Using LAG and comparing the column - sql

Question

I am joining two tables together using a lag function so that the first table will display no duplicate metric rows.
I am however having trouble referencing the lagged column when pre selecting for a join.
My query is as follows, the mentioned column is marked with !!!
select "Campaign",
"Ad group" ,
"Final URL" ,
"Headline 1" ,
"Headline 2" ,
"Description" ,
"Path 1" ,
"Path 2" ,
"Status" ,
"Labels" ,
case when prev_key is null or prev_key != "Key" then "Clicks" end as
"Clicks",
case when prev_key is null or prev_key != "Key" then "Impressions" end
as
"Impressions",
case when prev_key is null or prev_key != "Key" then "Cost" end as
"Cost",
case when prev_key is null or prev_key != "Key" then "Avg. position" end
as
"Avg. position",
case when prev_key is null or prev_key != "Key" then "Initial Leads" end
as
"Initial Leads",
case when prev_key is null or prev_key != "Key" then "Evaluations" end
as
"Evaluations",
case when prev_key is null or prev_key != "Key" then "Won Leads" end as
"Won Leads",
case when prev_key is null or prev_key != "Key" then "Opportunities" end
as
"Opportunities",
"Language",
"Network",
"Main Keyword",
"Cluster Keyword 1",
"Match Type"
from
(SELECT
"x"."Campaign",
"x"."Ad group",
"x"."Final URL",
"x"."Headline 1",
"x"."Headline 2",
"x"."Description",
"x"."Path 1",
"x"."Path 2",
"x"."Status",
"x"."Labels",
!!!lag ("x"."Key") over () AS prev_Key!!!,
"x"."Clicks",
"x"."Impressions",
"x"."Cost",
"x"."Avg. position",
"x"."Initial Leads",
"x"."Evaluations",
"x"."Won Leads",
"x"."Opportunities",
"x"."Language",
"x"."Network",
"x"."Main Keyword",
"x"."Cluster Keyword 1",
"x"."Match Type"
FROM ad_copies_final_joined_concatenated x join
ad_copies_final_to_join_concatenated
using ("Key")
order by "Campaign" desc, "Key"
) sub ;
The output error message is as follows;
ERROR: column "Key" does not exist
LINE 11: case when prev_key is null or prev_key != "Key" then "Cli...
^

Answer 1

You shouldn't use the same syntax for string, and column names.
I suspect the error is due to the use of double quotations with strings.
Try changing everything that is not a column to a single quote mark .
E.G.
case when prev_key is null or prev_key != 'Key' then "Avg. position" end
as "Avg. position"
Or, you actually want to compare prev_key column with Key column. In this case, you forgot to select Key in your inner query, so add it to the select list.