mysql语句入门详解

本文主要和大家分享mysql语句入门详解，专门和大家一步一步详解mysql语句，希望能帮助到大家。

Select,Left Join的用法,及模糊查询的实现：

LEFT JOIN 关键字会从左表 (table_name1) 那里返回所有的行，即使在右表 (table_name2) 中没有匹配的行。
（业务需求：从一张表查询出来的数据要关联到另一个表，并实现模糊查询）

const sql = `select cei.intentionID,cei.engineerName,cei.nickname,cei.headImgUrl,
ifnull(cmw.headImgUrl,'') inviteImgUrl,ifnull(cmw.nickname,'') inviteNickName
from cm_engineer_intentions cei
left join cm_member_wechats cmw on cmw.referralCode=cei.inviteCode
where (:isGrant=-1 or isGrant=:isGrant)
and (:intentionStatus=-1 or intentionStatus=:intentionStatus)
and (:searchKey='' or concat(engineerMobile,engineerName) like concat('%',:searchKey,'%'))
order by intentionStatus asc,createTime desc`;

Update Set的用法

(业务需求：当某个字段有传进来时就更新，没有传进来时忽略,这样可以根据你的需求来选择是否插入某个字段)

const contactRemarkSql = isUpdateRemark ? ',contactRemark=:contactRemark' : '';
const sql = `update cm_engineer_intentions
set intentionStatus=:intentionStatus ${contactRemarkSql}
where intentionID=:intentionID`;

Delete,In的用法：(IN 操作符允许我们在WHERE子句中规定多个值)

下面的SQL语句可以删除多条符合条件的数据
(业务需求: 进行删除操作时，创建数据的人若是操作数据的人，则删除，否则更新状态)
const deleteSql = delete from cm_fast_order_goods where orderGoodsID in (${deleteData.deleteIDs}) and createUser=:userName;
const updateSql = update cm_fast_order_goods set status=0 where orderGoodsID in (${deleteData.deleteIDs}) and createUser!=:userName;

Insert的用法

(业务需求：新增一条新的数据)

const sqlOrderEngineer = `insert into cm_order_engineers
(orderEngineerID,orderGoodsID,orderID,engineerID,engineerName,createUser,createTime)
values
(:orderEngineerID,:orderGoodsID,:orderID,:engineerID,:engineerName,:createUser,:createTime)

(业务需求：每新增一条数据，某一字段在原有的数据的最大值基础上+1)

const sql = `insert into cm_engineers
(engineerCode,loginName,password,engineerName,sex,birthDate,status,createUser,createTime)
select                            
ifnull(max(engineerCode),0)+1,:loginName,:password,:engineerName,:sex,:birthDate,
:status,:createUser,now()
from cm_engineers`;

(业务需求：从其他表中新增数据到当前表)

insert into cm_fast_order_goods (orderGoodsID,orderID,goodsID,goodsCode,goodsPicUrl,createUser,createTime)
select :orderGoodsID,:orderID,:goodsID,goodsCode,iconUrl,:createUser,now()
from cm_service_goods
where goodsID=:goodsID and status=1

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