At present, Oceanbase only implements one cost based query rewriting (or expansion). In fact, many advanced rewriting rules in the database (such as complex view merge and window function rewriting) need to be rewritten based on cost
Or expansion rewrites a query into several sub queries composed of union. This rewrite may provide better optimization space for each sub query, but it will also lead to the execution of multiple sub queries. Therefore, this rewrite needs to be judged based on the cost.
This article is written by Ji Changxin Author, article address: https://blog.isoyu.com/archives/oceanbasejiyudaijiadechaxungaixieor-expansion.html
use Knowledge Sharing Attribution 4.0 International License Agreement. Unless the reprint/source is indicated, they are all original or translated by this website. Please sign your name before reprinting. Last editing time: September 16, 2018 at 04:36 p.m