fails in mysql
```
*** (s.slick.compiler.QueryCompiler) After phase codeGen:
  ResultSetMapping : Coll[(Int/INTEGER, Option[Int/INTEGER])]
    from s19: CompiledStatement "select 5, sum(5 + 5) from `u` s17 group by 5" : Coll[NominalType(t18)((Int/INTEGER, Option[Int/INTEGER]))]
    map: CompiledMapping : (Int/INTEGER, Option[Int/INTEGER])

[error] Test com.typesafe.slick.testkit.tests.AggregateTest.testGroupBy[mysql] failed: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Unknown column '5' in 'group statement'
[error]     at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
[error]     at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
[error]     at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
[error]     at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
[error]     at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
[error]     at com.mysql.jdbc.Util.getInstance(Util.java:386)
[error]     at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1053)
[error]     at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4120)
[error]     at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4052)
[error]     at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2503)
[error]     at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2664)
[error]     at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2794)
[error]     at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2155)
[error]     at com.mysql.jdbc.PreparedStatement.execute(PreparedStatement.java:1379)
[error]     at scala.slick.jdbc.StatementInvoker.results(StatementInvoker.scala:33)
[error]     at scala.slick.jdbc.StatementInvoker.iteratorTo(StatementInvoker.scala:16)
[error]     at scala.slick.jdbc.Invoker$class.foreach(Invoker.scala:93)
[error]     at scala.slick.jdbc.StatementInvoker.foreach(StatementInvoker.scala:9)
[error]     at scala.slick.jdbc.Invoker$class.build(Invoker.scala:69)
[error]     at scala.slick.jdbc.StatementInvoker.build(StatementInvoker.scala:9)
[error]     at scala.slick.jdbc.Invoker$class.to(Invoker.scala:77)
[error]     at scala.slick.jdbc.StatementInvoker.to(StatementInvoker.scala:9)
[error]     at scala.slick.driver.JdbcExecutorComponent$QueryExecutorDef.run(JdbcExecutorComponent.scala:23)
[error]     at scala.slick.driver.JdbcExecutorComponent$QueryExecutorDef.run(JdbcExecutorComponent.scala:15)
[error]     at com.typesafe.slick.testkit.tests.AggregateTest.testGroupBy(AggregateTest.scala:133)
[error]     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[error]     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
[error]     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
[error]     at java.lang.reflect.Method.invoke(Method.java:597)
[error]     at com.typesafe.slick.testkit.util.Testkit$$anonfun$runChildren$2.apply(Testkit.scala:85)
[error]     at com.typesafe.slick.testkit.util.Testkit$$anonfun$runChildren$2.apply(Testkit.scala:76)
[error]     at scala.collection.TraversableLike$WithFilter$$anonfun$foreach$1.apply(TraversableLike.scala:772)
[error]     at scala.collection.Iterator$class.foreach(Iterator.scala:727)
[error]     at scala.collection.AbstractIterator.foreach(Iterator.scala:1157)
[error]     at scala.collection.IterableLike$class.foreach(IterableLike.scala:72)
[error]     at scala.collection.AbstractIterable.foreach(Iterable.scala:54)
[error]     at scala.collection.TraversableLike$WithFilter.foreach(TraversableLike.scala:771)
[error]     at com.typesafe.slick.testkit.util.Testkit.runChildren(Testkit.scala:76)
[error]     at com.typesafe.slick.testkit.util.SimpleParentRunner.run(SimpleParentRunner.scala:56)
[error]     ...
```