Update query for 2 lakhs records

Question

I have 2 tables with 3 common columns (Col1, col2,Primary). One common column name is primary (oracle key word). No indexes are used on these tables. I need to write an update query as shown below. 
Emp table
Col1       col2        primay
100         101         y
103         104         n
201         105         y
100         101         y
Dept table
Col1       col2        primay
100         101         null
103         104         null
000         656         null
Update query Result
Col1       col2        primary
100         101         y
103         104         n
Please help me.
Thanks

Answer 1

Update dept d
set d.primay = (select distinct e.primay from emp e where e.col1 = d.col1 and e.col2 = d.col2);
In emp table there are 100 and 101 with two entries but with same primay value. so to handle such scenarios I have taken distinct iniside select statement.
if you have a case like where in emp table col1 and col2 are same and having different primay table, then obviously you should tell which value should go and update the dept table and based on what logic.