面试题与答案

The import command in Sqoop is used to import data from a relational database into Hadoop.

Example:

sqoop import --connect jdbc:mysql://localhost:3306/db --table mytable --target-dir /user/hadoop/mytable

Incremental imports in Sqoop can be done using the --incremental option. You need to specify the mode and the column to use for tracking changes.

Example:

sqoop import --connect jdbc:mysql://localhost:3306/db --table mytable --incremental append --check-column id --last-value 100

The export command in Sqoop is used to export data from Hadoop to a relational database.

Example:

sqoop export --connect jdbc:mysql://localhost:3306/db --table mytable --export-dir /user/hadoop/mytable

The metastore in Sqoop is a central repository that stores metadata related to Sqoop jobs, such as saved jobs, connection information, and job history.

The --map-column-java option allows you to specify how the columns from the database table should be mapped to Java types during import.

Example:

sqoop import --connect jdbc:mysql://localhost:3306/db --table mytable --map-column-java id=String,value=Double

In free-form query import, you can specify a SQL query to extract data, while in table-based import, you directly import an entire table.

The --merge-key option is used during the Sqoop merge operation to specify the columns used for identifying rows to merge.

The --query option allows you to specify a SQL SELECT statement to retrieve data during Sqoop import.

Example:

sqoop import --connect jdbc:mysql://localhost:3306/db --query SELECT * FROM mytable WHERE $CONDITIONS --split-by id

The --boundary-query option allows you to specify a SQL query that is used to determine the range of values for the splitting column.

Example:

sqoop import --connect jdbc:mysql://localhost:3306/db --table mytable --boundary-query SELECT MIN(id), MAX(id) FROM mytable

The --boundary-query option allows you to specify a SQL query that is used to determine the range of values for the splitting column.

Example:

sqoop import --connect jdbc:mysql://localhost:3306/db --table mytable --boundary-query SELECT MIN(id), MAX(id) FROM mytable

You can import data into Hive using Sqoop by specifying the --hive-import option along with the target Hive table using --hive-table.

Example:

sqoop import --connect jdbc:mysql://localhost:3306/db --table mytable --hive-import --hive-table myhivetable

The --hive-overwrite option in Sqoop is used to overwrite existing data in the Hive table during import.

Example:

sqoop import --connect jdbc:mysql://localhost:3306/db --table mytable --hive-import --hive-table myhivetable --hive-overwrite

To update existing records during export in Sqoop, you can use the --update-key option along with --update-mode option set to allowinsert.

Example:

sqoop export --connect jdbc:mysql://localhost:3306/db --table mytable --update-key id --update-mode allowinsert --export-dir /user/hadoop/mytable

The --hcatalog-database option specifies the HCatalog database name when importing data into HCatalog.

Example:

sqoop import --connect jdbc:mysql://localhost:3306/db --table mytable --hcatalog-import --hcatalog-database mydatabase