Add distinct expression for count query

DaoCore/src/main/java/org/greenrobot/greendao/internal/SqlUtils.java

@@ -117,7 +117,14 @@ public static String createSqlSelect(String tablename, String tableAlias, String
 
     /** Creates SELECT COUNT(*) with a trailing space. */
     public static String createSqlSelectCountStar(String tablename, String tableAliasOrNull) {
-        StringBuilder builder = new StringBuilder("SELECT COUNT(*) FROM ");
+        return createSqlSelectCount("*", tablename, tableAliasOrNull);
+    }
+
+    /** Creates SELECT COUNT($expression) with a trailing space. */
+    public static String createSqlSelectCount(String expression, String tablename, String tableAliasOrNull) {
+        StringBuilder builder = new StringBuilder("SELECT COUNT(");
+        builder.append(expression);
+        builder.append(") FROM ");
         builder.append('"').append(tablename).append('"').append(' ');
         if (tableAliasOrNull != null) {
             builder.append(tableAliasOrNull).append(' ');

DaoCore/src/main/java/org/greenrobot/greendao/query/QueryBuilder.java

@@ -276,7 +276,7 @@ public QueryBuilder<T> offset(int offset) {
 
     /**
      * Builds a reusable query object (Query objects can be executed more efficiently than creating a QueryBuilder for
-     * each execution.
+     * each execution.)
      */
     public Query<T> build() {
         StringBuilder builder = createSelectBuilder();
@@ -291,7 +291,7 @@ public Query<T> build() {
 
     /**
      * Builds a reusable query object for low level android.database.Cursor access.
-     * (Query objects can be executed more efficiently than creating a QueryBuilder for each execution.
+     * (Query objects can be executed more efficiently than creating a QueryBuilder for each execution.)
      */
     public CursorQuery buildCursor() {
         StringBuilder builder = createSelectBuilder();
@@ -341,7 +341,7 @@ private int checkAddOffset(StringBuilder builder) {
 
     /**
      * Builds a reusable query object for deletion (Query objects can be executed more efficiently than creating a
-     * QueryBuilder for each execution.
+     * QueryBuilder for each execution.)
      */
     public DeleteQuery<T> buildDelete() {
         if (!joins.isEmpty()) {
@@ -366,7 +366,7 @@ public DeleteQuery<T> buildDelete() {
 
     /**
      * Builds a reusable query object for counting rows (Query objects can be executed more efficiently than creating a
-     * QueryBuilder for each execution.
+     * QueryBuilder for each execution.)
      */
     public CountQuery<T> buildCount() {
         String tablename = dao.getTablename();
@@ -380,6 +380,26 @@ public CountQuery<T> buildCount() {
         return CountQuery.create(dao, sql, values.toArray());
     }
 
+    /**
+     * Builds a reusable query object for counting optionally distinct rows according to a column expression.
+     * (Query objects can be executed more efficiently than creating a QueryBuilder for each execution.)
+     *
+     * @param expression column or expression that involves columns to which the COUNT function should be applied
+     * @param distinct whether the COUNT should be DISTINCT instead of ALL
+     */
+    public CountQuery<T> buildCount(String expression, boolean distinct) {
+        String tablename = dao.getTablename();
+        String optionExpression = distinct ? "DISTINCT " + expression : expression;
+        String baseSql = SqlUtils.createSqlSelectCount(optionExpression, tablename, tablePrefix);
+        StringBuilder builder = new StringBuilder(baseSql);
+        appendJoinsAndWheres(builder, tablePrefix);
+
+        String sql = builder.toString();
+        checkLog(sql);
+
+        return CountQuery.create(dao, sql, values.toArray());
+    }
+
     private void checkLog(String sql) {
         if (LOG_SQL) {
             DaoLog.d("Built SQL for query: " + sql);

tests/DaoTest/src/androidTest/java/org/greenrobot/greendao/daotest/query/CountQueryTest.java

@@ -20,6 +20,7 @@
 
 import java.util.ArrayList;
 
+import org.greenrobot.greendao.daotest.TestEntityDao;
 import org.greenrobot.greendao.daotest.entity.TestEntityTestBase;
 import org.greenrobot.greendao.query.CountQuery;
 import org.greenrobot.greendao.query.Query;
@@ -123,4 +124,19 @@ public void testBuildQueryAndCountQuery() {
         assertEquals(1, countQuery.count());
     }
 
+    public void testDistinctExpressionCountQuery() {
+        int value = getSimpleInteger(1);
+        CountQuery<TestEntity> query = dao.queryBuilder().buildCount(Properties.SimpleInteger.columnName, true);
+        assertEquals(0, query.count());
+
+        ArrayList<TestEntity> inserted = insert(3);
+        assertEquals(3, query.count());
+
+        inserted.get(2).setSimpleInteger(value);
+        dao.update(inserted.get(2));
+        assertEquals(2, query.count());
+
+        dao.deleteAll();
+        assertEquals(0, query.count());
+    }
 }