Multiple case in update postgres - postgresql

Question

I need to update 2 columns in table with same conditions. I know, that each of them would take a lot of time. How can I concatenate 2 updates into 1, which can be faster?
-- first update
update t1
set col1 =
case when cc1 is not NULL and cc1 <> 0 then 'A'
when cc2 is not NULL and cc2 <> 0 then 'B'
when cc3 is not NULL and cc3 <> 0 then 'C'
else null
end;
-- with same cond
update t1
set col2 =
case when cc1 is not NULL and cc1 <> 0 then 'qwe rty'
when cc2 is not NULL and cc2 <> 0 then 'qzaz wsx'
when cc3 is not NULL and cc3 <> 0 then 'zxcv asdf'
else 'pl ok'
end;
-- my effort to concatenate, dont work
update t1
set (col1, col2) =
(select c1, c2 from
(select case when t2.cc1 is not NULL and t2.cc1 <> 0 then 'A' as c1, 'qwe rty' as c2
when t2.cc2 is not NULL and t2.cc2 <> 0 then ('B', 'qaz wsx')
when t2.cc3 is not NULL and t2.cc3 <> 0 then ('C', ' zxcv asdf')
else (null, 'pl ok')
end
from t1 as t2 where t1.key_column1 = t2.key_column1 and t1.key_column2 = t2.key_column2 and t1.key_column3 = t2.key_column3) f)
;

Answer 1

This is the way I would do it.
WITH cte AS (SELECT * FROM
(VALUES(1, 'A', 'qwe rty'),(2, 'B', 'qaz wsx'),(3, 'C', 'zxcv asdf'),(4, NULL, 'pl ok')) v (id,c1,c2))
UPDATE so_demo
SET col1 = cte.c1, col2 = cte.c2
FROM cte WHERE cte.id = CASE WHEN COALESCE(cc1, 0) <> 0 THEN 1
WHEN COALESCE(cc2, 0) <> 0 THEN 2
WHEN COALESCE(cc3, 0) <> 0 THEN 3
ELSE 4 END;
By way of explanation, I have put the possible values into a cte assigning them an id in addition to the values. I can then put the case statement in the where clause generating the necessary id. Note the use of COALESCE to make the WHENs simpler to read.

Answer 2

One way is to use arrays.
UPDATE t1
SET (col1,
col2) = (SELECT x[1],
x[2]
FROM (SELECT CASE
WHEN cc1 IS NOT NULL
AND cc1 <> 0 THEN
ARRAY['A',
'qwe rty']
WHEN cc2 IS NOT NULL
AND cc2 <> 0 THEN
ARRAY['B',
'qzaz wsx']
...
ELSE
ARRAY[NULL,
'pl ok']
END) AS x
(x));
But in terms of runtime optimization the gain compared to just UPDATE ... SET col1 = CASE ..., col2 = CASE ... should be neglectable, if any.