Question

This is the correct ordered array with MySQL:

[
  [1330210800000, 1],
  [1330297200000, 6],
  [1330383600000, 10], 
  [1330470000000, 2],
  [1330556400000, 5],
  [1330815600000, 9],
  [1331593200000, 2], 
  [1331852400000, 4],
  [1331938800000, 8],
  [1332111600000, 8],
  [1332198000000, 4], 
  [1332284400000, 8],
  [1332370800000, 3], 
  [1332630000000, 2] 
]

But with PostgreSQL the array is:

[
  [1330588800000, 5], 
  [1332399600000, 3], 
  [1330848000000, 9], 
  [1330416000000, 10], 
  [1331622000000, 2], 
  [1330329600000, 6], 
  [1330502400000, 2], 
  [1332140400000, 8], 
  [1332313200000, 8], 
  [1330243200000, 1], 
  [1332226800000, 4], 
  [1331967600000, 8], 
  [1332658800000, 2], 
  [1331881200000, 4] 
]

The postgreSQL is the order wrong and the dates different and the count of kliks:

This is the query in my controller:

@kliks = Klik.count( :group => "DATE( created_at )" )
         .map{|k, v| [(Time.parse(k).to_i * 1000), v] }

Answer 1

You haven’t specified any particular order in your query so the database is free to return your results in any order it wants. Apparently MySQL is ordering the results as a side effect of its GROUP BY but PostgreSQL won’t necessarily do that. So your first “bug” is just an incorrect assumption on your part. If you want the database to do the sorting then you want something like:

Klik.count(:group => 'date(created_at)', :order => :date_created_at)

If you throw out the * 1000 and sort the integer timestamps:

1330210800, 1,  MySQL
1330243200, 1,  PostgreSQL

1330297200, 6,  MySQL
1330329600, 6,  PostgreSQL

1330383600, 10, MySQL
1330416000, 10, PostreSQL

...

You’ll see that they do actually line up quite nicely and the integer timestamps differ by 32400s (AKA 9 hours) or 28800s (AKA 8 hours or 9 hours with a DST adjustment) in each MySQL/PostgreSQL pair. Presumably you’re including a time zone (with DST) in one of your conversions while the other is left in UTC.