[#2200] Add Executor.fetchCount(Select<?>) and Select.fetchCount() to

replace the projection by a COUNT(*) query

jOOQ-test/src/org/jooq/test/_/testcases/AggregateWindowFunctionTests.java

@@ -59,6 +59,7 @@ import static org.jooq.impl.Factory.cumeDist;
 import static org.jooq.impl.Factory.denseRank;
 import static org.jooq.impl.Factory.firstValue;
 import static org.jooq.impl.Factory.groupConcat;
+import static org.jooq.impl.Factory.inline;
 import static org.jooq.impl.Factory.lag;
 import static org.jooq.impl.Factory.lead;
 import static org.jooq.impl.Factory.listAgg;
@@ -68,6 +69,7 @@ import static org.jooq.impl.Factory.median;
 import static org.jooq.impl.Factory.min;
 import static org.jooq.impl.Factory.minDistinct;
 import static org.jooq.impl.Factory.ntile;
+import static org.jooq.impl.Factory.one;
 import static org.jooq.impl.Factory.percentRank;
 import static org.jooq.impl.Factory.rank;
 import static org.jooq.impl.Factory.regrAvgX;
@@ -80,6 +82,9 @@ import static org.jooq.impl.Factory.regrSXY;
 import static org.jooq.impl.Factory.regrSYY;
 import static org.jooq.impl.Factory.regrSlope;
 import static org.jooq.impl.Factory.rowNumber;
+import static org.jooq.impl.Factory.select;
+import static org.jooq.impl.Factory.selectDistinct;
+import static org.jooq.impl.Factory.selectFrom;
 import static org.jooq.impl.Factory.stddevPop;
 import static org.jooq.impl.Factory.stddevSamp;
 import static org.jooq.impl.Factory.sum;
@@ -280,6 +285,23 @@ extends BaseTest<A, AP, B, S, B2S, BS, L, X, DATE, BOOL, D, T, U, UU, I, IPK, T7
         assertEquals(4, (int) result3.get(1).getValue(2, Integer.class));
     }
 
+    @Test
+    public void testFetchCount() throws Exception {
+        assertEquals(1, create().fetchCount(select(one().as("x"))));
+        assertEquals(1, create().select(one().as("x")).fetchCount());
+
+        assertEquals(4, create().fetchCount(select(TBook_ID(), TBook_TITLE()).from(TBook())));
+        assertEquals(4, create().select(TBook_ID(), TBook_TITLE()).from(TBook()).fetchCount());
+
+        assertEquals(3, create().fetchCount(selectDistinct(TBook_ID(), TBook_TITLE()).from(TBook()).where(TBook_ID().in(1, 2, 3))));
+        assertEquals(2, create().fetchCount(selectFrom(TBook()).limit(2)));
+        assertEquals(2, create().fetchCount(selectFrom(TBook()).limit(2).offset(1)));
+        assertEquals(2, create().fetchCount(
+            select(TBook_TITLE()).from(TBook()).where(TBook_ID().eq(1))
+            .union(
+            select(inline("abc")))));
+    }
+
     @Test
     public void testCountDistinct() throws Exception {
 

jOOQ-test/src/org/jooq/test/jOOQAbstractTest.java

@@ -1717,6 +1717,11 @@ public abstract class jOOQAbstractTest<
         new AggregateWindowFunctionTests(this).testAggregateFunctions();
     }
 
+    @Test
+    public void testFetchCount() throws Exception {
+        new AggregateWindowFunctionTests(this).testFetchCount();
+    }
+
     @Test
     public void testCountDistinct() throws Exception {
         new AggregateWindowFunctionTests(this).testCountDistinct();

jOOQ/src/main/java/org/jooq/Select.java

@@ -37,6 +37,8 @@ package org.jooq;
 
 import java.util.List;
 
+import org.jooq.exception.DataAccessException;
+
 /**
  * A {@link Query} that can provide a {@link Result} after execution
  *
@@ -73,4 +75,27 @@ public interface Select<R extends Record> extends ResultQuery<R>, TableLike<R>,
      * All fields selected in this query
      */
     List<Field<?>> getSelect();
+
+    /**
+     * Execute this query in the context of its attached executor and return
+     * a <code>COUNT(*)</code> value.
+     * <p>
+     * This wraps a pre-existing <code>SELECT</code> query in another one to
+     * calculate the <code>COUNT(*)</code> value, without modifying the original
+     * <code>SELECT</code>. An example: <code><pre>
+     * -- Original query:
+     * SELECT id, title FROM book WHERE title LIKE '%a%'
+     *
+     * -- Wrapped query:
+     * SELECT count(*) FROM (
+     *   SELECT id, title FROM book WHERE title LIKE '%a%'
+     * )
+     * </pre></code> This is particularly useful for those databases that do not
+     * support the <code>COUNT(*) OVER()</code> window function to calculate
+     * total results in paged queries.
+     *
+     * @return The <code>COUNT(*)</code> result
+     * @throws DataAccessException if something went wrong executing the query
+     */
+    int fetchCount() throws DataAccessException;
 }

jOOQ/src/main/java/org/jooq/impl/AbstractSelect.java

@@ -48,6 +48,7 @@ import org.jooq.Result;
 import org.jooq.Row;
 import org.jooq.Select;
 import org.jooq.Table;
+import org.jooq.exception.DataAccessException;
 
 /**
  * A common base class for all <code>SELECT</code> statements.
@@ -62,6 +63,11 @@ abstract class AbstractSelect<R extends Record> extends AbstractResultQuery<R> i
         super(configuration);
     }
 
+    @Override
+    public final int fetchCount() throws DataAccessException {
+        return new Executor(getConfiguration()).fetchCount(this);
+    }
+
     @Override
     public final Select<R> union(Select<? extends R> select) {
         return new Union<R>(getConfiguration(), this, select, CombineOperator.UNION);

jOOQ/src/main/java/org/jooq/impl/Executor.java

@@ -5328,6 +5328,32 @@ public class Executor implements Configuration {
         }
     }
 
+    /**
+     * Execute a {@link Select} query in the context of this executor and return
+     * a <code>COUNT(*)</code> value.
+     * <p>
+     * This wraps a pre-existing <code>SELECT</code> query in another one to
+     * calculate the <code>COUNT(*)</code> value, without modifying the original
+     * <code>SELECT</code>. An example: <code><pre>
+     * -- Original query:
+     * SELECT id, title FROM book WHERE title LIKE '%a%'
+     *
+     * -- Wrapped query:
+     * SELECT count(*) FROM (
+     *   SELECT id, title FROM book WHERE title LIKE '%a%'
+     * )
+     * </pre></code> This is particularly useful for those databases that do not
+     * support the <code>COUNT(*) OVER()</code> window function to calculate
+     * total results in paged queries.
+     *
+     * @param query The wrapped query
+     * @return The <code>COUNT(*)</code> result
+     * @throws DataAccessException if something went wrong executing the query
+     */
+    public final int fetchCount(Select<?> query) throws DataAccessException {
+        return selectCount().from(query).fetchOne(0, int.class);
+    }
+
     /**
      * Execute a {@link Query} in the context of this executor.
      *

jOOQ/src/main/java/org/jooq/impl/SelectImpl.java

@@ -153,6 +153,11 @@ class SelectImpl<R extends Record> extends AbstractDelegatingQuery<Select<R>> im
         return (SelectQuery<R>) getDelegate();
     }
 
+    @Override
+    public final int fetchCount() {
+        return getDelegate().fetchCount();
+    }
+
     /**
      * This method must be able to return both incompatible types
      * SelectSelectStep&lt;Record> and SelectSelectStep&lt;R>