Ansi SQL – Creating Auto Numbered Column

auto-incrementsql-standard

Is there an ANSI standard for auto-numbered columns.

Currently, we have a choice of SERIAL, AUTOINCREMENT, AUTO_INCREMENT, IDENTITY() and good old NEXTVAL() among others.

I read somewhere that there is a new standard using IDENTITY which I know that Oracle has recently implemented. I know that Oracle is hardly the last word on standards.

If there is a standard, then it’s a long time coming.

Best Answer

Yes there is, and it's definitely not "a new standard". It's been in the SQL standard since SQL:2003

The definition is:

<identity column specification> ::=
  GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY
    [ <left paren> <common sequence generator options> <right paren> ]

The optional part with the sequence generator options lets you define the characteristics of the underlying sequence (=generator), you could do something like:

id integer GENERATED ALWAYS AS IDENTITY (start with 42 increment by 10 cycle)

This syntax is supported (at least) by PostgreSQL 10, Oracle 12.1, DB2, Apache Derby, HSQLDB, Firebird and NuoDB.

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SQL Standard – Why ANSI SQL Defines SUM(no rows) as NULL

I'm afraid that the reason is simply that the rules were set in an adhoc fashion (like quite many other "features" of the ISO SQL standard) at a time when SQL aggregations and their connection with mathematics were less understood than they are now (*).

It's just one of the extremely many inconsistencies in the SQL language. They make the language harder to teach, harder to learn, harder to understand, harder to use, harder to whatever you want, but that's just the way things are. The rules cannot be changed "cold" and "just like that", for obvious reasons of backward compatibility (If the ISO committee publishes a final version of the standard, and vendors then set out to implement that standard, then those vendors will not appreciate it very much if in a subsequent version, the rules are changed such that existing (compliant) implementations of the former version of the standard "automatically fail to comply" the new version ...)

(*) It is now better understood that aggregations over an empty set behave more consistently if they systematically return the identity value (= what you call the 'neutral element') of the underlying binary operator at hand. That underlying binary operator for COUNT and SUM is addition, and its identity value is zero. For MIN and MAX, that identity value is the highest and lowest value of the type at hand, respectively, if the concerned types are finite. Cases like averaging, harmonic means, medians, etc. are extremely intricate and exotic in this respect, though.

ANSI/ISO plans for LIMIT standardization

The latest draft SQL standard that I could find on the internet (dated 21/12/2011) has the following available for use in a query expression:

<result offset clause> ::=
    OFFSET <offset row count> { ROW | ROWS }

<fetch first clause> ::=
    FETCH { FIRST | NEXT } [ <fetch first quantity> ] { ROW | ROWS } { ONLY | WITH TIES }

Best Answer

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