spark sql query 剖析

SQL 基本组成

Projection, Data Source, Filter

SQL 解析

SQL语句首先被Parser模块解析成Unresolved Logical Plan；
Unresolved Logical Plan通过Analyzer模块借助于Catalog中的表信息解析为Logical Plan；
Optimizer再通过各种基于规则的优化策略进行深入优化，得到Optimized Logical Plan；
优化后的逻辑执行计划依然是逻辑的，并不能被Spark系统理解，此时需要将此逻辑执行计划转换为Physical Plan。

源码探究

SessionCatalog

An internal catalog that is used by a Spark Session. This internal catalog serves as a proxy to the underlying metastore (e.g. Hive Metastore) and it also manages temporary views and functions of the Spark Session that it belongs to.
This class must be thread-safe.

UnresolvedRelation