Encoding in temp tables in RedShift - amazon-redshift

Question

I am using temp staging tables, TempStaging, for doing some merges. The data in some columns for main table, MainTable, is encoded in lzo, say C1. The merge output goes back into MainTable.
In order to ensure same dist key for TempStaging, I am creating it using create table. For some reasons I cannot use Create Table as.
So should I encode the column C1 in to lzo? Or leave it without encoding? Would RedShift short circuit the [decode while select from MainTable, encode while writing into TempStaging, decode while selecting from TempTable for merge, Encode back again while writing it into MainTable]
Because I am thinking that if that short circuiting is not happening, I am better of leaving the encoding, trading away some memory to CPU gains.
-Amit

Answer 1

Data in Redshift is always decoded when it's read from the table AFAIK. There are a few DBs that can operate directly on compressed data but Redshift does not.
There is no absolute rule on whether you should use encoding in a temp table. It depends on how much data is being written. I've found it's faster with encoding 90+% of the time so that's my default approach.
As you note, ensuring that the temp table uses the same dist key is No. 1 priority. You can specify the dist key (and column encoding) in a CREATE TABLE AS though:
CREATE TABLE my_new_table
DISTKEY(my_dist_key_col)
AS
SELECT *
FROM my_old_table
;