I am currently learning the basics of creating a database and doing some line of data analysis. i have been struggling to understand how to 'start coding'
so i finally decided to come up with a simple diary project to kick start my coding life.
Here is what i have so far, in terms of python so far nothing except i managed to link python and mysql.
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| diary |
| mysql |
| performance_schema |
| sakila |
| sys |
| world |
+--------------------+
7 rows in set (0.00 sec)
mysql> desc diary;
+---------------+--------------+------+-----+-------------------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------------+--------------+------+-----+-------------------+-------+
| TASK_COMMENTS | varchar(255) | YES | | NULL | |
| TASK | varchar(55) | NO | | NULL | |
| TS | timestamp | NO | | CURRENT_TIMESTAMP | |
+---------------+--------------+------+-----+-------------------+-------+
3 rows in set (0.00 sec)
mysql> select * from diary;
+---------------+---------------+---------------------+
| TASK_COMMENTS | TASK | TS |
+---------------+---------------+---------------------+
| NULL | Food Shopping | 2016-12-25 18:53:32 |
+---------------+---------------+---------------------+
1 row in set (0.00 sec)
here is the question finally:): Is it correct if i make the time stamp a primary key or is it more 'database error-free' to create an actual id instead of using automated timestamp as the pk?
also i am trying to make TASK_COMMENTS field not null aswell but i get this:
mysql> ALTER TABLE Diary MODIFY COLUMN TASK_COMMENTS VARCHAR(255) NOT NULL;
ERROR 1138 (22004): Invalid use of NULL value
Thank you for helping.
You can't alter the default value of a column to NOT NULL if a NULL value already exists. Either delete the row, or set it to something, then you can alter the column.
Using a timestamp is not a good idea for a primary key because it is very possible to get duplicate values. It's also easy not to, but it's just not a good idea. Use an id column, set the PK, and typically one would give it AUTO INCREMENT to ensure no duplicates.
Related
I have made the following table in MySQL:
mysql> use test;
Database changed
mysql> desc NeoTec_test;
+-------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------------+-------------+------+-----+---------+-------+
| Product_Key | varchar(10) | NO | PRI | NULL | |
| Validation | date | YES | | NULL | |
| Expiry | date | YES | | NULL | |
+-------------+-------------+------+-----+---------+-------+
3 rows in set (0.03 sec)
mysql> select * from NeoTec_test;
+-------------+------------+------------+
| Product_Key | Validation | Expiry |
+-------------+------------+------------+
| GF427DHH5 | 2017-11-16 | 2017-11-17 |
| GFHJV75HG | 2017-11-16 | 2017-11-18 |
| GFJYFRTV5 | 2017-11-16 | 2017-11-20 |
+-------------+------------+------------+
3 rows in set (0.00 sec)
Now coming to the point, I need some help with a part of my project. I want MySQL to automatically delete the Product keys that have expired, i.e., I want to get the product keys deleted automatically on their expiry dates given under the "Expiry" Column of the table. How can I do so? I am a total newbie to MySQL events so I would appreciate the full code... Thank you! :-)
Earlier research I did was not fruitful, but I did found this, which was half helpful...:
How to delete a MySQL record after a certain time
You can use event scheduler to perform the task like below:
DELIMITER //
CREATE EVENT eventName
ON SCHEDULE EVERY 1 WEEK
STARTS 'Some Date to start'
ENDS 'End date If any'
DO
BEGIN
DELETE FROM NeoTec_test WHERE NOW() > Expiry
END//
DELIMITER ;
Thete is no functionality in mysql to automatically delete a record. You need to trigger the deletion either through a scheduler (mysql's as shown in the question you found, or an external scheduler such as cron), or via a database trigger.
The latter one is probably an overkill.
I would use a scheduler set to a convenient interval based on your business requirements to clean up the table.
For some reasons it seems that the rows are not being updated. Any idea why this would happen ?
UPDATE hts SET assigned='1' AND Owner='ms' WHERE hid='217477'
Query OK, 0 rows affected (0.16 sec)
Rows matched: 1 Changed: 0 Warnings: 0
select assigned, Owner from hts where hid='217477';
+----------+-------+
| assigned | Owner |
+----------+-------+
| NULL | NULL |
+----------+-------+
Show columns from hts
+------------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------+--------------+------+-----+---------+-------+
| hid | varchar(25) | YES | UNI | NULL | |
| assigned | int(11) | NO | | 0 | |
| Owner | varchar(10) | YES | | NULL | |
+------------+--------------+------+-----+---------+-------+
two things you can try..
first try removing the AND from the SET.. usually you do that with a comma..
UPDATE hts SET assigned=1, Owner='ms' WHERE hid='217477'
second try removing the quotes form the hid if it is an INT and not a VARCHAR
UPDATE hts SET assigned=1, Owner='ms' WHERE hid=217477
not sure why you are storing integers as strings.. when in doubt you should ALWAYS store data by its intended datatype.
RECOMMENDATION: change the datatypes if they are varchar to int. your update would look like this.
UPDATE hts SET assigned=1, Owner='ms' WHERE hid=217477
assigned should be integer as well as hid
Further to my previous question (qv) ...
I have already created the table(s) and populated with data. How do I set the prefix length to a very large value or remove it all togther, so that I don't have this problem? There will never be more than a few thousand rows and only this applciation is running on a dedicated PC, so performance is not an issue.
Solution, please for either PhpMyAdmin, or just MySQL command line.
Update: Can I just delete this index (or make it infinitely long)?
Hmmm, I would prefer to keep the unique index if I can. So, how to make it infinitely long?
Or should I redefine my text fields to be var_char with a limit to the length? (I do know the max possible lngth of the primary key)
mysql> describe tagged_chemicals;
+-------------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------------+---------+------+-----+---------+-------+
| bar_code | text | NO | | NULL | |
| rfid_tag | text | NO | UNI | NULL | |
| checked_out | char(1) | NO | | N | |
+-------------+---------+------+-----+---------+-------+
3 rows in set (0.04 sec)
It'll probably be something like
CREATE INDEX part_of_name ON customer (name(10));
from create index documentation http://dev.mysql.com/doc/refman/5.0/en/create-index.html
where in your case the rfid_tag is length 20.
For a preferences module I have "system defaults", and "user preferences".
If there is no personal/user preference stored, then use the system default values instead.
Here is my system preferences table:
mysql> desc rbl;
+-------------+---------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------------+---------------------+------+-----+---------+-------+
| id | varchar(3) | NO | PRI | | |
| rbl_url | varchar(100) | NO | | | |
| description | varchar(100) | NO | | | |
| is_default | tinyint(1) unsigned | YES | | 1 | |
+-------------+---------------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
Example data from system prefs:
mysql> select * from rbl;
+----+----------------------+------------------------------+------------+
| id | rbl_url | description | is_default |
+----+----------------------+------------------------------+------------+
| 1 | sbl-xbl.spamhaus.org | Spamhaus SBL-XBL | 1 |
| 2 | pbl.spamhaus.org | Spamhaus PBL | 1 |
| 3 | bl.spamcop.net | Spamcop Blacklist | 1 |
| 4 | rbl.example.com | Example RBL - not functional | 0 |
+----+----------------------+------------------------------+------------+
... and Query for system defaults:
mysql> SELECT rbl_url FROM rbl WHERE is_default='1';
+----------------------+
| rbl_url |
+----------------------+
| sbl-xbl.spamhaus.org |
| pbl.spamhaus.org |
| bl.spamcop.net |
+----------------------+
3 rows in set (0.01 sec)
So far so good.
OK. Now I need a user preferences table, and I came up with this:
mysql> desc rbl_pref;
+-----------+-----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+-----------------------+------+-----+---------+----------------+
| id | mediumint(8) unsigned | NO | PRI | NULL | auto_increment |
| domain_id | mediumint(8) unsigned | NO | | NULL | |
| rbl_id | tinyint(1) unsigned | NO | | NULL | |
+-----------+-----------------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
(FYI - A "user" is represented by "domain_id". )
Let's view the preferences of a specific user who has personalized preferences saved:
mysql> select * from rbl_pref where domain_id='2277';
+----+-----------+--------+
| id | domain_id | rbl_id |
+----+-----------+--------+
| 4 | 2277 | 1 |
| 5 | 2277 | 2 |
| 6 | 2277 | 4 |
+----+-----------+--------+
3 rows in set (0.00 sec)
... again, but in a simpler format:
mysql> SELECT rbl.rbl_url FROM rbl_pref,rbl
WHERE rbl_pref.rbl_id=rbl.id AND domain_id='2277';
+----------------------+
| rbl_url |
+----------------------+
| sbl-xbl.spamhaus.org |
| pbl.spamhaus.org |
| rbl.example.com |
+----------------------+
3 rows in set (0.00 sec)
.. so far so good. If a user has stored a preference, a result is found.
The problem example now is, user 1999 has no custom preferences.
In place of the "Empty set" result, I want the system defaults.
mysql> SELECT rbl.rbl_url FROM rbl_pref,rbl
WHERE rbl_pref.rbl_id=rbl.id AND domain_id='1999';
Empty set (0.00 sec)
I was excited to find a very similar question:
mysql if row doesn't exist, grab default value
However after a couple of days trial and error and documentation review, I could not translate that answer over to here.
Like the above question, this must be done as a single MySQL query. I am not actually making this query from PHP, but from Exim macros (and it is a very picky language... best to feed it "one liners" as variable assignments, as I try to do here.. )
UPDATE: Tried one type of a UNION query suggested by #Biff McGriff, below. The table did not display in my comment reply, so here it is again:
mysql> SELECT rbl.rbl_url FROM rbl_pref,rbl
WHERE rbl_pref.rbl_id=rbl.id AND domain_id='2277'
UNION SELECT rbl_url FROM rbl WHERE is_default='1';
+----------------------+
| rbl_url |
+----------------------+
| sbl-xbl.spamhaus.org |
| pbl.spamhaus.org |
| rbl.example.com |
| bl.spamcop.net |
+----------------------+
4 rows in set (0.00 sec)
As you can see above, user 2277 did not opt in to rbl_id 3 (bl.spamcop.net), but that's showing up anyways.
What my UNION query seems to be doing is combining the result set. So user_pref acts as "in addition to" global defaults, and I was assuming/expecting I would get a result set matching either half of the query.
So my question now is, is it better (or possible, how) to solve this as "either result set" (either subquery on either side of the UNION)? OR do I really need a new field on rbl_pref, called for example "enabled". The latter seems to be more correct - that I need something in rbl_pref to explicitly designate opt-in or opt-out (other than the implicit "that pref is not here - no rbl_id=3 - in the over ridden user result SET")
UPDATE: All set, thanks #Imre L, and everyone else. I learned something through this example.
You should be able to use a left join and then coalesce the user's field with the default field.
NOTE: you have to enter the domain_id in two places.
SELECT rbl.rbl_url FROM rbl
JOIN rbl_pref ON rbl_pref.rbl_id=rbl.id AND domain_id=2277
UNION
SELECT rbl.rbl_url FROM rbl
WHERE rbl.is_default
AND NOT EXISTS (SELECT 1 FROM rbl_pref WHERE domain_id=2277 LIMIT 1)
;
Now one or the other side of UNION will be optimized away with impossible where
You also should not use varchar(3) for rbl.id but some sort of integer
and preferable same type as rbl_pref.rbl_id for which tinyint is too tiny
and when you compare integers fields in sql code domain_id='2277' you should not use ' or " around constants integers.
You can get away whith it mostly but sometimes it may confuse mysql optimizer.
Also for optimal performance and consistency i suggest you the add the index:
ALTER TABLE rbl_pref
ADD UNIQUE INDEX ux_domain_rbl (domain_id, rbl_id);
Is there any way to convert the warning that MySQL is issuing about an invalid datetime into a hard error? I've tried using SET sql_mode='TRADITIONAL'; which apparently is supposed to turn (some) things that are warnings into errors, but it does not have any effect here. This is MySQL 5.1.56. Something that works on a session-level would be ideal, but I'll take what I can get.
mysql> describe test_table2;
+----------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| value | int(11) | YES | | NULL | |
| name | varchar(16) | YES | | NULL | |
| sometime | datetime | YES | | NULL | |
+----------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
mysql> select * from test_table2;
+-------+-------+---------------------+
| value | name | sometime |
+-------+-------+---------------------+
| 1 | one | 2002-09-01 10:00:00 |
| 2 | two | 2002-09-02 11:00:00 |
| 3 | three | 2002-09-03 12:00:00 |
| 4 | four | 2002-01-04 13:00:00 |
| 5 | five | 2002-01-05 14:00:00 |
+-------+-------+---------------------+
5 rows in set (0.00 sec)
mysql> select * from test_table2 where sometime = 'foo';
Empty set, 2 warnings (0.00 sec)
Warning (Code 1292): Incorrect datetime value: 'foo' for column 'sometime' at row 1
Warning (Code 1292): Incorrect datetime value: 'foo' for column 'sometime' at row 1
With SET sql_mode='TRADITIONAL', doing an INSERT with an invalid date causes an error, but doing a SELECT with an invalid date still causes a warning. You can trigger the error by passing the (possibly invalid) date value to this query first:
CREATE TEMPORARY TABLE IF NOT EXISTS date_guard (date DATE) SELECT 'foo' AS date;
where 'foo' is the date value you want to validate.
Who is supposed to see the error?
If this is a fixed string 'foo' just try converting 'foo' to a date and see if you can a valid result (i.e. not 00-00-000). Do a pre-query to check the validity of the date, and then continue after.
I have not been able to make MySQL give an error in this case (or even convert the invalid date to a NULL - it insists on making it 00-00-0000).