ERROR: column "int4" specified more than once - postgresql

Question

Steps for Execution:
Table Creation
CREATE TABLE xyz.table_a(
id bigint NOT NULL,
scores jsonb,
CONSTRAINT table_a_pkey PRIMARY KEY (id)
);
Add some dummy data :
INSERT INTO xyz.table_a(
id, scores)
VALUES (1, '{"a":20,"b":20}');
Function Creation
CREATE OR REPLACE FUNCTION xyz.example(
table_name text,
regular_columns text,
json_column text,
view_name text
) RETURNS text
LANGUAGE 'plpgsql'
COST 100
VOLATILE
AS $BODY$
DECLARE
cols TEXT;
cols_sum TEXT;
BEGIN
EXECUTE
format(
$ex$SELECT string_agg(
format(
'CAST(%2$s->>%%1$L AS INTEGER)',
key),
', '
)
FROM (SELECT DISTINCT key
FROM %1$s, jsonb_each(%2$s)
ORDER BY 1
) s;$ex$,
table_name, json_column
)
INTO cols;
EXECUTE
format(
$ex$SELECT string_agg(
format(
'CAST(%2$s->>%%1$L AS INTEGER)',
key
),
'+'
)
FROM (SELECT DISTINCT key
FROM %1$s, jsonb_each(%2$s)
ORDER BY 1) s;$ex$,
table_name, json_column
)
INTO cols_sum;
EXECUTE
format(
$ex$DROP VIEW IF EXISTS %2$s;
CREATE VIEW %2$s AS
SELECT %3$s, %4$s, SUM(%5$s) AS total
FROM %1$s
GROUP BY %3$s$ex$,
table_name, view_name, regular_columns, cols, cols_sum
);
RETURN cols;
END
$BODY$:
Call Function
SELECT xyz.example(
'xyz.table_a',
' id',
'scores',
'xyz.view_table_a'
);
Once you run these steps, I am getting an error
ERROR: column "int4" specified more than once
CONTEXT: SQL statement "
DROP VIEW IF EXISTS xyz.view_table_a;
CREATE VIEW xyz.view_table_a AS
SELECT id, CAST(scores->>'a' AS INTEGER), CAST(scores->>'b' AS INTEGER), SUM(CAST(scores->>'a' AS INTEGER)+CAST(scores->>'b' AS INTEGER)) AS total FROM xyz.table_a GROUP BY id

Answer 1

Look at the error message closely:
...
SELECT id, CAST(scores->>'a' AS INTEGER), CAST(scores->>'b' AS INTEGER),
...
There are multiple expressions without column alias. A named column like "id" defaults to the given name. But other expressions default to the internal type name, which is "int4" for integer. One might assume that the JSON key name is used, but that's not so. CAST(scores->>'a' AS INTEGER) is just another expression returning an unnamed integer value.
This still works for a plain SELECT. Postgres tolerates duplicate column names in the (outer) SELECT list. But a VIEW cannot be created that way. Would result in ambiguities.
Either add column aliases to expressions in the SELECT list:
SELECT id, CAST(scores->>'a' AS INTEGER) AS a, CAST(scores->>'b' AS INTEGER) AS b, ...
Or add a list of column names to CREATE VIEW:
CREATE VIEW xyz.view_table_a(id, a, b, ...) AS ...
Something like this should fix your function (preserving literal spelling of JSON key names:
...
format(
'CAST(%2$s->>%%1$L AS INTEGER) AS %%1$I',
key),
...
See the working demo here:
db<>fiddle here
Aside, your nested format() calls make the code pretty hard to read and maintain.