有这样一个疑问,如果是一系列比较复杂的操作,跨表、累加之类的,简单的 sql 可能需要执行两个以上才能完成。
用编程语言多次执行,结果集里面折腾有效率呢;还是想尽办法写个高深的 sql,一次解决问题呢?
俺 sql 很水,编程语言也只是中下游水平,又有一颗追求优雅、高效之心。
举个例子:
有个临时表,存储 pid, tid, duration,通过一次 select,将 (pid, tid) 作为唯一组合,统计其出现次数(count),和 duration 累加总和。
然后将 pid, tid, count, duration 存入另外一个表,还要保证另外一个表的 (pid, tid) 是唯一组合。
插入部分的唯一性已经写出了稍微复杂的 sql,现在在考虑是将第一部分的结果集遍历再分别插入,还是再考虑一个更复杂的 sql。
ps: 第二部分插入的题目在:http://segmentfault.com/q/1010000000723454
所用的 sql 为:
<code>alter table stat add unique index pid_and_tid (pid, tid); insert into stat (pid, tid, count, duration) values (1, 1, 1, 1) on duplicate key update count = count + 1, duration = duration + 1 </code>
回复内容:
有这样一个疑问,如果是一系列比较复杂的操作,跨表、累加之类的,简单的 sql 可能需要执行两个以上才能完成。
用编程语言多次执行,结果集里面折腾有效率呢;还是想尽办法写个高深的 sql,一次解决问题呢?
俺 sql 很水,编程语言也只是中下游水平,又有一颗追求优雅、高效之心。
举个例子:
有个临时表,存储 pid, tid, duration,通过一次 select,将 (pid, tid) 作为唯一组合,统计其出现次数(count),和 duration 累加总和。
然后将 pid, tid, count, duration 存入另外一个表,还要保证另外一个表的 (pid, tid) 是唯一组合。
插入部分的唯一性已经写出了稍微复杂的 sql,现在在考虑是将第一部分的结果集遍历再分别插入,还是再考虑一个更复杂的 sql。
ps: 第二部分插入的题目在:http://segmentfault.com/q/1010000000723454
所用的 sql 为:
<code>alter table stat add unique index pid_and_tid (pid, tid); insert into stat (pid, tid, count, duration) values (1, 1, 1, 1) on duplicate key update count = count + 1, duration = duration + 1 </code>
几乎任何时候降低数据库的
计算复杂度
都是好的。
内存可重复利用,容易扩展,在大多数场景下都可以利用内存来换取数据库性能,即:从数据库中简单地取出数据,再在内存中处理成想要的数据。

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