Automatic conversion of Oracle-style implicit joins to ANSI JOINs using jOOQ

虽然jOOQ主要被用作Javaembedded dynamicSQL的内部SQL DSL,It offers the best solution on the market,但jOOQIt is also increasingly being used for one of its secondary functions.在jOOQ 3.9中引入的解析器Mainly to be able to解析DDL语句,For example reverse engineering your schema for code generation purposes,We have added more and more features and SQL转换能力,Enables the parser as a standalone product,通过命令行界面、我们的网站or by ordinaryjOOQ API来使用. 在jOOQ 3.14中增加的一个功能,Mainly for those usejOOQUseful as a profiler,就是将旧的OracleStyle implicit joins are converted to ANSI JOIN的能力.

为什么要避免 "隐式连接"？

大多数RDBMSVendors all support the old onesOraclestyle implicit join syntax,and optimized appropriately.在过去,在SQL-92之前,This is what we use to internally join tables,例如,在查询Sakila数据库时.

SELECT *
FROM actor a, film_actor fa, film f
WHERE a.actor_id = fa.actor_id
AND fa.film_id = f.film_id


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诚然,This syntax is very intuitive.Just declare all the tables you want to get data from,Then make sure to only filter by matching primary keys/foreign key values ​​to hold the appropriate data. 当然,This can go horribly wrong.For many obvious reasons,例如,When you forget a join predicate after adding a table.If the query is complex,This can be hard to debug.解决方案是ANSI JOIN.从SQL-92开始（差不多30年了！）,That's what we are in mostRDBMSconnection in .

SELECT *
FROM actor a
JOIN film_actor fa ON a.actor_id = fa.actor_id
JOIN film f ON fa.film_id = f.film_id


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Although it is still possible to define the wrong join predicate,But at least it is no longer possible to forget a predicate,Because this is grammatically incorrect（除了MySQL,遗憾的是,在那里,ON子句是可选的）.

SELECT *
FROM actor a
JOIN film_actor fa -- Syntax error
JOIN film f -- Syntax error


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jOOQ的隐式JOIN

注意,People usually refer to the above syntax as "隐式连接",而JPQL和jOOQAnother one was recycled"隐式连接 "的术语,It is based on foreign key paths,甚至比ANSI SQLThe syntax is less error-prone.使用jOOQ,The above query can be written as follows.

ctx.select(
FILM_ACTOR.actor().asterisk(),
FILM_ACTOR.asterisk(),
FILM_ACTOR.film().asterisk())
.from(FILM_ACTOR)
.fetch();


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These exist only in the queryto-one的关系路径,will be implicitly appropriateLEFT JOIN 或INNER JOIN 添加到FROM 子句中.It's just normalANSI JOIN之上的便利,而不是替代.

改造Oracle的隐式连接

When you have an old codebase,You want to upgrade and convert all queries to useANSI JOIN时,请使用jOOQ来实现.你可以使用jOOQ的编程功能（如前所述）,or free websitewww.jooq.org/translate.在网站上,只需选择 "Oracle风格到ANSI JOIN "选项,Place the following on the leftSQL：输入

SELECT
a.first_name,
a.last_name,
count(c.category_id)
FROM
actor a,
film_actor fa,
film f,
film_category fc,
category c
WHERE a.actor_id = fa.actor_id
AND fa.film_id = f.film_id
AND fc.category_id = c.category_id
GROUP BY
a.actor_id,
a.first_name,
a.last_name


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输出

SELECT
a.first_name,
a.last_name,
count(c.category_id)
FROM actor a
JOIN film_actor fa
ON a.actor_id = fa.actor_id
JOIN film f
ON fa.film_id = f.film_id
CROSS JOIN (
film_category fc
JOIN category c
ON fc.category_id = c.category_id
)
GROUP BY
a.actor_id,
a.first_name,
a.last_name


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然后......呼啦啦.The output shows the result correctly,不需要的CROSS JOIN,Because one of the join predicates is missing：是的,This tool has been of great help！Let's fix the query entered.Let's fix the query entered：Correct input

SELECT
a.first_name,
a.last_name,
count(c.category_id)
FROM
actor a,
film_actor fa,
film f,
film_category fc,
category c
WHERE a.actor_id = fa.actor_id
AND fa.film_id = f.film_id
AND f.film_id = fc.film_id -- This was missing
AND fc.category_id = c.category_id
GROUP BY
a.actor_id,
a.first_name,
a.last_name


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固定输出

SELECT
a.first_name,
a.last_name,
count(c.category_id)
FROM actor a
JOIN film_actor fa
ON a.actor_id = fa.actor_id
JOIN film f
ON fa.film_id = f.film_id
JOIN film_category fc
ON f.film_id = fc.film_id
JOIN category c
ON fc.category_id = c.category_id
GROUP BY
a.actor_id,
a.first_name,
a.last_name


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如果你使用OracleThe arcane outer join syntax(+) （或者SQL Server的*= ,It has been unsupported for a while）,这也是可行的.You may have such an input：输入

SELECT
a.first_name,
a.last_name,
count(c.category_id)
FROM
actor a,
film_actor fa,
film f,
film_category fc,
category c
WHERE a.actor_id = fa.actor_id(+)
AND fa.film_id = f.film_id(+)
AND f.film_id = fc.film_id(+)
AND fc.category_id(+) = c.category_id
GROUP BY
a.actor_id,
a.first_name,
a.last_name


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产生这样的输出

SELECT
a.first_name,
a.last_name,
count(c.category_id)
FROM actor a
LEFT OUTER JOIN film_actor fa
ON a.actor_id = fa.actor_id
LEFT OUTER JOIN film f
ON fa.film_id = f.film_id
LEFT OUTER JOIN (
film_category fc
RIGHT OUTER JOIN category c
ON fc.category_id = c.category_id
)
ON f.film_id = fc.film_id
GROUP BY
a.actor_id,
a.first_name,
a.last_name


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呃,哇.又来了!其中一个(+) The symbol is on the wrong side,That's why we got thisRIGHT OUTER JOIN .This tool shows again,The old syntax is error-prone.Let's fix it.Correct input

SELECT
a.first_name,
a.last_name,
count(c.category_id)
FROM
actor a,
film_actor fa,
film f,
film_category fc,
category c
WHERE a.actor_id = fa.actor_id(+)
AND fa.film_id = f.film_id(+)
AND f.film_id = fc.film_id(+)
AND fc.category_id = c.category_id(+)
GROUP BY
a.actor_id,
a.first_name,
a.last_name


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固定输出

SELECT
a.first_name,
a.last_name,
count(c.category_id)
FROM actor a
LEFT OUTER JOIN film_actor fa
ON a.actor_id = fa.actor_id
LEFT OUTER JOIN film f
ON fa.film_id = f.film_id
LEFT OUTER JOIN film_category fc
ON f.film_id = fc.film_id
LEFT OUTER JOIN category c
ON fc.category_id = c.category_id
GROUP BY
a.actor_id,
a.first_name,
a.last_name


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总结

玩一玩,告诉我们你的想法！

 

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