Add support for count(distinct ...)

Resolves #112

Author: jeffgbutler

CHANGELOG.md

@@ -2,6 +2,15 @@
 
 This log will detail notable changes to MyBatis Dynamic SQL. Full details are available on the GitHub milestone pages.
 
+## Release 1.1.3 - Unreleased
+
+GitHub milestone: [https://github.com/mybatis/mybatis-dynamic-sql/issues?q=milestone%3A1.1.2+](https://github.com/mybatis/mybatis-dynamic-sql/issues?q=milestone%3A1.1.3+)
+
+### Added
+
+- Added support for `count(distinct ...)` [#112](https://github.com/mybatis/mybatis-dynamic-sql/issues/112)
+
+
 ## Release 1.1.2 - July 5, 2019
 
 GitHub milestone: [https://github.com/mybatis/mybatis-dynamic-sql/issues?q=milestone%3A1.1.2+](https://github.com/mybatis/mybatis-dynamic-sql/issues?q=milestone%3A1.1.2+)

src/main/java/org/mybatis/dynamic/sql/SqlBuilder.java

@@ -31,6 +31,7 @@
 import org.mybatis.dynamic.sql.select.aggregate.Avg;
 import org.mybatis.dynamic.sql.select.aggregate.Count;
 import org.mybatis.dynamic.sql.select.aggregate.CountAll;
+import org.mybatis.dynamic.sql.select.aggregate.CountDistinct;
 import org.mybatis.dynamic.sql.select.aggregate.Max;
 import org.mybatis.dynamic.sql.select.aggregate.Min;
 import org.mybatis.dynamic.sql.select.aggregate.Sum;
@@ -200,6 +201,10 @@ static Count count(BasicColumn column) {
         return Count.of(column);
     }
 
+    static CountDistinct countDistinct(BasicColumn column) {
+        return CountDistinct.of(column);
+    }
+    
     static Max max(BasicColumn column) {
         return Max.of(column);
     }

src/main/java/org/mybatis/dynamic/sql/select/aggregate/CountDistinct.java

@@ -0,0 +1,39 @@
+/**
+ *    Copyright 2016-2019 the original author or authors.
+ *
+ *    Licensed under the Apache License, Version 2.0 (the "License");
+ *    you may not use this file except in compliance with the License.
+ *    You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    Unless required by applicable law or agreed to in writing, software
+ *    distributed under the License is distributed on an "AS IS" BASIS,
+ *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *    See the License for the specific language governing permissions and
+ *    limitations under the License.
+ */
+package org.mybatis.dynamic.sql.select.aggregate;
+
+import org.mybatis.dynamic.sql.BasicColumn;
+
+public class CountDistinct extends AbstractAggregate<CountDistinct> {
+    
+    private CountDistinct(BasicColumn column) {
+        super(column);
+    }
+    
+    @Override
+    protected String render(String columnName) {
+        return "count(distinct " + columnName + ")"; //$NON-NLS-1$ //$NON-NLS-2$
+    }
+
+    @Override
+    protected CountDistinct copy() {
+        return new CountDistinct(column);
+    }
+    
+    public static CountDistinct of(BasicColumn column) {
+        return new CountDistinct(column);
+    }
+}

src/test/java/examples/groupby/GroupByTest.java

@@ -312,4 +312,24 @@ public void testFetchFirstOnlyAfterGroupBy() {
             assertThat(row.get("COUNT")).isEqualTo(4L);
         }
     }
+
+    @Test
+    public void testCountDistinct() {
+        try (SqlSession session = sqlSessionFactory.openSession()) {
+            GroupByMapper mapper = session.getMapper(GroupByMapper.class);
+        
+            SelectStatementProvider selectStatement = select(countDistinct(lastName).as("count"))
+                    .from(person)
+                    .build()
+                    .render(RenderingStrategy.MYBATIS3);
+            
+            String expected = "select count(distinct last_name) as count from Person";
+            assertThat(selectStatement.getSelectStatement()).isEqualTo(expected);
+            
+            List<Map<String, Object>> rows = mapper.generalSelect(selectStatement);
+            assertThat(rows.size()).isEqualTo(1);
+            Map<String, Object> row = rows.get(0);
+            assertThat(row.get("COUNT")).isEqualTo(2L);
+        }
+    }
 }