Understand and implement the terminology of why partitioning the table is important and the Hive Query Language (HQL) Let me know if anything is required. Happy to help. Ping me google #bobrupakroy.

1. Hive - III
Table Partition, HQL

2. Why partitioning the table is important?
 Data is split into multiple partitions based on the values
of the conditions such as date, city, department etc.
 Data partition increases the efficiency of querying a
table.
 For example, our previous table tb_1 contains ID,
name, location, year. And if we want to retrieve only
the data with year 2010 now our query will search the
whole table for the data related to year 2010.
However if we partition the table with year and store in
a separate file and whenever a table is queried for the
year 2010 it will only read the file partitioned with year
2010 and will ignore the rest partitions. Hence it improves
the query processing time.
Rupak Roy

3. Create a partitioned Tables
hive> create table empPartitioned
(ID int, name string, location string )
Partitioned by (Year string)
Row format delimited
Fields terminated by ‘#’
Lines terminated by’n’
Stored as textfile
#note: the column values that will be used for partitioning the table must
not be defined in the table definition.
#Load the partitioned data
Hive> load data inpath ‘/home/hduser/dataset/htable2008’ overwrite
into table empPartitioned Partition(year = 2008);
Hive>load data inpath ‘/home/hduser/dataaset/htable2005’ overwrite
into table empPartitioned Partition(year= 2005);
Rupak Roy

4. Hive> Select * from empPartitioned;
Hive> Select * from empPartitioned
where year = 2005;
Hive> show partition empPartitioned;
Now this query will read only the partition with year
2005 and all other partitions will be ignored.
Rupak Roy

5. Partitioned External Table
 We can also take the advantage of external
tables for Partitioned Tables and also we don’t
need to specify the ‘ Location ‘ as we did for
external tables.
hive> create external table empPartitioned
(ID int, name string, location string, year
string)
Partitioned by (year string)
Row format delimited
Lines terminated by’#’
Fields terminated by’n’
Stored as textfile;
Rupak Roy

6. Hive Query Language (HQL)
 HQL inherits the SQL i.e. Structured Query Language to query most of the
tables
Example 1:
Select upper(name), TotalSales/100 as Average
From transactionaldata;
This will give us two columns, one Name in capital letters and the second is the
Average;
Example 2:
Select name, sellingprice – costprice as Profit
Where year = 2010,
And sellingprice > 100
From transactiondata;
#this will give us the profit based on selling price which are more than $100 for
the year 2010
Rupak Roy

7. We can also use the casting CAST() function to
change the data type to another.
Example 3:
Select name, selling price, CAST( year as int)
from transactionaldata;
Example 4: select CONCAT(name, id),location
Where date= 2005
We can also perform all the SQL queries like inner
joins, outer joins in hive.
Rupak Roy

8. Hive in RC File
 We can save hive data in different formats. We are
already familiar with the text format (stored as text
file), json, csv, xml and so on. However text format is
more convenient when it comes to sharing data with
other applications but not very effective in terms of
storage.
 Sequential file is another type of format that stores
data effectively by using binary key value pairs but
the drawback is it saves a complete row as a single
binary value. So whenever we query for a single
column hive have to read the full row even if one
column is requested.
 Let’s understand this the help of an example.
Rupak Roy

9. Create table in sequential file
Create table emp
(ID int, name string, location string)
Row format delimited
Lines terminated by’#’
Fields terminated by’n’
Stored as SEQUENCEFILE;
------------------------------------------
Describe formatted emp;
Rupak Roy

10. Row Vs Column Storage
 Row Oriented Storage:
Row oriented is efficient when retrieving for all the
columns data. For example from 50 columns & rows
and it realizes that it only has to scan 2 rows.
But when it comes to read only few columns it
needs to read all the rows. Best suits for row data.
ID Name Location Year
11 Bob IN 2005
22 Fara SG 2005
Rupak Roy

11. Row Vs Column Storage
 Columns Oriented Storage: is the vice versa of
row oriented storage that is best suited when it
comes to reading few columns
ID Name Location Year
11 Bob IN 2005
22 Fara SG 2005
33 Niki JP 2005
44 Steve NZ 2005
Rupak Roy

12. Record Columnar File
 To address the issue of row oriented storage
RC(Record Columnar ) file format was created.
 Along with the hive, RC file format was also
developed by Facebook.
 RC file stores data on disk in a record columnar
way that splits rows horizontally into row groups.
Row Group 1 Row Group 2
ID Name Location Year
11 Bob IN 2005
22 Fara SG 2005
33 Niki Jp 2005
ID Name Location Year
44 Steve NZ 2005
55 Nina RU 2009
66 Ryan IN 2005
Rupak Roy

13. Create table empRC
( ID int, name sring, location string)
Stored as RCFile;
----------------
Describe formatted empRC;
-----------------
Load data in hive
Insert overwrite table empRC select * from emp;
-------------------
Now query the table empRC and emp to observe
the difference in time taken to process the request.
Rupak Roy

14. Next
 Apache Hbase a column oriented non-
relational distributed database
management system.
Rupak Roy

15.  Stay Tuned.
Rupak Roy