Convert positive data into negetive data (entire column) in Postgres Server

Question

The current data in my table is:

  a   b
---------  
 -1   5
 -11  2   
 -5  32

My request is to convert every data of column a into negative value.

But how to update the positive values into the negative selecting the entire column?

Answer 1

Try this:

 Update table set a= 0-a where a >0

Answer 2

UPDATE mytable SET a = a * -1;

This multiplies all values in 'a' by -1. Now, if the value is already negative, it will become positive. You you want to make sure they are always negative, do this:

UPDATE mytable SET a = a * -1 WHERE a > 0;