1.关联查询更新，时间相加，相减
UPDATE contractpaymentagree ca , contractwarn cw
SET ca.noticeDate =(
SELECT
DATE_SUB(
ca.planDate,
INTERVAL cw.warnDay DAY
)
)
WHERE
ca.companyId = cw.companyId
AND cw.isOn = 1
2.增加字段
ALTER TABLE t_Name ADD COLUMN c_name decimal(14,2) COMMENT '单价';
3.修改字段
alter table Contract modify column contractNo varchar(30) COMMENT '合同编号';