` ADD COLUMN `venue_partner_id` int NULL DEFAULT NULL COMMENT ''场地方合作商ID'' AFTER `partner_id`',
    'SELECT 1'
);

PREPARE stmt FROM @ddl;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;