Fix mysql fingerprint for ORDER BY FIELD()

Previously we had different fingerprints depending on the number of ids
given in FIELD().

Author: charkost

Diff for: lib/prosopite.rb

@@ -179,6 +179,8 @@ def mysql_fingerprint(query)
 
       query.gsub!(/\b(in|values?)(?:[\s,]*\([\s?,]*\))+/, "\\1(?+)")
 
+      query.gsub!(/(?<!\w)field\s*\(\s*(\S+)\s*,\s*(\?+)(?:\s*,\s*\?+)*\)/, 'field(\1, \2+)')
+
       query.gsub!(/\b(select\s.*?)(?:(\sunion(?:\sall)?)\s\1)+/, "\\1 /*repeat\\2*/")
 
       query.gsub!(/\blimit \?(?:, ?\?| offset \?)/, "limit ?")

Diff for: test/test_mysql_fingerprint.rb

@@ -280,6 +280,10 @@ def test_order_by_clauses
       Prosopite.mysql_fingerprint("SELECT * from a_table ORDER BY foo ASC, bar DESC, baz, quux ASC"),
       "select * from a_table order by foo, bar desc, baz, quux"
     )
+    assert_equal(
+      Prosopite.mysql_fingerprint("SELECT * from a_table ORDER BY FIELD(id, 1, 2, 3, 4)"),
+      "select * from a_table order by field(id, ?+)"
+    )
   end
 
   def test_call_procedures