How Does SparkSQL Handle Subqueries in Different Versions?

SparkSQL Support for Subqueries

In Spark, subqueries are currently supported in limited forms. Spark 2.0 and later versions offer expanded support for subqueries, including both correlated and uncorrelated variants. However, in Spark versions prior to 2.0, subqueries are only allowed in the FROM clause, similar to Hive versions 0.12 and earlier.

Subquery in WHERE Clause Error

The error encountered when running the provided query in the Spark shell is due to the fact that subqueries in the WHERE clause are not supported in Spark prior to version 2.0. The error highlights that the parser expected a parenthesis but encountered the MAX function instead, indicating that the syntax is incorrect.

Support in Spark 2.0

In Spark 2.0 and later, subqueries can be used in both the FROM and WHERE clauses. The provided query can be rewritten as follows:

sqlContext.sql("select sal from samplecsv where sal < (select max(sal) from samplecsv)").collect().foreach(println)

Limitations in Spark < 2.0

In Spark versions prior to 2.0, subqueries are only supported in the FROM clause. Correlated subqueries, in which the subquery references columns from the outer query, are not supported. To achieve similar functionality, cartesian joins must be used instead.

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