3

I'm running Postgresql 9.6 on Ubuntu 16.04. The collation order is en_ZA.UTF-8. I'm puzzled by how Postgres compares strings:

test=> select 'b' > 'B';
 ?column? 
----------
  f

test=> select 'ba' > 'B';
?column? 
----------
  t

test=> select 'b' = 'B';
?column? 
----------
  f

test=> select 'ba' > 'C';
 ?column?  
----------
 f

The response to the second query doesn't make sense to me.

2

That's just how your locale defines sort order. Obviously upper case letters act as tiebreakers if the string is otherwise identical - then they sort after lower case equivalents. But 'ba' still sorts after 'B' (and 'BA' sorts after 'b').

Compare to results without collation rules:

SELECT   'b' > 'B'
      , 'ba' > 'B'
      , 'ba' > 'C'
      , 'b'  > 'B' COLLATE "C"
      , 'ba' > 'B' COLLATE "C"
      , 'ba' > 'C' COLLATE "C";
 ?column? | ?column? | ?column? | ?column? | ?column? | ?column?
----------+----------+----------+----------+----------+----------
 f        | t        | f        | t        | t        | t

(My current collation setting German_Germany.1252 happens to behave just like your en_ZA.UTF-8.)

  • Erwin, thanks a lot for your comment! Are you aware of a reference that rigorously defines this sorting order -- I'm still not 100% sure how it's supposed to work. – dmitry Feb 28 '17 at 15:56
  • @dmitry: You might investigate the locale definitions of your OS, which provides the rules Postgres uses. – Erwin Brandstetter Feb 28 '17 at 15:59
  • @dmitry it means it's supposed to work: First order lexicographically (case insensitive) and then, only in case of a tie, order using the cases of the characters. – ypercubeᵀᴹ Feb 28 '17 at 16:31
  • @ypercubeᵀᴹ That makes perfect sense:-) – dmitry Feb 28 '17 at 17:03

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