[#3746] Add DSLContext.fetchExists(Select<?>)

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

@@ -5863,6 +5863,49 @@ public interface DSLContext extends Scope {
      */
     int fetchCount(Table<?> table, Condition condition) throws DataAccessException;
 
+    /**
+     * Check if a {@link Select} would return any records, if it were executed.
+     * <p>
+     * This wraps a pre-existing <code>SELECT</code> query in another one to
+     * check for result existence, 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 EXISTS (
+     *   SELECT id, title FROM book WHERE title LIKE '%a%'
+     * )
+     * </pre></code>
+     *
+     * @param query The wrapped query
+     * @return The <code>EXISTS(...)</code> result
+     * @throws DataAccessException if something went wrong executing the query
+     */
+    boolean fetchExists(Select<?> query) throws DataAccessException;
+
+    /**
+     * Check if a table has any records.
+     * <p>
+     * This executes <code><pre>SELECT EXISTS(SELECT * FROM table)</pre></code>
+     *
+     * @param table The table whose records to count
+     * @return The number or records in the table
+     * @throws DataAccessException if something went wrong executing the query
+     */
+    boolean fetchExists(Table<?> table) throws DataAccessException;
+
+    /**
+     * Check if a table has any records that satisfy a condition.
+     * <p>
+     * This executes <code><pre>SELECT EXISTS(SELECT * FROM table WHERE condition)</pre></code>
+     *
+     * @param table The table whose records to count
+     * @return The number or records in the table
+     * @throws DataAccessException if something went wrong executing the query
+     */
+    boolean fetchExists(Table<?> table, Condition condition) throws DataAccessException;
+
     /**
      * Execute a {@link Query} in the context of this <code>DSLContext</code>.
      *

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

@@ -2241,6 +2241,21 @@ public class DefaultDSLContext extends AbstractScope implements DSLContext, Seri
         return selectCount().from(table).where(condition).fetchOne(0, int.class);
     }
 
+    @Override
+    public boolean fetchExists(Select<?> query) throws DataAccessException {
+        return selectOne().whereExists(query).fetchOne() != null;
+    }
+
+    @Override
+    public boolean fetchExists(Table<?> table) throws DataAccessException {
+        return fetchExists(table, trueCondition());
+    }
+
+    @Override
+    public boolean fetchExists(Table<?> table, Condition condition) throws DataAccessException {
+        return fetchExists(selectOne().from(table).where(condition));
+    }
+
     @Override
     public int execute(Query query) {
         final Configuration previous = Utils.getConfiguration(query);