Phoenix Kiula wrote:

Ok, I've hit a snag about this index. I think it's to do with how my
regex is structured. Basically this column can have either IP
addresses, or alphanumeric user IDs. If it is not an IP address, it is
a registered user ID. What is the best way of ascertaining that a
column value is *not* an IP address?

I tried this:

select * from trader where trader_id !~ '[0-9]+\.[0-9]+\.[0-9]+\.';

And this works, but I wonder if a partial index on a negative
condition ("!~") will be slower than a positive condition?

To be honest, I'd probably just have a separate column "uid_type", set it when creating the user and then just have a partial index WHERE uid_type='IP'

--
  Richard Huxton
  Archonet Ltd

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TIP 9: In versions below 8.0, the planner will ignore your desire to
      choose an index scan if your joining column's datatypes do not
      match

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