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I stumbled upon a really fascinating query on Stack Overflow about learn how to use jOOQ’s MULTISET operator to nest a group, after which filter the consequence by whether or not that nested assortment incorporates a price.
The query is jOOQ particular, however think about, you’ve got a question that nests collections utilizing JSON in PostgreSQL. Assuming, as all the time, the Sakila database. Now, PostgreSQL doesn’t assist the SQL customary MULTISET operator, however we will use ARRAY, which works nearly the identical manner.
SELECT
f.title,
ARRAY(
SELECT ROW(
a.actor_id,
a.first_name,
a.last_name
)
FROM actor AS a
JOIN film_actor AS fa USING (actor_id)
WHERE fa.film_id = f.film_id
ORDER BY a.actor_id
)
FROM movie AS f
ORDER BY f.title
This produces all movies and their actors as follows (I’ve truncated the arrays for readability functions. You get the purpose):
title |array
---------------------------+--------------------------------------------------------------------------------------
ACADEMY DINOSAUR |{"(1,PENELOPE,GUINESS)","(10,CHRISTIAN,GABLE)","(20,LUCILLE,TRACY)","(30,SANDRA,PECK)"
ACE GOLDFINGER |{"(19,BOB,FAWCETT)","(85,MINNIE,ZELLWEGER)","(90,SEAN,GUINESS)","(160,CHRIS,DEPP)"}
ADAPTATION HOLES |{"(2,NICK,WAHLBERG)","(19,BOB,FAWCETT)","(24,CAMERON,STREEP)","(64,RAY,JOHANSSON)","(1
AFFAIR PREJUDICE |{"(41,JODIE,DEGENERES)","(81,SCARLETT,DAMON)","(88,KENNETH,PESCI)","(147,FAY,WINSLET)"
AFRICAN EGG |{"(51,GARY,PHOENIX)","(59,DUSTIN,TAUTOU)","(103,MATTHEW,LEIGH)","(181,MATTHEW,CARREY)"
AGENT TRUMAN |{"(21,KIRSTEN,PALTROW)","(23,SANDRA,KILMER)","(62,JAYNE,NEESON)","(108,WARREN,NOLTE)",
AIRPLANE SIERRA |{"(99,JIM,MOSTEL)","(133,RICHARD,PENN)","(162,OPRAH,KILMER)","(170,MENA,HOPPER)","(185
AIRPORT POLLOCK |{"(55,FAY,KILMER)","(96,GENE,WILLIS)","(110,SUSAN,DAVIS)","(138,LUCILLE,DEE)"}
ALABAMA DEVIL |{"(10,CHRISTIAN,GABLE)","(22,ELVIS,MARX)","(26,RIP,CRAWFORD)","(53,MENA,TEMPLE)","(68,
Now, the query on Stack Overflow was, learn how to filter this consequence by whether or not the ARRAY (or MULTISET) incorporates a selected worth.
Filtering the ARRAY
We are able to’t simply add a WHERE clause to the question. Due to the logical order of operations in SQL, the WHERE clause “occurs earlier than” the SELECT clause, so the ARRAY isn’t but out there to WHERE. We may, nonetheless, wrap all the pieces in a derived desk and do that, as a substitute:
SELECT *
FROM (
SELECT
f.title,
ARRAY(
SELECT ROW(
a.actor_id,
a.first_name,
a.last_name
)
FROM actor AS a
JOIN film_actor AS fa USING (actor_id)
WHERE fa.film_id = f.film_id
ORDER BY a.actor_id
) AS actors
FROM movie AS f
) AS f
WHERE actors @> ARRAY[(
SELECT ROW(a.actor_id, a.first_name, a.last_name)
FROM actor AS a
WHERE a.actor_id = 1
)]
ORDER BY f.title
Excuse the unwieldy ARRAY @> ARRAY operator. I’m not conscious of a greater method right here, as a result of it’s laborious to unnest a structurally typed RECORD[] array in PostgreSQL, if we don’t use a nominal sort (CREATE TYPE ...). If you recognize a greater technique to filter, please let me know within the feedback part. Right here’s a greater model:
SELECT *
FROM (
SELECT
f.title,
ARRAY(
SELECT ROW(
a.actor_id,
a.first_name,
a.last_name
)
FROM actor AS a
JOIN film_actor AS fa USING (actor_id)
WHERE fa.film_id = f.film_id
ORDER BY a.actor_id
) AS actors
FROM movie AS f
) AS f
WHERE EXISTS (
SELECT 1
FROM unnest(actors) AS t (a bigint, b textual content, c textual content)
WHERE a = 1
)
ORDER BY f.title
Anyway, this produces the specified consequence:
title |actors
---------------------+-------------------------------------------------------------------------------------------------
ACADEMY DINOSAUR |{"(1,PENELOPE,GUINESS)","(10,CHRISTIAN,GABLE)","(20,LUCILLE,TRACY)","(30,SANDRA,PECK)","(40,JOHNN
ANACONDA CONFESSIONS |{"(1,PENELOPE,GUINESS)","(4,JENNIFER,DAVIS)","(22,ELVIS,MARX)","(150,JAYNE,NOLTE)","(164,HUMPHREY
ANGELS LIFE |{"(1,PENELOPE,GUINESS)","(4,JENNIFER,DAVIS)","(7,GRACE,MOSTEL)","(47,JULIA,BARRYMORE)","(91,CHRIS
BULWORTH COMMANDMENTS|{"(1,PENELOPE,GUINESS)","(65,ANGELA,HUDSON)","(124,SCARLETT,BENING)","(173,ALAN,DREYFUSS)"}
CHEAPER CLYDE |{"(1,PENELOPE,GUINESS)","(20,LUCILLE,TRACY)"}
COLOR PHILADELPHIA |{"(1,PENELOPE,GUINESS)","(106,GROUCHO,DUNST)","(122,SALMA,NOLTE)","(129,DARYL,CRAWFORD)","(163,CH
ELEPHANT TROJAN |{"(1,PENELOPE,GUINESS)","(24,CAMERON,STREEP)","(37,VAL,BOLGER)","(107,GINA,DEGENERES)","(115,HARR
GLEAMING JAWBREAKER |{"(1,PENELOPE,GUINESS)","(66,MARY,TANDY)","(125,ALBERT,NOLTE)","(143,RIVER,DEAN)","(155,IAN,TANDY
Now, all the outcomes are assured to be movies wherein 'PENELOPE GUINESS' was an ACTOR. However is there a greater resolution?
Utilizing ARRAY_AGG as a substitute
Nonetheless, in native PostgreSQL, it will be higher (on this case) to make use of ARRAY_AGG, I feel:
SELECT
f.title,
ARRAY_AGG(ROW(
a.actor_id,
a.first_name,
a.last_name
) ORDER BY a.actor_id) AS actors
FROM movie AS f
JOIN film_actor AS fa USING (film_id)
JOIN actor AS a USING (actor_id)
GROUP BY f.title
HAVING bool_or(true) FILTER (WHERE a.actor_id = 1)
ORDER BY f.title
This produces the very same consequence:
title |actors
---------------------+------------------------------------------------------------------------------------------------
ACADEMY DINOSAUR |{"(1,PENELOPE,GUINESS)","(10,CHRISTIAN,GABLE)","(20,LUCILLE,TRACY)","(30,SANDRA,PECK)","(40,JOHN
ANACONDA CONFESSIONS |{"(1,PENELOPE,GUINESS)","(4,JENNIFER,DAVIS)","(22,ELVIS,MARX)","(150,JAYNE,NOLTE)","(164,HUMPHRE
ANGELS LIFE |{"(1,PENELOPE,GUINESS)","(4,JENNIFER,DAVIS)","(7,GRACE,MOSTEL)","(47,JULIA,BARRYMORE)","(91,CHRI
BULWORTH COMMANDMENTS|{"(1,PENELOPE,GUINESS)","(65,ANGELA,HUDSON)","(124,SCARLETT,BENING)","(173,ALAN,DREYFUSS)"}
CHEAPER CLYDE |{"(1,PENELOPE,GUINESS)","(20,LUCILLE,TRACY)"}
COLOR PHILADELPHIA |{"(1,PENELOPE,GUINESS)","(106,GROUCHO,DUNST)","(122,SALMA,NOLTE)","(129,DARYL,CRAWFORD)","(163,C
ELEPHANT TROJAN |{"(1,PENELOPE,GUINESS)","(24,CAMERON,STREEP)","(37,VAL,BOLGER)","(107,GINA,DEGENERES)","(115,HAR
GLEAMING JAWBREAKER |{"(1,PENELOPE,GUINESS)","(66,MARY,TANDY)","(125,ALBERT,NOLTE)","(143,RIVER,DEAN)","(155,IAN,TAND
How does it work?
- We’re grouping by
FILMand combination the contents per movie right into a nested assortment. - We are able to now use
HAVINGto filter on teams. BOOL_OR(TRUE)isTRUEas quickly because theGROUPis non-emptyFILTER (WHERE a.actor_id = 1)was that filter standards, which we place within the group
So, the HAVING predicate is TRUE if there’s not less than one ACTOR_ID = 1, or NULL in any other case, which has the identical impact as FALSE. When you’re a purist, wrap the predicate in COALESCE(BOOL_OR(...), FALSE)
Intelligent or neat, or a little bit of each?
Doing this with jOOQ
Right here’s the jOOQ model, that works on any RDBMS that helps MULTISET_AGG (ARRAY_AGG emulation continues to be pending):
ctx.choose(
FILM_ACTOR.movie().TITLE,
multisetAgg(
FILM_ACTOR.actor().ACTOR_ID,
FILM_ACTOR.actor().FIRST_NAME,
FILM_ACTOR.actor().LAST_NAME))
.from(FILM_ACTOR)
.groupBy(FILM_ACTOR.movie().TITLE)
.having(boolOr(trueCondition())
.filterWhere(FILM_ACTOR.actor().ACTOR_ID.eq(1)))
.orderBy(FILM_ACTOR.movie().TITLE)
.fetch();
Whereas the highly effective MULTISET worth constructor will get many of the fame with jOOQ customers, let’s not overlook there’s additionally a barely much less highly effective, however often actually helpful MULTISET_AGG combination operate, which can be utilized for aggregations or as a window operate!
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