How to fill a table cell with the data of another cell?

Question

PostgreSQL

there is a postgers table

in the 4th column (where there are asterisks), if the line in column No. 3 is equal to “minus”, write data = column02 of this line - column02 of the next line ( c = ab)
How to do it

Answer 1

Wrote a script on nodejs, went through a loop and everything is ok

Answer 2

In SQL Server, this is done using the LEAD () window function, PostgreSQL seems to have this too :

UPDATE table_name SET column4 = CASE
                             when column4 = 'minus' then column2 - lead(column2) OVER (ORDER BY id)
                             else column4
                           END

Answer 3

UPDATE blabla SET column4 = column1 - column2 WHERE column3...

Answer 4

I would dig in the direction of the Cursors. I can’t sketch out the code right off the bat, but bypassing the cursor involves sequential processing of each line, and there, in theory, you can do what you want.