07 2017 档案

All you need to know about sorting in Postgres
摘要：按：之前看pg的执行计划，多次看到不同的排序方式，但不知何意。偶遇此篇讲解pg执行计划三种排序方式，备忘一下。 Sorting Sorting is one of the most fundamental operations in database systems and understandin 阅读全文

posted @ 2017-07-25 16:43 Still water run deep 阅读(325) 评论(0) 推荐(0)

Indexing GROUP BY
摘要：SQL databases use two entirely different group by algorithms. The first one, the hash algorithm, aggregates the input records in a temporary hash tabl 阅读全文

posted @ 2017-07-24 15:39 Still water run deep 阅读(222) 评论(0) 推荐(0)

What is the bitmap index?
摘要：示例执行计划： > what does "Bitmap Heap Scan" phase do? A plain indexscan fetches one tuple-pointer at a time from the index,and immediately visits that tupl 阅读全文

posted @ 2017-07-19 15:26 Still water run deep 阅读(380) 评论(0) 推荐(0)

导航