15.38. The SELECT clause

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The `SELECT` clause identifies which objects and values to return as the query results.
The expressions discussed in [Expressions](#hql-expressions) are all valid select expressions, except where otherwise noted.
See the section [Hibernate Query API](#hql-api) for information on handling the results depending on the types of values specified in the `SELECT` clause.

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There is a particular expression type that is only valid in the select clause.
Hibernate calls this "dynamic instantiation".
JPQL supports some of that feature and calls it a "constructor expression".

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So rather than dealing with the `Object[]` (again, see [Hibernate Query API](#hql-api)) here we are wrapping the values in a type-safe java object that will be returned as the results of the query.

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<div id="hql-select-clause-dynamic-instantiation-example" class="exampleblock">
<div class="title">Example 392. Dynamic HQL and JPQL instantiation example</div>
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<pre class="prettyprint highlight">`public class CallStatistics {

    private final long count;
    private final long total;
    private final int min;
    private final int max;
    private final double abg;

    public CallStatistics(long count, long total, int min, int max, double abg) {
        this.count = count;
        this.total = total;
        this.min = min;
        this.max = max;
        this.abg = abg;
    }

    //Getters and setters omitted for brevity
}

CallStatistics callStatistics = entityManager.createQuery(
    "select new org.hibernate.userguide.hql.CallStatistics(" +
    "    count(c), " +
    "    sum(c.duration), " +
    "    min(c.duration), " +
    "    max(c.duration), " +
    "    avg(c.duration)" +
    ")  " +
    "from Call c ", CallStatistics.class )
.getSingleResult();`</pre>
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The class reference must be fully qualified and it must have a matching constructor.

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The class here need not be mapped.
If it does represent an entity, the resulting instances are returned in the NEW state (not managed!).

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HQL supports additional "dynamic instantiation" features.
First, the query can specify to return a `List` rather than an `Object[]` for scalar results:

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<div id="hql-select-clause-dynamic-list-instantiation-example" class="exampleblock">
<div class="title">Example 393. Dynamic instantiation example - list</div>
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<pre class="prettyprint highlight">`List&lt;List&gt; phoneCallDurations = entityManager.createQuery(
    "select new list(" +
    "    p.number, " +
    "    c.duration " +
    ")  " +
    "from Call c " +
    "join c.phone p ", List.class )
.getResultList();`</pre>
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The results from this query will be a `List&lt;List&gt;` as opposed to a `List&lt;Object[]&gt;`

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HQL also supports wrapping the scalar results in a `Map`.

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<div id="hql-select-clause-dynamic-map-instantiation-example" class="exampleblock">
<div class="title">Example 394. Dynamic instantiation example - map</div>
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<pre class="prettyprint highlight">`List&lt;Map&gt; phoneCallTotalDurations = entityManager.createQuery(
    "select new map(" +
    "    p.number as phoneNumber , " +
    "    sum(c.duration) as totalDuration, " +
    "    avg(c.duration) as averageDuration " +
    ")  " +
    "from Call c " +
    "join c.phone p " +
    "group by p.number ", Map.class )
.getResultList();`</pre>
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The results from this query will be a `List&lt;Map&lt;String, Object&gt;&gt;` as opposed to a `List&lt;Object[]&gt;`.
The keys of the map are defined by the aliases given to the select expressions.
If the user doesn&#8217;t assign aliases, the key will be the index of each particular result set column (e.g. 0, 1, 2, etc).

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