How to improve the insertion time

How to improve the insertion time

 

  

Hello all,

I have the following script

Insert into ZZ
Select a.*, b.*
From XX a, YY b
Where a.xx=b.xx

Table XX and YY contains about 1.2M records
Running this script takes about 3hours.
Can any body advice me on what to do to improve/reduce the execution
time.
Thank you.

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