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Java > Open Source Codes > org > apache > derby > impl > sql > compile > CountAggregateDefinition


1 /*
2
3    Derby - Class org.apache.derby.impl.sql.compile.CountAggregateDefinition
4
5    Licensed to the Apache Software Foundation (ASF) under one or more
6    contributor license agreements. See the NOTICE file distributed with
7    this work for additional information regarding copyright ownership.
8    The ASF licenses this file to you under the Apache License, Version 2.0
9    (the "License"); you may not use this file except in compliance with
10    the License. You may obtain a copy of the License at
11
12       http://www.apache.org/licenses/LICENSE-2.0
13
14    Unless required by applicable law or agreed to in writing, software
15    distributed under the License is distributed on an "AS IS" BASIS,
16    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
17    See the License for the specific language governing permissions and
18    limitations under the License.
19
20  */
21
22 package org.apache.derby.impl.sql.compile;
23
24 import org.apache.derby.iapi.sql.conn.LanguageConnectionContext;
25 import org.apache.derby.iapi.types.DataTypeDescriptor;
26
27 import org.apache.derby.impl.sql.execute.CountAggregator;
28
29 import org.apache.derby.catalog.TypeDescriptor;
30
31 import org.apache.derby.iapi.reference.ClassName;
32
33
34 /**
35  * Defintion for the COUNT()/COUNT(*) aggregates.
36  *
37  * @author jamie
38  */
39 public class CountAggregateDefinition
40         implements AggregateDefinition
41 {
42     /**
43      * Niladic constructor. Does nothing. For ease
44      * Of use, only.
45      */
46     public CountAggregateDefinition() { super(); }
47
48     /**
49      * Determines the result datatype. We can run
50      * count() on anything, and it always returns a
51      * INTEGER (java.lang.Integer).
52      *
53      * @param inputType the input type, either a user type or a java.lang object
54      *
55      * @return the output Class (null if cannot operate on
56      * value expression of this type.
57      */
58     public final TypeDescriptor getAggregator(TypeDescriptor inputType,
59                 StringBuffer JavaDoc aggregatorClass)
60     {
61         aggregatorClass.append( ClassName.CountAggregator);
62         /*
63         ** COUNT never returns NULL
64         */
65         return DataTypeDescriptor.getBuiltInDataTypeDescriptor(java.sql.Types.INTEGER, false);
66     }
67
68 }
69
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