Adding new columns to the table from other tables

Please push on the right decision, I’ve been fighting for the second day, I tried a lot, one of the most successful was the use of MERGE , but either I wrote crookedly or it didn’t work.

I need to create a temporary table with certain columns and attach one new column one by one (depending on certain tasks)

Below is the code I wrote for the sample. I tried to add a column from the table on the basis of which I created a temporary one. But there is an error

multi-part identifiear "tempTable.column_new"

one)

  select col1, col2, ACCOUNT_RC into #account from TABLE1 

2)

  alter table #account add ACCOUNT_RC_izmenen numeric(18,0) 

3)

  MERGE #account AS tempTable USING (SELECT ACCOUNT_RC + 1000000, ACCOUNT_RC from TABLE1) as source (ACCOUNT_RC_izmenen, ACCOUNT_RC) ON (tempTable.ACCOUNT_RC = source.ACCOUNT_RC) WHEN MATCHED THEN UPDATE SET tempTable.column_new = source.ACCOUNT_RC_izmenen ;