Fetch data from SQL db and display those data in Jira dropdown by the groovy script.

[RAJ SHANKAR SINGH]

Assume, I have multiple projects listed in JIRA where different people are working on different project. If I select some person lets assume A is that person then next drop-down auto-populated with all the project where A is working. how should I write this in the groovy script. 

[Nic Brough -Adaptavist-]

You don't.  You will need to write a new custom field to pull that data out of Jira and use it in a field.

You should really start by defining the need - what do the users gain from this?  And then you'll need to define "working on" and how that is represented by your Jira setup.