I have a table that has the following records:
ID | Username | Selected |
----------------------------
1 | JamesC | 1 |
2 | MikeF | 0 |
3 | JamesC | 0 |
I wish to have Selected be true for only 1 row where the username is the same. So for example when I set ID = 3 to be Selected = true I wish to setID =1 to have Selected = false as well as any other ID's with the same username.
Right now i'm doing this,
//set all to 0
update table set selected = 0 where username = '$username'
//set unique row to true
update table set selected = 1 where username = '$username' and ID = '$ID';
Is there a better more concise way of achieving the same effect?
As it was said - not very nice db structure, it is better to have table with unique names and ID of selected item, anyway, you can go with this single query:
update table set selected=IF(id = '$ID', 1, 0) where username = '$username';
also, try a possible faster variant (test both via explain):
update table set selected=IF(id <> '$ID', 0, 1) where username = '$username';
It looks more like optimizing db structure to me. More info needed for concrete answer though, but check this example to see what I'm talking about:
users:
user_id | user_name | selected_character_id | ...other account data
1 | JamesC | 3
2 | MikeF | 2
characters:
character_id | user_id | ...other character data
1 | 1 |
2 | 2 |
3 | 1 |
You will need JOIN tables to retrieve all data for selected character (fast since it operates on unique ids), but get rid of data duplication (and easier switch).
You will always need the second statement, but as you only have one "Selected" row you could use:
update table set selected = 0 where selected = 1
Related
In my table 'users' there are 'friends' ,
Like this :
+----+------+---------+
| id | name | friends |
+----+------+---------+
| 1 | a | 0,1,2 |
| 2 | b | 0,1,3 |
| 3 | c | 0,1 |
+----+------+---------+
How do I use the explode function to get the friends id one by one (not 0,1,2) that are separated by a comma (,) ;
How do I select the id? (Example) :
$sql = Select id from users where id = (exploded)
if (mysql_num_rows($sql) > 0 ) {
$TPL->addbutton('Unfriend');
}else{
$TPL->addbutton('Add as Friend')
}
The solution here is actually a slight change in your database structure. I recommend you create a "many-to-many" relational table containing all of the users friends referenced by user.
+---------+-----------+
| user_id | firend_id |
+---------+-----------+
| 1 | 2 |
| 1 | 3 |
| 1 | 4 |
| 2 | 1 |
| 2 | 5 |
+---------+-----------+
If you are storing lists of values within one field then that is the first sign that your database design is not quite optimal. If you need to search for a numerical value, it'll always be better to place an index on that field to increase efficiency and make the database work for you and not the other way around :)
Then to find out if a user is a friend of someone, you'll query this table -
SELECT * FROM users_friends WHERE
`user_id` = CURRENT_USER AND `friend_id` = OTHER_USER
To get all the friends of a certain user you would do this -
SELECT * FROM users_friends WHERE `user_id` = CURRENT_USER
Just a simple example that will make you clear how to proceed:
// Obtain an array of single values from data like "1,2,3"...
$friends = explode(',', $row['friends']);
Then, back in your query:
// Obtain back data like "1,2,3" from an array of single values...
$frieldslist = implode(',', $friends);
$sql = "SELECT * FROM users WHERE id IN ('" . $frieldslist . "')";
to get an array of if ids from your string explode would be used like this
$my_array = explode("," , $friends);
but you'd probably be better using the mysql IN clause
$sql = "Select id from users where id in (".$row['friends'].")";
Just a quick idea. Change your database's table. It is certain that after a while many problems will arise.
You could have something like this.
id hasfriend
1 2
1 3
2 1 no need to be here (You have this already)
2 4
.....
You can do this by using indexes for uniqueness or programming. You may think of something better. Change your approach to the problem to something like this.
Am storing a string separated using |, which lists the groups allowed, now my issue is if I delete a group than I am not able to remove the ID from that particular field, for example
allowed_group_id
+---------------+
1332|4545|5646|7986
So for example am deleting the group say no 5646, so how do I alter the scripts and remove that particular group from the allowed_group_id in script table?
I recommend taking the entry, exploding it by "|", removing the appropriate entry, imploding it back and updating.
$allowedGroupId = '1332|4545|5646|7986';
$parts = explode('|', $allowedGroupId);
if(($key = array_search($deleteGroup, $allowedGroupId)) !== false) {
unset($allowedGroupId[$key]);
}
$update = " ... "; //update with the new imploded values
Hope it helps
You can try this-
update table tableName set allowed_group_id = REPLACE(allowed_group_id, '5646', '');
Use explode:
$allowed_ids = explode('|', $current_allowed_group_ids);
if($remove_key = array_search($remove_id, $allowed_ids) !== false) {
unset($allowed_ids[$remove_key]);
}
$update_query = 'UPDATE table_name SET allowed_group_id = "'. implode('|', $allowed_ids) .'" WHERE id= ...';
But you might want to alter your database design slightly, creating a pivot table to check for allowed ids. Example:
+------------+
| GROUPS |
+----+-------+
| id | name |
+----+-------+
| 1 | grp_1 |
| 2 | grp_2 |
...
+--------------------+
| ALLOWED_GROUPS |
+--------------------+
| user_id | group_id |
+---------+----------+
| 2 | 1 |
| 2 | 2 |
| 5 | 2 |
...
Using Suresh response and improving it:
UPDATE TABLE tableName SET allowed_group_id = REPLACE(
REPLACE(allowed_group_id, '5646', ''),
'||',
'|');
First you search for '5646' string in allowed_group_id and replace it with empty string ''. Secondly you search and replace two bars from your result '||' with only one bar '|'. This will avoid having '1332|4545||7986' in your allowed_group_id.
Or you should have a table with 2 columns 1 with the id of the action you whant to allow and one with the id of a group.
Whilst the other answers will solve your problem as-is: you might want to consider normalising your database.
For example, if you currently have a table table_name containing id and allowed_group_id, then you would create a new table allowed_group containing multiple rows for each allowed group:
foreign_id | group_id
-----------+---------
1 | 1332
1 | 4545
1 | 5646
1 | 7986
...and so on. Here, foreign_id is the ID of the row in your existing table_name table. Now, instead of your above problem, you can simply DELETE FROM allowed_group WHERE foreign_id = 1 AND groupId = 5646.
This is called putting your data in first normal form.
I have two tables. The first table holds simple user data and has the columns
$username, $text, $image
(this is called "USERDATA").
The second table holds information about which users "follow" other users, which is set up with the columns
$username and $usertheyfollow
(this is called "FOLLOWS").
What I need to do is display the data individually to each user so that it is relevant to them. This means that userABC for instance, needs to be able to view the $text and $image inputs for all of the users whom he/she follows. To do this, I believe I need to write a sql query that involves first checking who the logged in user is (in this case userABC), then selecting all instances of $usertheyfollow on table FOLLOWS that has the corresponding value of "userABC." I then need to go back to my USERDATA table and select $text and $image that has a corresponding value of $usertheyfollow. Then I can just display this using echo command or the like...
How would I write this SQL query? And am I even going about the database architecture the right way?
With tables like so:
userdata table
______________________________
| id | username | text | image |
|------------------------------|
| 1 | jam | text | image |
+------------------------------+
| 2 | sarah | text | image |
+------------------------------+
| 3 | tom | text | image |
+------------------------------+
follows table
_____________________
| userId | userFollow |
|---------------------|
| 1 | 2 |
+---------------------+
| 1 | 3 |
+---------------------+
and use the following SQL:
SELECT userdata.text, userdata.image FROM follows LEFT JOIN userdata ON follows.userFollow = userdata.id WHERE follows.userId = 1
will get all the text and images that user with id '1' follows
As it turns out, neither of these answers were right. #jam6459 was closest.
The correct answer is the following:
SELECT userdata.text, userdata.image, follows.userFollow
FROM userdata
LEFT JOIN follows ON follows.userFollow = userdata.username
WHERE follows.userId = $username
I also found it easier to not have a username correspond to an Id as in jam's table example. This is because the same user can have multiple entries in "USERDATA". I instead used username as the Id.
function get_text_image($username)
{
$sql = "SELECT * FROM USERDATA where username='".$username."'";
$result = mysql_query($sql);
while($row = mysql_fetch_array($result))
{
echo $row['text'];
echo $row['image'];
}
}
function display_data_of_followers($userid)
{
$sql = "SELECT usertheyfollow FROM follow WHERE userid = ".$userid."";
$result = mysql_query($sql);
while($row = mysql_fetch_array($result))
{
get_text_image($row['usertheyfollow']);
}
}
display_data_of_followers($userid);
I have one field in the backend, where I input IDs separated by comma - ID1, ID2, ID3....These are videos in fact. All ids are stored in the field product_videos in the database (as they are typed).
How can I echo these id's on the frontend so they all show for the product?
Storing comma separated data in one data field is a bad idea. It is a real pain to manipulate, so you should really consider revising your db structure.
You haven't shown your data structure, so I'll give a basic example and then explain how it can be improved. My example assumes product_videos is linked to particular users:
table: `users`
| user_id | user_name | product_videos |
|---------|-----------|----------------|
| 1 | User1 | 1,2,3,4,6,7 |
| 2 | User2 | 5 |
You would maybe run a query
SELECT `product_videos` FROM `users` WHERE `user_name` = 'User1'
This would give you one row, with a comma separate value - you would then need to use something like PHP's explode() to convert it into an array and then loop through that array. That is a very bad method (and it will only become harder as you try to do more advanced things).
Instead, it would be easier to use a link table. Imagine:
table: `users`
| user_id | user_name |
|---------|-----------|
| 1 | User1 |
| 2 | User2 |
table: `videos`
| video_id | user_id |
|-----------|---------|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 1 |
| 5 | 2 |
| 6 | 1 |
| 7 | 1 |
In this example, each video is a separate row in a db table (and each video is linked to an existing user). Each row is readily able to be handled independently. This makes it really easy to handle extra data for each video, such as a title, runtime length, date of uploading, etc.
You would then need to run a JOIN query. e.g.
SELECT `videos`.`video_id` FROM `videos`
INNER JOIN `users` ON `users`.`user_id` = `videos`.`user_id`
WHERE `users`.`user_name` = 'User1'
In PHP, you would do something like:
$q = mysql_query("SELECT `videos`.`video_id` FROM `videos` INNER JOIN `users` ON `users`.`user_id` = `videos`.`user_id` WHERE `users`.`user_name` = 'User1'");
while ($row = mysql_fetch_assoc($q)) {
echo "VIDEO ID = " . $row["video_id"] . "<br/>";
}
I have a members table in MySQL
CREATE TABLE `members` (
`id` int(10) unsigned NOT NULL auto_increment,
`name` varchar(65) collate utf8_unicode_ci NOT NULL,
`order` tinyint(3) unsigned NOT NULL default '0',
PRIMARY KEY (`id`)
) ENGINE=InnoDB;
And I would like to let users order the members how they like.
I'm storing the order in order column.
I'm wondering how to insert new user to be added to the bottom of the list.
This is what I have today:
$db->query('insert into members VALUES (0, "new member", 0)');
$lastId = $db->lastInsertId();
$maxOrder = $db->fetchAll('select MAX(`order`) max_order FROM members');
$db->query('update members
SET
`order` = ?
WHERE
id = ?',
array(
$maxOrder[0]['max_order'] + 1,
$lastId
));
But that's not really precise while when there are several users adding new members at the same time, it might happen the MAX(order) will return the same values.
How do you handle such cases?
You can do the SELECT as part of the INSERT, such as:
INSERT INTO members SELECT 0, "new member", max(`order`)+1 FROM members;
Keep in mind that you are going to want to have an index on the order column to make the SELECT part optimized.
In addition, you might want to reconsider the tinyint for order, unless you only expect to only have 255 orders ever.
Also order is a reserved word and you will always need to write it as `order`, so you might consider renaming that column as well.
Since you already automatically increment the id for each new member, you can order by id.
I am not sure I understand. If each user wants a different order how will you store individual user preferences in one single field in the "members" table?
Usually you just let users to order based on the natural order of the fields. What is the purpose of the order field?
Usually I make all my select statements order by "order, name"; Then I always insert the same value for Order (either 0 or 9999999 depending on if I want them first or last). Then the user can reorder however they like.
InnoDB supports transactions. Before the insert do a 'begin' statement and when your finished do a commit. See this article for an explanation of transactions in mySql.
What you could do is create a table with keys (member_id,position) that maps to another member_id. Then you can store the ordering in that table separate from the member list itself. (Each member retains their own list ordering, which is what I assume you want...?)
Supposing that you have a member table like this:
+-----------+--------------+
| member_id | name |
+-----------+--------------+
| 1 | John Smith |
| 2 | John Doe |
| 3 | John Johnson |
| 4 | Sue Someone |
+-----------+--------------+
Then, you could have an ordering table like this:
+---------------+----------+-----------------+
| member_id_key | position | member_id_value |
+---------------+----------+-----------------+
| 1 | 1 | 4 |
| 1 | 2 | 1 |
| 1 | 3 | 3 |
| 1 | 4 | 2 |
| 2 | 2 | 1 |
| 2 | 3 | 2 |
+---------------+----------+-----------------+
You can select the member list given the stored order by using an inner join. For example:
SELECT name
FROM members inner join orderings
ON members.member_id = orderings.member_id_value
WHERE orderings.member_id_key = <ID for member you want to lookup>
ORDER BY position;
As an example, the result of running this query for John Smith's list (ie, WHERE member_id_key = 1) would be:
+--------------+
| name |
+--------------+
| Sue Someone |
| John Smith |
| John Johnson |
| John Doe |
+--------------+
You can calculate position for adding to the bottom of the list by adding one to the max position value for a given id.