Unable to use lateral join

[Stefan Sator]

Hello Lukas,

how do I write this query correctly?

Wanted:

SELECT o.name, l.comment
FROM customerobjectdb_object AS o,
LATERAL (SELECT * FROM customerobjectdb_history AS h WHERE h.object_id = o.id
order by h.major_version desc, h.minor_version desc limit 1
) AS l
ORDER BY o.id;

Jooq(not correct)

var fetch = db.select(o.NAME,
//o.STATUS.convertFrom(x -> ObjectSafetyStatus.from(x)),
//o.CHANGED_AT,
//o.VERSION,
lateral(DSL.select(h.COMMENT)
.from(h)
.where(h.OBJECT_ID.eq(o.ID))
.orderBy(h.MAJOR_VERSION.desc(),
h.MINOR_VERSION.desc())
.limit(1)).as("l")
)
.from(o)
.orderBy(o.CHANGED_AT.desc())
.limit(10)
.fetch();

SQL

select "o"."name", row ("l"."comment") as "l"
from "public"."customerobjectdb_object" as "o"
order by "o"."changed_at" desc fetch next ? rows only

[Lukas Eder]

Why put your LATERAL derived table in SELECT with jOOQ, when you don't do that with SQL?

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[Stefan Sator]

Because I get sometimes confused.

I figured that out aswell just now before reading your comment :-)

But how do I select only some of the columns from the lateral join?

var fetch = db.select()
.from(o,

lateral(DSL.select(h.COMMENT)
.from(h)
.where(h.OBJECT_ID.eq(o.ID))
.orderBy(h.MAJOR_VERSION.desc(),
h.MINOR_VERSION.desc())
.limit(1)).as("l")
)

.orderBy(o.CHANGED_AT.desc())
.limit(10)
.fetch();

[Lukas Eder]

See: https://www.jooq.org/doc/latest/manual/sql-building/column-expressions/table-columns/dereferenced-table-columns/

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[Stefan Sator]

This works, but it doesnt look elegant.

Is there a better way?

CustomerobjectdbObject o = CustomerobjectdbObject.CUSTOMEROBJECTDB_OBJECT.as("o");
CustomerobjectdbHistory h = CustomerobjectdbHistory.CUSTOMEROBJECTDB_HISTORY.as("h");
CustomerobjectdbHistory l = CustomerobjectdbHistory.CUSTOMEROBJECTDB_HISTORY.as("l");

//@formatter:off
var fetch = db.select(o.NAME, l.field("comment"))

.from(o,
lateral(DSL.select(h.COMMENT)
.from(h)
.where(h.OBJECT_ID.eq(o.ID))
.orderBy(h.MAJOR_VERSION.desc(),
h.MINOR_VERSION.desc())
.limit(1)).as("l")
)
.orderBy(o.CHANGED_AT.desc())
.limit(10)
.fetch();

[Stefan Sator]

Final solution:

CustomerobjectdbObject o = CustomerobjectdbObject.CUSTOMEROBJECTDB_OBJECT.as("o");
CustomerobjectdbHistory h = CustomerobjectdbHistory.CUSTOMEROBJECTDB_HISTORY.as("h");
CustomerobjectdbHistory l = CustomerobjectdbHistory.CUSTOMEROBJECTDB_HISTORY.as("l");

//@formatter:off
var fetch = db.select(o.NAME, l.field("comment"))
.from(o,
lateral(DSL.select(h.COMMENT)
.from(h)
.where(h.OBJECT_ID.eq(o.ID))
.orderBy(h.MAJOR_VERSION.desc(),
h.MINOR_VERSION.desc())
.limit(1)).as(l)
)
.orderBy(o.CHANGED_AT.desc())
.limit(10)
.fetch();

[Stefan Sator]

And even better:

CustomerobjectdbObject o = CustomerobjectdbObject.CUSTOMEROBJECTDB_OBJECT.as("o");
CustomerobjectdbHistory h = CustomerobjectdbHistory.CUSTOMEROBJECTDB_HISTORY.as("h");
CustomerobjectdbHistory l = CustomerobjectdbHistory.CUSTOMEROBJECTDB_HISTORY.as("l");

//@formatter:off

var fetch = db.select(o.NAME, l.COMMENT)

.from(o,
lateral(DSL.select(h.COMMENT)
.from(h)
.where(h.OBJECT_ID.eq(o.ID))
.orderBy(h.MAJOR_VERSION.desc(),
h.MINOR_VERSION.desc())
.limit(1)).as(l)
)
.orderBy(o.CHANGED_AT.desc())
.limit(10)
.fetch();

[Stefan Sator]

Hi Lukas,

I dont get it to work for just some fields of the lateral join.

How do I do this?

public List<HomeShopTableUIModel> getShopPage() {
ShopdbObject o = ShopdbObject.SHOPDB_OBJECT;
ShopdbHistorie h = ShopdbHistorie.SHOPDB_HISTORIE;
ShopdbHistorie l = ShopdbHistorie.SHOPDB_HISTORIE;

Condition c = getTenantCondition(o);

//@formatter:off
var fetch = db.select(o.NAME)

.from(o,
lateral(DSL.select(h.COMMENT)
.from(h)
.where(h.OBJECT_ID.eq(o.ID))
.orderBy(h.MAJOR_VERSION.desc(),
h.MINOR_VERSION.desc())
.limit(1)).as("l")
)

.where(c)
.orderBy(o.CHANGED_AT.desc())
.limit(10)
.fetch();
//@formatter:on

[Lukas Eder]

Stefan,

What is your specific question? What have you tried? What didn't work?

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[Stefan Sator]

After lots of try and error this works, but is it the "correct" way?

CustomerobjectdbObject o = CustomerobjectdbObject.CUSTOMEROBJECTDB_OBJECT.as("o");
CustomerobjectdbHistory h = CustomerobjectdbHistory.CUSTOMEROBJECTDB_HISTORY.as("h");
CustomerobjectdbHistory l = CustomerobjectdbHistory.CUSTOMEROBJECTDB_HISTORY.as("l");

Condition c = getTenantCondition(o);

//@formatter:off

var fetch = db.select(o.NAME,
o.STATUS.convertFrom(x -> ObjectSafetyStatus.from(x)),
o.CHANGED_AT,
l.MAJOR_VERSION,
l.MINOR_VERSION,
l.COMMENT)
.from(o,
lateral(DSL.select(h.MAJOR_VERSION,
h.MINOR_VERSION,

h.COMMENT)
.from(h)
.where(h.OBJECT_ID.eq(o.ID))
.orderBy(h.MAJOR_VERSION.desc(),
h.MINOR_VERSION.desc())
.limit(1)).as(l)
)

.where(c)
.orderBy(o.CHANGED_AT.desc())
.limit(10)
.fetch(mapping((r1, r2, r3, r4, r5, r6) -> new HomeObjectTableUIModel(r1, r2, r3, r4, r5, r6)));
//@formatter:on

return fetch;

[Lukas Eder]

Let me rephrase my previous question:

What is your specific question? Why do you have doubts? What kind of answer are you expecting?

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[Stefan Sator]

At first I was unsure it there really is not other way to write:

CustomerobjectdbHistory h = CustomerobjectdbHistory.CUSTOMEROBJECTDB_HISTORY.as("h");
CustomerobjectdbHistory l = CustomerobjectdbHistory.CUSTOMEROBJECTDB_HISTORY.as("l");

But now I think it makes sense and is the only way to get both type safety and to be able to rename a table at the same time.

[Lukas Eder]

You probably mean the declaration of aliased tables up front, instead of embedded in the query, like in SQL? There's no other way to declare variables in Java. Java can't follow SQL's syntax where stuff is referenced before it is declared (lexically).

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[Stefan Sator]

Thanks Lukas!