Dear Wiki user, You have subscribed to a wiki page or wiki category on "Hadoop Wiki" for change notification.
The following page has been changed by ZhengShao: http://wiki.apache.org/hadoop/Hive/LanguageManual/Transform ------------------------------------------------------------------------------ Users can also plug in their own custom mappers and reducers in the data stream by using features natively supported in the Hive 2.0 language. e.g. in order to run a custom mapper script - map_script - and a custom reducer script - reduce_script - the user can issue the following command which uses the TRANSFORM clause to embed the mapper and the reducer scripts. - Note that columns will be transformed to string and deliminated by TAB before feeding to the user script, and the standard output of the user script will be treated as TAB-separated string columns. User scripts can output debug information to standard error which will be shown on the task detail page on hadoop. + Note that columns will be transformed to ''STRING'' and delimited by TAB before feeding to the user script, and the standard output of the user script will be treated as TAB-separated ''STRING'' columns. User scripts can output debug information to standard error which will be shown on the task detail page on hadoop. In the syntax, both ''MAP'' and ''REDUCE'' can be also written as ''SELECT TRANSFORM''. There are actually no difference between these three. Hive runs the reduce script in the reduce task (instead of the map task) because of the ''clusterBy''/''distributeBy''/''sortBy'' clause in the inner query.
