How to concatenate cols under special rules? - sql

Question

I want to select concatenated string, max 255 char. Original query, without shortenings, was:
SELECT
b.title
||
CASE
WHEN b.subtitle != '' THEN '. ' || b.subtitle
ELSE ''
END
||
CASE
WHEN b.cover = 'paperback' THEN ' P'
WHEN b.cover = 'hardcover' THEN ' K'
WHEN b.cover = 'spiral' THEN ' S'
ELSE ''
END
||
CASE
WHEN b.year > 0 THEN ' ' || b.year
ELSE ''
END
||
CASE
WHEN b.volume > 0 THEN ' ' || b.volume || '. osa'
ELSE ''
END
||
CASE
WHEN p.name != '' THEN ' ' || p.name
ELSE ''
END
AS name
FROM table b
JOIN table_p p
ON b.id = p.foreign_id;
Rule: concatenated string may be up to 255 chars
Prioritized fields:
b.title (text, up to 250 chars),
b.cover (2 chars),
b.year (4 char + space = 5),
b.volume (int<100 + additional string '. osa' = 7-8 chars).
Less important:
b.subtitle (text, up to 250 chars),
p.name (text, up to 150 chars )
All fields besides b.title may absent/be empty.
One approach I can think of: because three short mandatory fields (cover, year, volume) may be max 15 chars, everything other could be max 240 chars. Because p.name is not so important, I could concatenate and cut afterwards, if needed. So main objective with this approach: b.title + b.subtitle must fit into 240 chars. Looks like that:
SELECT
SUBSTR(
SUBSTR( b.title
||
CASE
WHEN b.subtitle != '' THEN '. ' || b.subtitle
ELSE ''
END,
0, 240 )
||
CASE
WHEN b.cover = 'paperback' THEN ' P'
WHEN b.cover = 'hardcover' THEN ' K'
WHEN b.cover = 'spiral' THEN ' S'
ELSE ''
END
||
CASE
WHEN b.year > 0 THEN ' ' || b.year
ELSE ''
END
||
CASE
WHEN b.volume > 0 THEN ' ' || b.volume || '. osa'
ELSE ''
END
||
CASE
WHEN p.name != '' THEN ' ' || p.name
ELSE ''
END,
0, 255 ) AS name
FROM table b
JOIN table_p p
ON b.id = p.foreign_id;
This approach is Ok-ish.
My question: is there better way to control every aspect of such concatenation?
I am using Postgresql 9.6