关于sql:SQL-saveOrUpdate

MySQL：ON DUPLICATE KEY UPDATE
参考 https://blog.csdn.net/qq_2277…

PostgreSQL：ON CONFLICT
参考 https://blog.csdn.net/weixin_…

MyBatis：

<selectKey keyProperty="count" resultType="int" order="BEFORE">
    select count(1) as count from xxx where aaa=1
</selectKey>
<if test="count > 0">
    update set xxx
</if>
<if test="count == 0">
    INSERT INTO xxx
</if>

Ps：MyBatis的形式在遇到并发插入报反复key时，能够用重试的形式解决