[#7430] ResultQuery.fetchOne() should not fetch second record on a LI…

…MIT 1 query

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

@@ -532,7 +532,7 @@ public final <U> U fetchOne(Name fieldName, Converter<?, ? extends U> converter)
 
     @Override
     public final R fetchOne() {
-        return Tools.fetchOne(fetchLazy());
+        return Tools.fetchOne(fetchLazy(), hasLimit1());
     }
 
     @Override
@@ -627,7 +627,7 @@ public final <U> U fetchSingle(Name fieldName, Converter<?, ? extends U> convert
 
     @Override
     public final R fetchSingle() {
-        return Tools.fetchSingle(fetchLazy());
+        return Tools.fetchSingle(fetchLazy(), hasLimit1());
     }
 
     @Override
@@ -1475,4 +1475,14 @@ public final Result<R> call() throws Exception {
             return fetch();
         }
     }
+
+    @SuppressWarnings("rawtypes")
+    private final boolean hasLimit1() {
+        if (this instanceof SelectQueryImpl) {
+            Limit l = ((SelectQueryImpl) this).getLimit();
+            return !l.withTies()                                          && l.limitOne();
+        }
+
+        return false;
+    }
 }

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

@@ -360,12 +360,23 @@ public final Clause[] clauses(Context<?> ctx) {
     }
 
     /**
-     * Whether this limit has an offset of zero
+     * Whether this limit has a limit of zero
      */
     final boolean limitZero() {
         return numberOfRows == null;
     }
 
+    /**
+     * Whether this limit has a limit of one
+     */
+    final boolean limitOne() {
+        return !limitZero()
+            && !withTies()
+
+            && numberOfRows instanceof Param
+            && Integer.valueOf(1).equals(((Param<?>) numberOfRows).getValue());
+    }
+
     /**
      * Whether this limit has an offset of zero
      */

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

@@ -1705,11 +1705,31 @@ else if (size == 1)
      *             element
      */
     static final <R extends Record> R fetchOne(Cursor<R> cursor) throws TooManyRowsException {
+        return fetchOne(cursor, false);
+    }
+
+    /**
+     * Get the only element from a cursor or <code>null</code>, or throw an
+     * exception.
+     * <p>
+     * [#2373] This method will always close the argument cursor, as it is
+     * supposed to be completely consumed by this method.
+     *
+     * @param cursor The cursor
+     * @param hasLimit1 Whether a LIMIT clause is present that guarantees at
+     *            most one row
+     * @return The only element from the cursor or <code>null</code>
+     * @throws TooManyRowsException Thrown if the cursor returns more than one
+     *             element
+     */
+    static final <R extends Record> R fetchOne(Cursor<R> cursor, boolean hasLimit1) throws TooManyRowsException {
         try {
 
             // [#7001] Fetching at most two rows rather than at most one row
             //         (and then checking of additional rows) improves debug logs
-            Result<R> result = cursor.fetchNext(2);
+            // [#7430] Avoid fetching the second row (additional overhead) if
+            //         there is a guarantee of at most one row
+            Result<R> result = cursor.fetchNext(hasLimit1 ? 1 : 2);
             int size = result.size();
 
             if (size == 0)
@@ -1737,11 +1757,31 @@ else if (size == 1)
      *             element
      */
     static final <R extends Record> R fetchSingle(Cursor<R> cursor) throws NoDataFoundException, TooManyRowsException {
+        return fetchSingle(cursor, false);
+    }
+
+    /**
+     * Get the only element from a cursor, or throw an exception.
+     * <p>
+     * [#2373] This method will always close the argument cursor, as it is
+     * supposed to be completely consumed by this method.
+     *
+     * @param cursor The cursor
+     * @param hasLimit1 Whether a LIMIT clause is present that guarantees at
+     *            most one row
+     * @return The only element from the cursor
+     * @throws NoDataFoundException Thrown if the cursor did not return any rows
+     * @throws TooManyRowsException Thrown if the cursor returns more than one
+     *             element
+     */
+    static final <R extends Record> R fetchSingle(Cursor<R> cursor, boolean hasLimit1) throws NoDataFoundException, TooManyRowsException {
         try {
 
             // [#7001] Fetching at most two rows rather than at most one row
             //         (and then checking of additional rows) improves debug logs
-            Result<R> result = cursor.fetchNext(2);
+            // [#7430] Avoid fetching the second row (additional overhead) if
+            //         there is a guarantee of at most one row
+            Result<R> result = cursor.fetchNext(hasLimit1 ? 1 : 2);
             int size = result.size();
 
             if (size == 0)