Can a JDBC query be put in parentheses in Spark?
A query to be used to read data into Spark. The specified query will be enclosed in parentheses and used as a subquery in the FROM clause. Spark will also alias the subquery clause. As an example, Spark will issue a query of the following form to the JDBC source. Below are a couple of restrictions when using this option.
Table of Contents
Which is better JDBC or jdbcrdd in spark?
This functionality should be preferred over using JdbcRDD. This is because the results are returned as a DataFrame and can easily be processed in Spark SQL or joined with other data sources. The JDBC datasource is also easier to use from Java or Python, since it doesn’t require the user to provide a ClassTag.
When to use savemode.overwrite in spark?
When SaveMode.Overwrite is enabled, this option causes Spark to truncate an existing table instead of dropping and recreating it. This can be more efficient and prevents table metadata (eg indexes) from being removed. However, it won’t work in some cases, such as when the new data has a different schema.
Can you specify dbtable and query in spark?
Specifying dbtable and query options at the same time is not allowed. A query to be used to read data into Spark. The specified query will be enclosed in parentheses and used as a subquery in the FROM clause. Spark will also alias the subquery clause.
A query to be used to read data into Spark. The specified query will be enclosed in parentheses and used as a subquery in the FROM clause. Spark will also alias the subquery clause. As an example, Spark will issue a query of the following form to the JDBC source. Below are a couple of restrictions when using this option.
How to load data from MySQL in spark?
We have data in an RDBMS table, let’s say MySQL table. The requirement is to load data from MySQL into Spark using a JDBC connection. Sample Data We will use the following sample data that contains the basic details of an employee, such as employee number, employee name, designation, manager, hire date, salary, and department.
How to read data from DB in spark in parallel?
Saurabh, to read in parallel using the standard Spark JDBC data source support, you need to use the numPartitions option as you’d expect. But you should give Spark some clue how to split the read SQL statements into multiple parallel ones.
How to limit reading data from a table in spark?
After registering the table, you can limit the data reading using your Spark SQL query using a WHERE clause. If this isn’t an option, you can use a view instead, or as described in this post, you can also use any arbitrary subquery as input to the table.