How do I use concat and case switch together in PostgresSQL? - sql

Question

I am trying to use concat as function and inside the same function use case switch statements in PostgresSQL. The end goal is populating a table with a bunch of statements that change according to the case.
Does anybody know how to solve this?
I tried to use '+' and ',' but I always get the same Syntax error
(SELECT concat(cast(idpersonale as varchar(5)),' = '
,case when dstitolo is not null then dstitolo else '' end + ' '
,case when dsnome is not null then dsnome else '' end + ' '
,case when dscognome is not null then dscognome else '' end
dscognome)
FROM global.glb_personale
WHERE cch.glb_personale.idpersonale =inter.interventoeseguitoda) as InterventoEseguitoDa
FROM cch.pats_cch_interventi inter
WHERE (idtiporecord is null or not idtiporecord in('uti','int')) and
NOT idintervento IN (SELECT idint
FROM cch.glo_error_data_2
WHERE (iddb = 'cch') AND (cnerror = 1))
order by idintervento;

Answer 1

Concatenation works with || operator or concat(text1, text2, text3, ...) function. Every text literal can be also an expression which gives a type text, like a CASE clause:
demo:db<>fiddle
SELECT
'you' || 'can' || 'concat' || 'like' || 'that' AS concat1,
concat('or', 'like', 'that') AS concat2,
concat('Mix' || 'both', 'up') AS concat3,
concat(
'And',
CASE WHEN false THEN 'now' ELSE 'doint' END || 'this',
CASE
WHEN true THEN 'with' || 'some'
WHEN false THEN 'CASE'
ELSE 'clauses'
END
) AS concat4
That means in your case: Change concat(text1 + text2 + text3) to concat(text1, text2, text3) (because the texts are function arguments) or to text1 || text2 || text3

Answer 2

since you are using concat(), replace + to , instead.
(SELECT concat(cast(idpersonale as varchar(5)),' = '
,case when dstitolo is not null then dstitolo else '' end, ' '
,case when dsnome is not null then dsnome else '' end, ' '
,case when dscognome is not null then dscognome else '' end
dscognome)
FROM global.glb_personale
WHERE cch.glb_personale.idpersonale =inter.interventoeseguitoda) as InterventoEseguitoDa
FROM cch.pats_cch_interventi inter
WHERE (idtiporecord is null or not idtiporecord in('uti','int')) and
NOT idintervento IN (SELECT idint
FROM cch.glo_error_data_2
WHERE (iddb = 'cch') AND (cnerror = 1))

Answer 3

While the concatenation operator (||) and the function (concat) combine strings there is a big difference between them: how they handle nulls.
If any operand is null then the concatenation operator result is NULL.
If any operand is null then the concatenation function moves to the next operand, leaving previous and subsequent results as they would had the null operand not been present. Example:
with dscognome (idpersonale,dstitolo ,dsnome ,dscognome) as
( values (1,'a','b','c')
, (2,'d','e',null)
, (3,'f',null,'g')
, (4,null, 'h', 'i')
, (5,null, null, null)
)
select idpersonale
, dstitolo || dsnome || dscognome "using || opreator"
, concat(dstitolo,dsnome,dscognome) "using concat function"
from dscognome;
Since the entire purpose of the case structure is to handle nulls, using the concatenation function entirely negates it's requirement and the query can be written:
with dscognome (idpersonale,dstitolo ,dsnome ,dscognome) as
( values (1,'a','b','c')
, (2,'d','e',null)
, (3,'f',null,'g')
, (4,null, 'h', 'i')
, (5,null, null, null)
)
SELECT concat(cast(idpersonale as varchar),' = '
, dstitolo , ' '
, dsnome, ' '
, dscognome )
from dscognome;