一、引言 在数据库系统中,SQL 查询性能直接影响业务响应速度。GaussDB 作为一款高性能分布式数据库,其 EXPLAIN ANALYZE 工具能够深入解析查询的执行过程,暴露潜在的性能瓶颈。本文将从执行计划的生成逻辑、关键字段解读、优化策略到实战案例,全面剖析这一核心技术。 二、EXPLAIN ANALYZE 工作原理 执行计划生成机...
如果不想为包含 GROUP BY 子句的查询进行排序,需要显式的写上 ORDER BY NULL。Using filesort:有一些情况下对结果集中的记录进行排序是可以使用到索引的。这个查询语句可以利用 idx_order_no 索引直接取出 order_no 列的 10 条记录,然后再进行回表操作。但是很多情况下排序操作无法使用到索引,只能在内存中或者磁盘...
the lines of action of the forces do not intersect at a single point. this type of force system requires additional considerations such as moments and couples to determine the overall effect on the object. an example of a non-concurrent force system is the forces acting on a beam or a tru...
In this example, my_decorator is a function that takes another function func as an argument and returns a new function wrapper that wraps func with some additional behavior. The resulting wrapper function can be called just like func, but with the added behavior provided by my_decorator. Using...