get columns default values as they are a row of a resultset - php

Question

is there a way to get default values of columns as they are a row of a resultset?
`id` mediumint(9) NOT NULL AUTO_INCREMENT,
`state` tinyint(2) NOT NULL DEFAULT '22',
`pubdate` datetime NOT NULL DEFAULT '2012-01-01 00:00:00',
for instance a table like this should return this record:
id->NULL (?)
state->22
pubdate->2012-01-01 00:00:00
in practice, when some user opens edit.php?id=44 he will get the row 44 (update mode), but if he opens edit.php?id=0 (insert mode) I want that the fields contain default values as place holders
thank you in advance

Answer 1

There is a DEFAULT function
SELECT DEFAULT( id ) , DEFAULT( EXAMPLE ) FROM test LIMIT 1
With above query, it seems that you need to have atleast one record in the table as it returns no records otherwise. For current timestamp, it return a timestamp formatted string of 0s.

Answer 2

Sure, using the information_schema database (which stores all the information about your database structure), you can do something like:
SELECT
COLUMN_NAME,
COLUMN_DEFAULT
TABLE_NAME
FROM information_schema.COLUMNS
WHERE
TABLE_NAME='your_table_name'
AND TABLE_SCHEMA='your_database_name'
If you have a limited number of columns, you can collect them into a row using a construct like:
SELECT
id.defaultval AS id_default,
state.defaultval AS state_default,
pubdate.defaultval AS pubdate_default
FROM
(SELECT TABLE_NAME, COLUMN_DEFAULT AS defaultval FROM information_schema.COLUMNS WHERE TABLE_NAME='your_table' AND TABLE_SCHEMA='your_database' AND COLUMN_NAME='id') id
JOIN (SELECT COLUMN_DEFAULT AS defaultval FROM information_schema.COLUMNS WHERE TABLE_NAME='your_table' AND TABLE_SCHEMA='your_database' AND COLUMN_NAME='state') state ON id.TABLE_NAME = state.TABLE_NAME
JOIN (SELECT COLUMN_DEFAULT AS defaultval FROM information_schema.COLUMNS WHERE TABLE_NAME='your_table' AND TABLE_SCHEMA='your_database' AND COLUMN_NAME='pubdate') pubdate ON id.TABLE_NAME = pubdate.TABLE_NAME

Answer 3

Use DESCRIBE http://dev.mysql.com/doc/refman/5.0/en/describe.html
DESCRIBE sometable [somefield]
Here is php example for single field:
$resource = mysql_query("DESCRIBE sometable somefield");
$schema = mysql_fetch_assoc($resource);
$default = $schema['default'];
And here is the php example for few fields:
$resource = mysql_query("DESCRIBE sometable");
while ($schema = mysql_fetch_assoc($resource)) {
$default_list[$schema['Field']] = $schema['Default'];
}

Answer 4

I see no use for such a behavior and find it wrong.
It is not convenient to use. Imagine I want to enter my own state value. I'd have to delete default 22 first.
Even worse with date. Instead of setting current datetime, you are going to make me edit whole date. Why?
And for the id it is just impossible.
Why can't you just check the input fields and if empty - not to insert at all, letting database set these defaults
You just overthinked it, I believe.