RedShift - update table with date from a timestamp column

Question

I have a table named adata in redshift which contains a column timestamp with integer type data variable. The timestamp column holds the timestamp as epoch values. I have added a new column called rdate with date variable type. I am trying to insert date value into rdate column by converting the timestamp column.

What is working;

select timestamp 'epoch' + timestamp * interval '1 second' AS rdate from adata;

This prints the rdate column with timestamp as date and time nicely.

what is not working

insert into adata (rdate) select timestamp 'epoch' + timestamp * interval '1 second' AS rdate from adata;

I tried with an update statement:

update adata set rdate = (select timestamp 'epoch' + timestamp * interval '1 second' AS rdate from adata);


ts              rdate
1611306839      need date here
1611469226      need date here
1611399334      need date here
1611373685      need date here

another option which I tried:

update adata set rdate = (select (timestamp 'epoch' + timestamp * interval '1 second') AS rdate from adata);

Answer 1

It appears that you want to update existing rows in a table . In that case, you would use an UPDATE command.

Since the rows will be updated based upon the value of other columns in the same table, you could simply use:

UPDATE adata SET rdate = timestamp 'epoch' + timestamp * interval '1 second'

where timestamp is the column that contains the existing value.

(Using INSERT would add additional rows, which probably isn't what you are seeking.)