Added some sections to the manual
This commit is contained in:
Lukas Eder
parent
6095d5c1c4
commit
32feb254dc
@ -45,7 +45,7 @@ Condition notExists(Select<?> query);</pre>
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<p>When you create such a Condition, it can then be connected to any
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other condition using AND, OR operators (see also the manual's section
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on
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<a href="" title="jOOQ Manual reference: ">Conditions</a>). Because of this verbosity, there are also quite a few
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<a href="<?=$root?>/manual/DSL/CONDITION/" title="jOOQ Manual reference: Conditions">Conditions</a>). Because of this verbosity, there are also quite a few
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convenience methods, where they might be useful. For instance in the
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<a href="https://github.com/lukaseder/jOOQ/blob/master/jOOQ/src/main/java/org/jooq/Condition.java" title="Internal API reference: org.jooq.Condition">org.jooq.Condition</a> itself: </p>
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@ -7,7 +7,9 @@ function printH1() {
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print "Other types of nested SELECT";
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}
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function getSlogan() {
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return "";
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return "Apart from the most common IN and EXISTS clauses that encourage
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the use of nested selects, SQL knows a few more syntaxes to make use
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of such constructs. ";
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}
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function printContent() {
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global $root;
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@ -16,7 +18,128 @@ function printContent() {
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<tr>
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<td align="left" valign="top"><a href="<?=$root?>/manual/">The jOOQ User Manual</a> : <a href="<?=$root?>/manual/DSL/">DSL or fluent API. Where SQL meets Java</a> : <a href="<?=$root?>/manual/DSL/NESTED/">Other types of nested SELECT</a></td><td align="right" valign="top" style="white-space: nowrap"><a href="<?=$root?>/manual/DSL/EXISTS/" title="Previous section: Nested SELECT using the EXISTS operator">previous</a> : <a href="<?=$root?>/manual/DSL/UNION/" title="Next section: UNION and other set operations">next</a></td>
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</tr>
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</table><br><table cellpadding="0" cellspacing="0" border="0" width="100%">
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</table>
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<h2>Comparison with single-field SELECT clause</h2>
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<p>If you can ensure that a nested SELECT will only return one Record
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with one Field, then you can test for equality. This is how it is done
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in SQL: </p>
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<table width="100%" cellpadding="0" cellspacing="0">
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<tr>
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<td width="50%" class="left">
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<pre class="prettyprint lang-sql">
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SELECT *
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FROM T_BOOK
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WHERE T_BOOK.AUTHOR_ID = (
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SELECT ID
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FROM T_AUTHOR
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WHERE LAST_NAME = 'Orwell')</pre>
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</td><td width="50%" class="right">
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<pre class="prettyprint lang-java">
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create.select()
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.from(T_BOOK)
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.where(TBook.AUTHOR_ID.equal(
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create.select(TAuthor.ID)
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.from(T_AUTHOR)
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.where(TAuthor.LAST_NAME.equal("Orwell"))));</pre>
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</td>
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</tr>
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</table>
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<p>More examples like the above can be guessed from the
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<a href="https://github.com/lukaseder/jOOQ/blob/master/jOOQ/src/main/java/org/jooq/Field.java" title="Internal API reference: org.jooq.Field">org.jooq.Field</a> API, as documented in the manual's section about
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<a href="<?=$root?>/manual/DSL/CONDITION/" title="jOOQ Manual reference: Conditions">Conditions</a>. For the = operator, the available comparisons are these:</p>
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<pre class="prettyprint lang-java">
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Condition equal(Select<?> query);
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Condition equalAny(Select<?> query);
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Condition equalSome(Select<?> query);
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Condition equalAll(Select<?> query);</pre>
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<h2>Selecting from a SELECT - SELECT acts as a Table</h2>
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<p>Often, you need to nest a SELECT statement simply because SQL is
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limited in power. For instance, if you want to find out which author
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has written the most books, then you cannot do this: </p>
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<pre class="prettyprint lang-sql">
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SELECT AUTHOR_ID, count(*) books
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FROM T_BOOK
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GROUP BY AUTHOR_ID
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ORDER BY books DESC</pre>
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<p>Instead, you have to do this (or something similar). For jOOQ, this
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is an excellent example, combining various SQL features into a single
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statement. Here's how to do it: </p>
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<table width="100%" cellpadding="0" cellspacing="0">
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<tr>
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<td width="50%" class="left">
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<pre class="prettyprint lang-sql">
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SELECT nested.* FROM (
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SELECT AUTHOR_ID, count(*) books
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FROM T_BOOK
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GROUP BY AUTHOR_ID
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) nested
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ORDER BY nested.books DESC
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</pre>
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</td><td width="50%" class="right">
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<pre class="prettyprint lang-java">
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Table<Record> nested =
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create.select(TBook.AUTHOR_ID, create.count().as("books"))
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.from(T_BOOK)
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.groupBy(TBook.AUTHOR_ID).asTable("nested");
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create.select(nested.getFields())
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.from(nested)
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.orderBy(nested.getField("books"));</pre>
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</td>
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</tr>
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</table>
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<p>You'll notice how some verbosity seems inevitable when you combine nested SELECT statements with aliasing. </p>
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<h2>Selecting a SELECT - SELECT acts as a Field</h2>
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<p>Now SQL is even more powerful than that. You can also have SELECT
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statements, wherever you can have Fields. It get's harder and harder
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to find good examples, because there is always an easier way to
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express the same thing. But why not just count the number of books the
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really hard way? :-) But then again, maybe you want to take advantage
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of <a href="http://lukaseder.wordpress.com/2011/09/02/oracle-scalar-subquery-caching/" title="Oracle Scalar Subquery Caching with jOOQ">Oracle Scalar Subquery Caching</a>
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</p>
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<table width="100%" cellpadding="0" cellspacing="0">
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<tr>
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<td width="50%" class="left">
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<pre class="prettyprint lang-sql">
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SELECT LAST_NAME, (
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SELECT COUNT(*)
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FROM T_BOOK
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WHERE T_BOOK.AUTHOR_ID = T_AUTHOR.ID) books
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FROM T_AUTHOR
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ORDER BY books DESC
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</pre>
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</td><td width="50%" class="right">
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<pre class="prettyprint lang-java">
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// The type of books cannot be inferred from the Select<?>
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Field<Object> books =
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create.select(create.count())
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.from(T_BOOK)
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.where(TBook.AUTHOR_ID.equal(TAuthor.ID)).asField("books");
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create.select(TAuthor.ID, books)
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.from(T_AUTHOR)
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.orderBy(books, TAuthor.ID));</pre>
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</td>
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</tr>
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</table>
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<br><table cellpadding="0" cellspacing="0" border="0" width="100%">
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<tr>
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<td align="left" valign="top"><a href="<?=$root?>/manual/">The jOOQ User Manual</a> : <a href="<?=$root?>/manual/DSL/">DSL or fluent API. Where SQL meets Java</a> : <a href="<?=$root?>/manual/DSL/NESTED/">Other types of nested SELECT</a></td><td align="right" valign="top" style="white-space: nowrap"><a href="<?=$root?>/manual/DSL/EXISTS/" title="Previous section: Nested SELECT using the EXISTS operator">previous</a> : <a href="<?=$root?>/manual/DSL/UNION/" title="Next section: UNION and other set operations">next</a></td>
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</tr>
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@ -2531,7 +2531,7 @@ Condition notExists(Select<?> query);</java>
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<p>When you create such a Condition, it can then be connected to any
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other condition using AND, OR operators (see also the manual's section
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on
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<reference id="CONDITIONS" title="Conditions"/>). Because of this verbosity, there are also quite a few
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<reference id="CONDITION" title="Conditions"/>). Because of this verbosity, there are also quite a few
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convenience methods, where they might be useful. For instance in the
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<reference class="org.jooq.Condition"/> itself: </p>
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@ -2576,6 +2576,112 @@ create.select()
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<section id="NESTED">
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<title>Other types of nested SELECT</title>
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<slogan>Apart from the most common IN and EXISTS clauses that encourage
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the use of nested selects, SQL knows a few more syntaxes to make use
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of such constructs. </slogan>
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<content>
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<h2>Comparison with single-field SELECT clause</h2>
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<p>If you can ensure that a nested SELECT will only return one Record
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with one Field, then you can test for equality. This is how it is done
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in SQL: </p>
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<code-pair>
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<sql>
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SELECT *
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FROM T_BOOK
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WHERE T_BOOK.AUTHOR_ID = (
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SELECT ID
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FROM T_AUTHOR
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WHERE LAST_NAME = 'Orwell')</sql><java>
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create.select()
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.from(T_BOOK)
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.where(TBook.AUTHOR_ID.equal(
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create.select(TAuthor.ID)
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.from(T_AUTHOR)
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.where(TAuthor.LAST_NAME.equal("Orwell"))));</java>
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</code-pair>
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<p>More examples like the above can be guessed from the
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<reference class="org.jooq.Field"/> API, as documented in the manual's section about
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<reference id="CONDITION" title="Conditions"/>. For the = operator, the available comparisons are these:</p>
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<java>
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Condition equal(Select<?> query);
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Condition equalAny(Select<?> query);
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Condition equalSome(Select<?> query);
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Condition equalAll(Select<?> query);</java>
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<h2>Selecting from a SELECT - SELECT acts as a Table</h2>
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<p>Often, you need to nest a SELECT statement simply because SQL is
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limited in power. For instance, if you want to find out which author
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has written the most books, then you cannot do this: </p>
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<sql>
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SELECT AUTHOR_ID, count(*) books
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FROM T_BOOK
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GROUP BY AUTHOR_ID
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ORDER BY books DESC</sql>
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<p>Instead, you have to do this (or something similar). For jOOQ, this
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is an excellent example, combining various SQL features into a single
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statement. Here's how to do it: </p>
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<code-pair>
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<sql>
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SELECT nested.* FROM (
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SELECT AUTHOR_ID, count(*) books
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FROM T_BOOK
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GROUP BY AUTHOR_ID
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) nested
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ORDER BY nested.books DESC
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</sql><java>
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Table<Record> nested =
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create.select(TBook.AUTHOR_ID, create.count().as("books"))
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.from(T_BOOK)
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.groupBy(TBook.AUTHOR_ID).asTable("nested");
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create.select(nested.getFields())
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.from(nested)
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.orderBy(nested.getField("books"));</java>
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</code-pair>
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<p>You'll notice how some verbosity seems inevitable when you combine nested SELECT statements with aliasing. </p>
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<h2>Selecting a SELECT - SELECT acts as a Field</h2>
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<p>Now SQL is even more powerful than that. You can also have SELECT
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statements, wherever you can have Fields. It get's harder and harder
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to find good examples, because there is always an easier way to
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express the same thing. But why not just count the number of books the
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really hard way? :-) But then again, maybe you want to take advantage
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of <a href="http://lukaseder.wordpress.com/2011/09/02/oracle-scalar-subquery-caching/" title="Oracle Scalar Subquery Caching with jOOQ">Oracle Scalar Subquery Caching</a></p>
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<code-pair>
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<sql>
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SELECT LAST_NAME, (
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SELECT COUNT(*)
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FROM T_BOOK
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WHERE T_BOOK.AUTHOR_ID = T_AUTHOR.ID) books
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FROM T_AUTHOR
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ORDER BY books DESC
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</sql><java>
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// The type of books cannot be inferred from the Select<?>
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Field<Object> books =
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create.select(create.count())
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.from(T_BOOK)
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.where(TBook.AUTHOR_ID.equal(TAuthor.ID)).asField("books");
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create.select(TAuthor.ID, books)
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.from(T_AUTHOR)
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.orderBy(books, TAuthor.ID));</java>
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</code-pair>
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</content>
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</section>
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