1 . Type show tables in Hive and note down the tables .

2 . check under user/hive/warehuse/ using Hue -> File Browser or command line

that Customer folder or categories folders are already being populated .

if so  Remove it using HUE->File browser-Delete or 

Drop table command from Hive.

Then re run the script and please let me know  . 

Or 

Simply change the last line of the script 

sqoop import-all-tables \
 -m 1 \
 --connect jdbc:mysql://quickstart:3306/retail_db \
 --username=retail_dba \ --password=cloudera \ 
--compression-codec=snappy \
--as-sequencefile \
--warehouse-dir=/user/hive/warehouse \
 --hive-overwrite