[#579] SQL syntax error when using Factory.selectOne() in a subquery - first implementation attempt

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

@@ -3544,7 +3544,7 @@ public abstract class jOOQAbstractTest<
         assertEquals(Arrays.asList(1, 2, 3, 4), books.getValues(b_ID));
     }
 
-    // @Test TODO [#579] re-enable this test when fixing this bug
+    // @Test // TODO [#579] re-enable this test when fixing this bug
     public void testUnaliasedSubqueryProjections() throws Exception {
         // Test whether unaliased literals in subquery projections are correctly
         // handled

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

@@ -47,6 +47,18 @@ package org.jooq;
  */
 public interface RenderContext extends Context<RenderContext> {
 
+    /**
+     * Peek the next alias that will be generated by {@link #nextAlias()}
+     */
+    String peekAlias();
+
+    /**
+     * Return a new alias that is unique for the scope of one query. These
+     * aliases are sometimes needed when unaliased projections are defined in
+     * subqueries, which can lead to syntax errors.
+     */
+    String nextAlias();
+
     /**
      * Render the context's underlying SQL statement
      */

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

@@ -52,6 +52,7 @@ class DefaultRenderContext extends AbstractContext<RenderContext> implements Ren
 
     private final StringBuilder sql;
     private boolean             inline;
+    private int                 alias;
 
     DefaultRenderContext(Configuration configuration) {
         super(configuration);
@@ -71,6 +72,16 @@ class DefaultRenderContext extends AbstractContext<RenderContext> implements Ren
     // RenderContext API
     // ------------------------------------------------------------------------
 
+    @Override
+    public final String peekAlias() {
+        return "alias_" + (alias + 1);
+    }
+
+    @Override
+    public final String nextAlias() {
+        return "alias_" + (++alias);
+    }
+
     @Override
     public final String render() {
         return sql.toString();