How to transpose or convert columns to rows in Hive?

Let’s say we have a table name  employee_multiple_depts and each employee in the table is mapped to 3 departments – dept1, dept2 and dept3.

select * from employee_multiple_depts;
+--------------------------------+--------------------------------+--------------------------------+--------------------------------+--+
| employee_multiple_depts.ename  | employee_multiple_depts.dept1  | employee_multiple_depts.dept2  | employee_multiple_depts.dept3  |
+--------------------------------+--------------------------------+--------------------------------+--------------------------------+--+
| Jerry                          | 10                             | 20                             | 30                             |
| Tom                            | 60                             | 70                             | 80                             |
+--------------------------------+--------------------------------+--------------------------------+--------------------------------+--+

What we need is to transpose or convert each department into a row for each employee.

Solution

We will first create an array with dept1, dept2 and dept3. We then explode the array. explode is an User Defined Table generating function (UDTF) which converts a row into multiple rows.

Finally we use LATERAL VIEW. LATERAL VIEW joins resulting output exploded rows to the input rows from employee_multiple_depts providing the below output.

Check out this post if you need more information on LATERAL VIEW

SELECT ename, dept
FROM employee_multiple_depts 
LATERAL VIEW explode(array(dept1, dept2, dept3)) dept_exp as dept;

+--------+-------+--+
| ename  | dept  |
+--------+-------+--+
| Jerry  | 10    |
| Jerry  | 20    |
| Jerry  | 30    |
| Tom    | 60    |
| Tom    | 70    |
| Tom    | 80    |
+--------+-------+--+
6 rows selected (0.164 seconds)