Sqoop Import control arguments:

Argument	Description
--append	Append data to an existing dataset in HDFS
--as-avrodatafile	Imports data to Avro Data Files
--as-sequencefile	Imports data to SequenceFiles
--as-textfile	Imports data as plain text (default)
--boundary-query <statement>	Boundary query to use for creating splits
--columns <col,col,col…>	Columns to import from table
--direct	Use direct import fast path
--direct-split-size <n>	Split the input stream every n bytes when importing in direct mode
--inline-lob-limit <n>	Set the maximum size for an inline LOB
-m,--num-mappers <n>	Use n map tasks to import in parallel
-e,--query <statement>	Import the results of statement.
--split-by <column-name>	Column of the table used to split work units
--table <table-name>	Table to read
--target-dir <dir>	HDFS destination dir
--warehouse-dir <dir>	HDFS parent for table destination
--where <where clause>	WHERE clause to use during import
-z,--compress	Enable compression
--compression-codec <c>	Use Hadoop codec (default gzip)
--null-string <null-string>	The string to be written for a null value for string columns
--null-non-string <null-string>	The string to be written for a null value for non-string columns

The --null-string and --null-non-string arguments are optional.\ If not specified, then the string "null" will be used.

Source: https://sqoop.apache.org/docs