At the time of writing this book, Impala's latest version, 1.1.x, does not support the following SQL features, which are available in HiveQL:
Nonscalar data types such as maps, array, and struct
XML and JSON functions
The LOAD DATA statement to load raw files
Custom UDF, User Defined Aggregation Functions (UDAF), and User Defined Table Generating Functions (UDTF) up to Cloudera Impala 1.1.x. Please check Appendix, Technology Behind Impala and Integration with Third-party Applications, on support for these functions in Impala 1.2.0 Beta.
Sampling, Lateral Views, Roles, Custom SerDes, and Multiple DISTINCT
Here is a list of HiveQLstatements that are not supported in Impala: