Don't. It's a PITA to use, and though it's simple to insert the values to start with, it rapidly descends into nastiness.
Instead, have a "linking" table:
ID Name Dept Sal
1 Abc Mech 20000
ID DeptId TechId
1 1 1
2 1 2
3 1 3
You then use a JOIN to combine information when you want to retrieve it.
SELECT d.*, t.TechName FROM Depts d
JOIN DeptTech dt ON d.ID = dt.DeptId
JOIN Techs t ON d.TechID = t.ID
That way, adding and removing techs is a trivial job: just delete the linking row.