3 ms·

But shouldn't that be a separate field then?

• mattashii 3y ago
  The logistics of combining fields in indexes and identifiers is relatively complex, while the logistics of indexing a single field is comparatively trivial. This is also why you don't ship timestamps using separate fields for second/minute/hour/day/month/year, but a single ISO-string or UNIX timestamp as representation: it makes querying and interpreting the value more consistent.
  • frankreyes 3y ago
    Create a new column with an MD5 hash of the other columns. Easy. /s
    • rvnx 3y ago
      This is how it works, except it's not MD5 but a less-costly hash function
      • eru 3y ago
        MD5 is a useless hash function these days. It's not cryptographically secure (anymore). And there are cheaper non-cryptographically secure hash functions.
  • btilly 3y ago
    Disagree on "relatively complex". create index on $table ($field1, $field2); Seems pretty simple to me.
    • mattashii 3y ago
      It is noy just the DDL of the primary table that needs to care about it, but also all foreign keys, DML, queries, APIs accessing the data, etc. Storing that UUIDv7 is likely going to be cheaper than pushing the cost of keeping a composite identity onto other components and systems that work with that data.
      • btilly 3y ago
        Well, that depends on how you manage it. An ORM will find it trivial. Custom SQL, not always so much. That said, PostgreSQL offers https://www.postgresql.org/docs/current/rowtypes.html https://www.postgresql.org/docs/current/rowtypes.html which gives you the best of both worlds. A single field which contains 2 fields that can later be extracted. So everywhere you can write a single field for joins, etc. But then when you need it broken out...
• madsbuch 3y ago
  I am curios about this, and might be misunderstanding what you mean. Can you layout a demo architecture where you use multiple keys like you propose?
  • junon 3y ago
    There are many DBMSes that combine columns into a singular primary key. Performance tradeoffs vary, especially when it comes to indexing.
  • e12e 3y ago
    Any pure relational database design will eschew surrogate keys - most real-world systems will (should) add them back - because a surprising number of good natural keys end up changing (names change, phone numbers change, emails change, twitter handles become irrelevant/disappear, location of birth may change subject to geographic regions changing size...). And on top of all that, there are efficiency concerns. That said, at least for join tables AFAIK - there aren't often a need for row IDs beyond the involved foreign keys - unless you need to add meta data from other relations/tables...
    • TRiG_Ireland 3y ago
      > location of birth may change My British passport says I was born in Birr; my Irish passport says I was born in Galway. These are both correct, because they are answering different questions. (I was born in the town of Ballinasloe in County Galway, but my mother's place of residence at the time of my birth was the town of Birr in County Offaly.)
      • pc86 3y ago
        So British place of birth means "mother's residence" and not place of birth?
        • rvnx 3y ago
          Official guidances here: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1113426/Place_and_country_of_birth_V18.pdf https://assets.publishing.service.gov.uk/government/uploads/... Could maybe be just a mistake when doing the UK registration ? It's an easy fix if wanted.
• dtech 3y ago
  But then you have 2 identifiers which complicates everything.