-- 在目标主库执行；仅新增养生课程「正在学习人数」字段，不修改已有业务数据，可重复执行。
SET @ddl = IF(
    (SELECT COUNT(*) FROM information_schema.COLUMNS
     WHERE TABLE_SCHEMA = DATABASE() AND TABLE_NAME = 'tcm_health_course'
       AND COLUMN_NAME = 'studying_count') = 0,
    'ALTER TABLE tcm_health_course ADD COLUMN studying_count INT NOT NULL DEFAULT 0 COMMENT ''正在学习人数'' AFTER learn_user_count',
    'SELECT 1');
PREPARE stmt FROM @ddl;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;