LOOP JOIN
Applies to ❌ Open Source Edition ✅ Express Edition ✅ Professional Edition ✅ Enterprise Edition
The LOOP JOIN (or nested loop join) algorithm runs a nested loop to fetch all rows of the second table corresponding to the rows of the first table. This typically has a higher algorithmic complexity than a linear one, which is why it can be a slower choice for larger data sets, although it's a good choice for small data sets - especially when indexes are available for nested loop lookups. An example:
SELECT * FROM AUTHOR INNER LOOP JOIN BOOK ON BOOK.AUTHOR_ID = AUTHOR.ID
create.select()
.from(AUTHOR)
.loopJoin(BOOK)
.on(BOOK.AUTHOR_ID.eq(AUTHOR.ID))
.fetch();
Dialect support
This example using jOOQ:
selectFrom(AUTHOR.loopJoin(BOOK).on(BOOK.AUTHOR_ID.eq(AUTHOR.ID)))
Translates to the following dialect specific expressions:
CockroachDB
SELECT
AUTHOR.ID,
AUTHOR.FIRST_NAME,
AUTHOR.LAST_NAME,
AUTHOR.DATE_OF_BIRTH,
AUTHOR.YEAR_OF_BIRTH,
AUTHOR.DISTINGUISHED,
BOOK.ID,
BOOK.AUTHOR_ID,
BOOK.TITLE,
BOOK.PUBLISHED_IN,
BOOK.LANGUAGE_ID
FROM AUTHOR
INNER LOOKUP JOIN BOOK
ON BOOK.AUTHOR_ID = AUTHOR.ID
Oracle
SELECT /*+leading(AUTHOR BOOK) use_nl(AUTHOR BOOK)*/
AUTHOR.ID,
AUTHOR.FIRST_NAME,
AUTHOR.LAST_NAME,
AUTHOR.DATE_OF_BIRTH,
AUTHOR.YEAR_OF_BIRTH,
AUTHOR.DISTINGUISHED,
BOOK.ID,
BOOK.AUTHOR_ID,
BOOK.TITLE,
BOOK.PUBLISHED_IN,
BOOK.LANGUAGE_ID
FROM AUTHOR
JOIN BOOK
ON BOOK.AUTHOR_ID = AUTHOR.ID
SQLServer
SELECT
AUTHOR.ID,
AUTHOR.FIRST_NAME,
AUTHOR.LAST_NAME,
AUTHOR.DATE_OF_BIRTH,
AUTHOR.YEAR_OF_BIRTH,
AUTHOR.DISTINGUISHED,
BOOK.ID,
BOOK.AUTHOR_ID,
BOOK.TITLE,
BOOK.PUBLISHED_IN,
BOOK.LANGUAGE_ID
FROM AUTHOR
INNER LOOP JOIN BOOK
ON BOOK.AUTHOR_ID = AUTHOR.ID
YugabyteDB
SELECT /*+leading(AUTHOR BOOK) NestLoop(AUTHOR BOOK)*/
AUTHOR.ID,
AUTHOR.FIRST_NAME,
AUTHOR.LAST_NAME,
AUTHOR.DATE_OF_BIRTH,
AUTHOR.YEAR_OF_BIRTH,
AUTHOR.DISTINGUISHED,
BOOK.ID,
BOOK.AUTHOR_ID,
BOOK.TITLE,
BOOK.PUBLISHED_IN,
BOOK.LANGUAGE_ID
FROM AUTHOR
JOIN BOOK
ON BOOK.AUTHOR_ID = AUTHOR.ID
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/* UNSUPPORTED */
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