PostgreSQL Functions – Set Default Values and Argument Dependencies

default valuefunctionspostgresql

I would like to write a function with two arguments, which would have dependency. Something like this:

    CREATE OR REPLACE FUNCTION years_compare(
        IN year1 integer DEFAULT date_part('year'::text, ('now'::text)::date),
        IN year2 integer DEFAULT year1 - 1)

...

When I call a function years_compare(2019), the second argument would have a value 2018. But how can I write a default value for the second argument?

Best Answer

CREATE OR REPLACE FUNCTION years_compare( IN year1 integer DEFAULT NULL,
                                          IN year2 integer DEFAULT NULL )

    year1 = COALESCE(year1, date_part('year'::text, ('now'::text)::date));
    year2 = COALESCE(year2, year1 - 1);
-- ...

Related Solutions

Oracle extract slow function call from a WHERE clause

The second form of your query will work if you make your mark your function as deterministic, meaning that for a given set of input values, it will always return the same result.
With that set, Oracle will only run the conversion once for each parameters in the where clause rather than for every row.

With this:

CREATE OR REPLACE FUNCTION TO_MINUTE_D (DATE_IN IN DATE)
RETURN NUMBER DETERMINISTIC AS
BEGIN
  /* Minute 0 = 12/30/1899 12:00am */
  RETURN
    (TRUNC(DATE_IN, 'DD') - TO_DATE('12/30/1899', 'MM/DD/YYYY')) * 1440 +
    TO_NUMBER(TO_CHAR(DATE_IN, 'HH24'))  * 60 +
    TO_NUMBER(TO_CHAR(DATE_IN, 'MI'));
END TO_MINUTE_D;
/

On a table filled with a large bunch of dummy rows (increasing ints), I get the following timings consistently:

SQL> SELECT * FROM MY_TABLE
WHERE START_MINUTE < TO_MINUTE(TO_DATE('2013-01-31', 'YYYY-MM-DD'))
AND STOP_MINUTE > TO_MINUTE(TO_DATE('2013-01-01', 'YYYY-MM-DD'));

no rows selected

Elapsed: 00:00:12.69

versus deterministic-annotated function:

SQL> SELECT * FROM MY_TABLE
     WHERE START_MINUTE < TO_MINUTE_D(TO_DATE('2013-01-31', 'YYYY-MM-DD'))
     AND STOP_MINUTE > TO_MINUTE_D(TO_DATE('2013-01-01', 'YYYY-MM-DD')); 

no rows selected

Elapsed: 00:00:00.07

You should get very close to what you have with the values plugged in directly, and indexes on those columns can be used as if you'd plugged in literals.

(Putting the conversion function on the start|stop_minute columns isn't a good idea in general as you've discovered, unless you have a function-based index on those that matches exactly.)

MySQL – Default Value for Microtime Column

You could format it with UNIX_TIMESTAMP like below:

mysql> SELECT UNIX_TIMESTAMP(NOW(6));
+------------------------+
| UNIX_TIMESTAMP(NOW(6)) |
+------------------------+
|      1442068528.543100 |
+------------------------+
1 row in set (0,00 sec)

mysql>

You can find any others date and time functions here. You could add a trigger and if you want a default value for your decimal(16, 6) microtime, use BEFORE INSERT and replace your NEW.bigintvalue=UNIX_TIMESTAMP(NOW(6));.

Example:

mysql> CREATE TABLE `test`.`test1` (
    ->   `id` INT NOT NULL AUTO_INCREMENT,
    ->   `time` DECIMAL(16, 6) NULL,
    ->   PRIMARY KEY (`id`));
Query OK, 0 rows affected (0.01 sec)

mysql> 
mysql> DELIMITER //
mysql> CREATE DEFINER=`root`@`localhost` TRIGGER `test`.`test1_BEFORE_INSERT` BEFORE INSERT ON `test1` FOR EACH ROW
    -> BEGIN
    -> SET NEW.time=UNIX_TIMESTAMP(NOW(6));
    -> END
    -> //
Query OK, 0 rows affected (0.00 sec)

mysql> DELIMITER ;
mysql> 
mysql> # Adding 1 into id field
mysql> INSERT INTO `test`.`test1` (`id`) VALUES ('1');
Query OK, 1 row affected (0.00 sec)

mysql> select * from test.test1;
+----+-------------------+
| id | time              |
+----+-------------------+
|  1 | 1442069359.675330 |
+----+-------------------+
1 row in set (0.00 sec)

mysql>

Best Answer

Related Solutions

Oracle extract slow function call from a WHERE clause

MySQL – Default Value for Microtime Column

Example:

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