Generate short, random, textual IDs

Couple of people asked, on irc, about how to generate unique, short, ids for rows.

Since I wrote code for this for explain.depesz.com, I figured that instead of pointing to sources, and letting everyone to extract the functions, I will, instead, write a set of functions that what is needed in reusable way.

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“= 123” vs. “= ‘depesz'”. What is faster?

There is this idea that normal form in databases require you to use integer, auto incrementing, primary keys.

The idea was discussed by many people, I will just point you to series of three blog posts on the subject by Josh Berkus ( part 1, 2 and 3, and reprise).

One of the points that proponents of surrogate keys (i.e. those based on integer and sequences) raise is that comparing integers is faster than comparing texts. So,

SELECT * FROM users WHERE id = 123

is faster than

SELECT * FROM users WHERE username = 'depesz'

Is it?

Continue reading “= 123" vs. “= ‘depesz'". What is faster?

Waiting for 9.1 – Add UNIQUE/PRIMARY KEY with index

On 25th of January, Tom Lane committed patch:

Implement ALTER TABLE ADD UNIQUE/PRIMARY KEY USING INDEX.
 
This feature allows a UNIQUE OR pkey CONSTRAINT TO be created USING an
already-existing UNIQUE INDEX.  While the CONSTRAINT isn't very
functionally different from the bare index, it's nice TO be able TO do that
FOR documentation purposes.  The main advantage OVER just issuing a plain
ALTER TABLE ADD UNIQUE/PRIMARY KEY IS that the INDEX can be created WITH
CREATE INDEX CONCURRENTLY, so that there IS NOT a long INTERVAL WHERE the
TABLE IS locked against updates.
 
ON the way, refactor SOME OF the code IN DefineIndex() AND index_create()
so that we don't have to pass through those functions in order to create
the index constraint's catalog entries.  Also, IN parse_utilcmd.c, pass
around the ParseState pointer IN struct CreateStmtContext TO save ON
notation, AND ADD error location pointers TO SOME error reports that didn't
have one before.
 
Gurjeet Singh, reviewed by Steve Singer and Tom Lane

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Waiting for 9.1 – Recognize functional dependency on primary keys.

Yesterday (August, 7th), Tom Lane committed:

Log Message:
-----------
Recognize functional dependency on primary keys.  This allows a table's
other columns to be referenced without listing them in GROUP BY, so long as
the primary key column(s) are listed in GROUP BY.
 
Eventually we should also allow functional dependency on a UNIQUE constraint
when the columns are marked NOT NULL, but that has to wait until NOT NULL
constraints are represented in pg_constraint, because we need to have
pg_constraint OIDs for all the conditions needed to ensure functional
dependency.
 
Peter Eisentraut, reviewed by Alex Hunsaker and Tom Lane

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Waiting for 8.5 – deferrable uniqueness

On 29th of July ( I know, there is a long backlog in waiting for 8.5 series. I'm working on it :), Tom Lane committed patch by Dean Rasheed:

Support deferrable uniqueness constraints.
 
The current implementation fires an AFTER ROW trigger for each tuple that
looks like it might be non-unique according to the index contents at the
time of insertion.  This works well as long as there aren't many conflicts,
but won't scale to massive unique-key reassignments.  Improving that case
is a TODO item.
 
Dean Rasheed

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