AstBuilder中有一个visitQuery方法，这是与SQL中SELECT查询语法最紧密的接口实现，这个方法会调用其他一些方法，最终返回LogicPlan类型。LogicPlan是Spark内部的逻辑计划表示，其本身是一个树形结构，可以理解为AST的一个具体实现。在visitQuery方法中，有一部分是withQueryResultClauses，这部分就是对查询结果从句的处理。...
"""spark.sql(query).show()# Give the number of the bad row as an integerbad_row=7# Provide the missing clause, SQL keywords in upper caseclause='PARTITION BY train_id' 点表示法dataframe实现 聚合函数 # Give the identical result in each commandspark.sql('SELECT train_id, MIN(time) AS...
先来一个sql:SELECT NAME FROM NAME LEFT JOIN NAME2 ON NAME = NAME JOIN NAME3 ON NAME = NAME这条sql形成的逻辑算子树为:上图的树结构的生成;主要关注join部分就可以;其源码在AstBuilder中:1 2 3 4 5 6 7 8 override def visitFromClause(ctx: FromClauseContext): LogicalPlan = withOrigin(ctx)...
spark.sql.orc.filterPushdown FALSE When true, enable filter pushdown for ORC files. spark.sql.orderByOrdinal TRUE When true, the ordinal numbers are treated as the position in the select list. When false, the ordinal numbers in order/sort by clause are ignored. spark.sql.parquet.binaryAsStri...
spark.sqlContext.sql(sqlText) // #2 1. 2. 3. def sql(sqlText: String): DataFrame = sparkSession.sql(sqlText) /** * Executes a SQL query using Spark, returning the result as a `DataFrame`. * The dialect that is used for SQL parsing can be configured with 'spark.sql.dialect'. ...
从visitSingleStatement为入口从根部递归访问整棵树,当访问到某个子节点可以构造LogicalPlan时,然后传递到父节点;执行到QuerySpecificationContext时,首先访问FromClauseContext子树,生成from的LogicalPlan,然后调用withQuerySpecification在from的基础上完成扩展 从访问QuerySpecificationContext开始,主要分为以下三个步骤 ...
direction_clause 定义抓取数据的方向。取值范围：NEXT（缺省值）从当前关联位置开始，抓取下一行。PRIOR ...
3、强撸调试,visitRegularQuerySpecification、visitFromClause、AstBuilder.visitTableName详解、withSelectQuerySpecification等等,整个链路手把手调试,让大家熟悉调试的过程和感觉 4、总结迭代方法,调试技巧 4、复习&答疑&问题总结&作业 大家平时有问题都在群里问了,但比较散,来一次总结和作业讲解 ...
代码位于org.apache.spark.sql.execution.Aggregation类中,这段注释的大概意思是,尽管functionsWithDistinct可以包含多个dinstinct聚合函数,但是所有的distinct聚合函数是作用在同一列上,例如[COUNT(DISTINCT foo), MAX(DISTINCT foo)];否则就是不合法的,例如[COUNT(DISTINCT bar), COUNT(DISTINCT foo)],是不合法的。
SQL RLIKE expression (LIKE with Regex). Returns a boolean column based on a regex match. StartsWith(Column) String starts with. Returns a boolean column based on a string match. StartsWith(String) String starts with another string literal. Returns a boolean column based on a string match. ...