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 Data Definition Language (DDL)Procedural SQL (PSQL) 

QUARTER added to EXTRACT, FIRST_DAY and LAST_DAY

The scalar functions EXTRACT, FIRST_DAY and LAST_DAY now support the date part QUARTER.

Example
select
  extract(quarter from date '2023-09-21') as Q,
  first_day(of quarter from date '2023-09-21') as Q_START,
  last_day(of quarter from date '2023-09-21') as Q_END
from rdb$database;

      Q     Q_START       Q_END
======= =========== ===========
      3 2023-07-01  2023-09-30

SKIP LOCKED clause

Adriano dos Santos Fernandes

Tracker ticket: #7350

SKIP LOCKED can be used with SELECT …​ WITH LOCK, UPDATE and DELETE statements.It makes the engine skip records locked by other transactions instead of waiting on them or raise conflict errors.

This is very useful to implement work queues where one or more processes post work to a table and issue an event, while workers listen for events and read/delete items from the table.Using SKIP LOCKED multiple workers can get exclusive work items from the table without conflicts.

Syntax
SELECT
  [FIRST ...]
  [SKIP ...]
  FROM <sometable>
  [WHERE ...]
  [PLAN ...]
  [ORDER BY ...]
  [{ ROWS ... } | {OFFSET ...} | {FETCH ...}]
  [FOR UPDATE [OF ...]]
  [WITH LOCK [SKIP LOCKED]]

UPDATE <sometable>
  SET ...
  [WHERE ...]
  [PLAN ...]
  [ORDER BY ...]
  [ROWS ...]
  [SKIP LOCKED]
  [RETURNING ...]

DELETE FROM <sometable>
  [WHERE ...]
  [PLAN ...]
  [ORDER BY ...]
  [ROWS ...]
  [SKIP LOCKED]
  [RETURNING ...]
Note

If a statement has both SKIP LOCKED and OFFSET/SKIP/ROWS subclauses, locked rows may be skipped before OFFSET/SKIP/ROWS subclause can account for them, thus skipping more rows than specified in OFFSET/SKIP/ROWS.

Examples:

  • Prepare metadata

    create table emails_queue (
    subject varchar(60) not null,
    text blob sub_type text not null
);

set term !;

create trigger emails_queue_ins after insert on emails_queue
as
begin
    post_event('EMAILS_QUEUE');
end!

set term ;!

  • Sender application or routine

    insert into emails_queue (subject, text)
  values ('E-mail subject', 'E-mail text...');
commit;

  • Client application

    -- Client application can listen to event `EMAILS_QUEUE` to actually send e-mails using this query:

delete from emails_queue
  rows 10
  skip locked
  returning subject, text;

    More than one instance of the application may be running, for example to load balance work.