Storing query result in a variable

Question

I have a query whose result I wanted to store in a variable How can I do it ? I tried

./hive -e  "use telecom;insert overwrite local directory '/tmp/result' select
avg(a) from abc;"

./hive --hiveconf MY_VAR =`cat /tmp/result/000000_0`;

I am able to get average value in MY_VAR but it takes me in hive CLI which is not required and is there a way to access unix commands inside hive CLI?

Answer 1

Use Case: in mysql the following is valid:

set @max_date := select max(date) from some_table;
select * from some_other_table where date > @max_date;

This is super useful for scripts that need to repeatedly call this variable since you only need to execute the max date query once rather than every time the variable is called.

HIVE does not currently support this. (please correct me if I'm wrong! I have been trying to figure out how to do this all all afternoon)

My workaround is to store the required variable in a table that is small enough to map join onto the query in which it is used. Because the join is a map rather than a broadcast join it should not significantly hurt performance. For example:

drop table if exists var_table;

create table var_table as
select max(date) as max_date from some_table;

select some_other_table.*
from some_other_table
left join var_table
where some_other_table.date > var_table.max_date;

The suggested solution by @visakh is not optimal because stores the string 'select count(1) from table_name;' rather than the returned value and so will not be helpful in cases where you need to call a var repeatedly during a script.

Answer 2

Storing hive query output in a variable and using it in another query.

In shell create a variable with desired value by doing:

var=`hive -S -e "select max(datekey) from ....;"`
echo $var

Use the variable value in another hive query by:

hive -hiveconf MID_DATE=$var -f test.hql