I need to return a single row with some datas taken from some tables not related each others.
So, for example, my actual queries are these (I done it trought a PHP script) :
$query=mysql_query("SELECT trackid FROM tracklist WHERE usersub='".$_SESSION['nickname']."'",$mydb);
echo mysql_num_rows($query);
$query=mysql_query("SELECT trackid FROM comments WHERE usercom='".$_SESSION['nickname']."'",$mydb);
echo mysql_num_rows($query);
$query=mysql_query("SELECT vote FROM vote WHERE uservote='".$_SESSION['nickname']."'",$mydb);
echo mysql_num_rows($query);
$query = mysql_query("SELECT datereg FROM users WHERE nickname='".$_SESSION['nickname']."'",$mydb);
echo mysql_result($query,0,'datereg');
But this will call the MySql server 4 times.
Whats your suggestion to better this situation?
If the tables are not related then you will have to make 4 seperate calls
If the tables COULD be related by foreign keys then you could join them in some way and possibly cut down your sql calls
Ultimately though if you need all of the data then you'll have to request it from the database
You could use a UNION. And, btw, mysql_result is poor. And FFS don't forget to sanitize your inputs!
<?php
$nickname = mysql_escape_string($_SESSION['nickname']);
$sql = "
SELECT COUNT(trackid) AS n FROM tracklist WHERE usersub='{$nickname}'
UNION
SELECT COUNT(trackid) FROM comments WHERE usercom='{$nickname}'
UNION
SELECT COUNT(vote) FROM vote WHERE uservote='{$nickname}'
UNION
SELECT datereg FROM users WHERE nickname='{$nickname}'
";
$result = mysql_query($sql, $db);
while ($row = mysql_fetch_assoc($result)) {
echo $row['n'];
}
?>
I wouldn't really recommend this as it's a bit of a mess combining "count" values with a date in the same column, but you can do it. It's the direct answer to your question.
Well, you could create a fifth table and use it as an index.
If all the values { trackid, vote, datareg } are integers, the index table could contain three columns - nickname, value, and table. When you add records to one of the other tables, add a corresponding record to the index table.
For example,
INSERT INTO vote (vote, uservote, ...) VALUES (123, 'abc', ...);
INSERT INTO myindex (nickname, nvalue, ntable) VALUES ('abc', 123, 'vote');
(I wouldn't actually store the table name as a string but as a numeric value, but you get the idea)
Then on a query, you just SELECT nvalue, ntable FROM myindex WHERE nickname = 'abc';
You will possibly get more than one row.
I think that this is a lot of work and you are better off sticking with the four original queries.
Have you tried combining the select statement together like
SELECT .. Actually.
Maybe you should normalise your database and set up links between your tables...
Edit :: And i'm not sure how you're preparing yourself against mysql injection, but be careful with where your $_SESSION[] comes from
If all the selects return a single row:
$query=mysql_query("
(SELECT trackid FROM tracklist WHERE usersub='".$_SESSION['nickname']."'") as tracklist,
(SELECT trackid FROM comments WHERE usercom='".$_SESSION['nickname']."'") as trackid,
(SELECT vote FROM vote WHERE uservote='".$_SESSION['nickname']."'") as vote,
(SELECT datereg FROM users WHERE nickname='".$_SESSION['nickname']."'") as datereg
"
Related
I need to filter duplicates, but union is displaying duplicates.
For example Query-1 is displaying 5 tuples like 1,2,3,4,5.
Query-2 generating 3 tuples like 1,2,6.
Union of both the tuples displaying result 1,2,3,4,5,1,2,6.
But I want the result as 1,2,3,4,5,6.
Here is my controller :
public function product()
{
$product = $this->input->post('keyword');
$temp = explode(" ", $product);
$count = count($temp);
for($i=0;$i<$count;$i++)
{
$query = "SELECT * FROM `product` WHERE SOUNDEX(`name`) LIKE CONCAT('%',SOUNDEX('$temp[$i]'),'%') UNION SELECT * FROM `product` WHERE `name` like '%$temp[$i]%'";
$data = $this->Back_model->getby_query($query);
$records = json_encode($data);
echo $records;
}
}
There is no apparent reason for using 2 select queries, the second filter may be added to an existing where clause
SELECT *
FROM `product`
WHERE SOUNDEX(`name`) LIKE CONCAT('%',SOUNDEX('$temp[$i]'),'%')
AND `name` like '%$temp[$i]%'";
First of all, I would probably do this in another scripting language, but if you really want to do this in MySQL, you need to use DISTINCT. You should query the data and put it in a temp table, and from the temp table query the DISTINCT values. Once you're done you can drop the temp table. For an operation this small, not sure if this is what I would do, but if you say that you have thousands of records/values that need to be filtered, than it might be worth it.
Is there a better way to check if there are at least two rows in a table for a given condition?
Please look at this PHP code:
$result = mysql_query("SELECT COUNT(*) FROM table WHERE .......");
$has_2_rows = (mysql_result($result, 0) >= 2);
The reason I dislike this, is because I assume MySQL will get and count ALL the matching rows, which can be slow for large results.
I would like to know if there is a way that MySQL will stop and return "1" or true when two rows are found. Would a LIMIT 2 at the end help?
Thank you.
This is a good question, and yes there is a way to make this very efficient even for large tables.
Use this query:
SELECT count(*) FROM (
SELECT 1
FROM table
WHERE .......
LIMIT 2
) x
All the work is done by the inner query, which stops when it gets 2 rows. Also note the select 1, which gives you a tiny bit more efficiency, since it doesn't have to retrieve any values from columns - just the constant 1.
The outer count(*) will count at most 2 rows.
Note: Since this is an SQL question, I've omitted PHP code from the answer.
The query below will only inspect two rows as you request. mysql_num_rows can check how many rows are returned without any looping.
$result = mysql_query("SELECT col1 FROM t1 WHERE ... LIMIT 2");
if (mysql_num_rows($result) == 2) {
Please avoid using ext/mysql and switch to PDO or mysqli if you can.
$result = mysql_query("SELECT COUNT(*) FROM table WHERE .......");
if(mysql_num_rows($result) > 1)
{
echo 'at least 2 rows';
}
else
{
echo 'less than 2 rows';
}
Good evening guys,
I'm a newbie to web programming and I need your help to solve a problem inherent to SQL query.
The database engine I'm using is MySQL and I access it via PHP, here I'll explain a simplified version of my database, just to fix ideas.
Let's suppose to work with a database containing three tables: teams, teams_information, attributes. More precisely:
1) teams is a table containing some basic information about italian football teams (soccer, not american football :D), it is formed by three fields: 'id' (int, primary key), 'name' (varchar, team name), nickname (Varchar, team nickname);
2) attributes is a table containing a list of possible information about a football team, such as city (the city where team plays its home match), captain (team captain's fullname), f_number (number of fans) and so on. This table is formed by three fields: id (int, primary key), attribute_name (varchar, an identifier for the attribute), attribute_desc (text, an explanation of the meaning of attribute). Each record of this table represents a single possible attribute of a football team;
3) teams_information is a table where some information, about teams listed in team table, are available. This table contains three fields: id (int, primary key), team_id (int, a foreign key which identifies a team), attribute_id (int, a foreign key which identifies one of the attributes listed in attributes table), attribute_value (varchar, the value of the attribute). Each record represents a single attribute of a single team. In general, different teams will have a different number of information, so for some teams a large number of attributes will be available while for other teams only a small number of attributes will be available.
Note that relation between teams and teams_information is one to many and the same relation exists between attributes and teams_information
Well, given this model my purpose is to realize a grid (maybe with ExtJS 4.1) to show user the list of italian football team, each record of this grid will represent a single football team and will contain all possible attributes: some fields may be empty (because, for considered team, the correspondent attribute is unknown), while the others will contain the values stored in teams_information table (for the considered team).
According to the above grid's field are: id, team_name and a number of fields to represent all the different attributes listed in 'attributes' table.
My question is: can I realize such a grid by using a SINGLE SQL query (maybe a proper SELECT query, to fetch all data I need from database tables) ?
Can anyone suggest me how to write a similar query (if it exists) ?
Thanks in advance for helping me.
Regards.
Enrico.
The short answer to your question is no, there is no simple construct in MySQL to achieve the result set you are looking for.
But it is possible to carefully (painstakingly) craft such a query. Here is an example, I trust you will be able to decipher it. Basically, I'm using correlated subqueries in the select list, for each attribute I want returned.
SELECT t.id
, t.name
, t.nickname
, ( SELECT v1.attribute_value
FROM team_information v1
JOIN attributes a1
ON a1.id = v1.attribute_id AND a1.attribute_name = 'city'
WHERE v1.team_id = t.id ORDER BY 1 LIMIT 1
) AS city
, ( SELECT v2.attribute_value
FROM team_information v2 JOIN attributes a2
ON a2.id = v2.attribute_id AND a2.attribute_name = 'captain'
WHERE v2.team_id = t.id ORDER BY 1 LIMIT 1
) AS captain
, ( SELECT v3.attribute_value
FROM team_information v3 JOIN attributes a3
ON a3.id = v3.attribute_id AND a3.attribute_name = 'f_number'
WHERE v3.team_id = t.id ORDER BY 1 LIMIT 1
) AS f_number
FROM teams t
ORDER BY t.id
For 'multi-valued' attributes, you'd have to pull each instance of the attribute separately. (Use the LIMIT to specify whether you are retrieving the first one, the second one, etc.)
, ( SELECT v4.attribute_value
FROM team_information v4 JOIN attributes a4
ON a4.id = v4.attribute_id AND a4.attribute_name = 'nickname'
WHERE v4.team_id = t.id ORDER BY 1 LIMIT 0,1
) AS nickname_1st
, ( SELECT v5.attribute_value
FROM team_information v5 JOIN attributes a5
ON a5.id = v5.attribute_id AND a5.attribute_name = 'nickname'
WHERE v5.team_id = t.id ORDER BY 1 LIMIT 1,1
) AS nickname_2nd
, ( SELECT v6.attribute_value
FROM team_information v6 JOIN attributes a6
ON a6.id = v6.attribute_id AND a6.attribute_name = 'nickname'
WHERE v6.team_id = t.id ORDER BY 1 LIMIT 2,1
) AS nickname_3rd
I use nickname as an example here, because American soccer clubs frequently have more than one nickname, e.g. Chicago Fire Soccer Club has nicknames: 'The Fire', 'La Máquina Roja', 'Men in Red', 'CF97', et al.)
NOT AN ANSWER TO YOUR QUESTION, BUT ...
Have I mentioned numerous times before, how much I dislike working with EAV database implementations? What should IMO be a very simple query turns into an overly complicated beast of a potentially light dimming query.
Wouldn't it be much simpler to create a table where each "attribute" is a separate column? Then queries to return reasonable result sets would look more reasonable...
SELECT id, name, nickname, city, captain, f_number, ... FROM team
But what really makes me shudder is the prospect that some developer is going to decide that the LDQ should be "hidden" in the database as a view, to enable the "simpler" query.
If you go this route, PLEASE PLEASE PLEASE resist any urge you may have to store this query in the database as a view.
I'm going to take a slightly different route. Spencer's answer is fantastic, and it addresses the issue quite well, but there's still a large underlying problem.
The data that you are trying to display on the site is over-normalized in the database. I won't elaborate, since, again, Spencer's answer highlights the issue pretty well.
Rather, I'd like to recommend a solution that denormalizes the data a bit.
Convert all of your Team data into a single table with many columns. (If there is Player data that isn't covered in the question, that would be a second table, but I'll gloss over that for now.)
Sure, you'll have a whole bunch of columns, and a lot of the columns might be NULL for a lot of the rows. It's not normalized, and it's not pretty, but here's the huge advantage that you gain.
Your query becomes:
SELECT * FROM Teams
That's it. That gets displayed right to the website and you are done. You might have to go out of your way to realize this schema, but it would be totally worth the time investment.
I think what you're saying is that you want the rows in the attributes table to appear as columns in the result recordset. If this is correct, then then in SQL you would use PIVOT.
A quick search on SO seems to indicate that there is no PIVOT equivalent in MySql.
I wrote a simple PHP script to generalize spencer's idea to solve my issue.
Here's the code:
<?php
require_once('includes/db.config.php'); //this file performs connection to mysql
/*
* Following function requires a table name ($table)
* and a number of service fields ($num). Given those parameters
* it returns the number of table fields (excluding service fields).
*/
function get_fields_number($table,$num,$conn)
{
$query = "SELECT * FROM $table";
$result = mysql_query($query,$conn);
return mysql_num_fields($result)-$num; //remember there are $num service fields
}
/*
* Following function requires a table name ($table) and an array
* containing a list of service fields names. Given those parameters,
* it returns the list of field names. That list is contained within an array and
* service fields are excluded.
*/
function get_fields_name($table,$service,$conn)
{
$query = "SELECT * FROM $table";
$result = mysql_query($query,$conn);
$name = array(); //Array to be returned
for ($i=0;$i<mysql_num_fields($result);$i++)
{
if(!in_array(mysql_field_name($result,$i),$service))
{
//currently selected field is not a service field
$name[] = mysql_field_name($result,$i);
}
}
return $name;
}
//Below $conn is db connection created in 'db.config.php'
$query = "SELECT `name` FROM `detail_arg` WHERE visibility = 0";
$res = mysql_query($query,$conn);
if($res===false)
{
$err_msg = mysql_real_escape_string(mysql_error($conn));
echo "{success:false,data:'".$err_msg."'}";
die();
}
$arg = array(); //list of argument names
while($row = mysql_fetch_assoc($res))
{
$arg[] = $row['name'];
}
//Following function writes the select subquery which is
//necessary to build a column containing a single attribute.
function make_subquery($attribute) //$attribute contains attribute name
{
$query = "";
$query.="(SELECT incident_detail.arg_value ";
$query.="FROM incident_detail ";
$query.="INNER JOIN detail_arg ";
$query.="ON incident_detail.arg_id = detail_arg.id AND detail_arg.name='".$attribute."' ";
$query.="WHERE incident.id = incident_detail.incident_id) ";
$query.="AS $attribute";
return $query;
}
/*
echo make_subquery("date"); //debug code
*/
$subquery = array(); //list of subqueries
for($i=0;$i<count($arg);$i++)
{
$subquery[] = make_subquery($arg[$i]);
}
$query = "SELECT "; //final query containing subqueries
$fields = get_fields_name("incident",array("id","visibility"),$conn);
//list of 'incident' table's fields
for($i=0;$i<count($fields);$i++)
{
$query.="incident.".$fields[$i].", ";
}
//insert the subqueries
$sub = implode($subquery,", ");
$query .= $sub;
$query.=" FROM incident ORDER BY incident.id";
echo $query;
?>
I have two tables: Users and Groups
In my table "Users", there is a column called "ID" for all the user ids.
In my table "Groups" there is a column called "Participants", fields in this column are filled with all the user ids like this "PID_134,PID_489,PID_4784," - And there is a column "ID" that identifies a specific group.
Now what i want to do, i want to create a menu that shows all the users that are not yet in this particular group.
So i need to get all the user ids, that are not yet in the Participants column of a group with a particular ID.
It would be cool if there was a single mysql query for that - But any PHP + MySQL solutions are okay, too.
How does that work? Any guesses?
UPDATE:
i know, that's not code, but is there a way I could do something like this that would return me a list of all the users?
SELECT *
FROM users, groups
WHERE groups.participants NOT LIKE '%PID_'users.id'%' AND groups.id = 1;
Something like this. You just get rid of "PID_" part of ID.
SELECT * FROM [users] WHERE [id] NOT IN
(SELECT replace(id,'PID_','') FROM groups WHERE group_name='group1')
Group1 would be your variable - group id/name of menu that you've opened.
You can select from multiple tables as shown below:
SELECT * from users, groups WHERE users.id != groups.participants AND groups.id = 1;
This will list all users who are not in group id 1; A more elegant solution can be found by using joins, but this is simple and will do the trick.
I believe something like that should help:
SELECT * FROM users WHERE users.id NOT IN (SELECT groups.participants FROM groups)
But this works only if your DB is normalized. So for your case I see only PHP + MySQL solution. Not very elegant, but it does the job.
<?php
$participants_array = mysql_query("SELECT participants FROM groups");
$ids = array();
while ($participant = mysql_fetch_assoc($participants_array))
{
$id = explode(',', $participant['participant']);
foreach ($id as $instance)
{
if (!in_array($instance, $ids)) $ids[] = $instance;
}
}
$participants = implode(',', $ids);
$result = mysql_query("SELECT * FROM users WHERE id NOT IN ( $participants )");
But I highly recommend normalizing the database.
this is my database
database schema http://slashdir.com/php/blogg/images/bloggdb.png
What i want to do, is, for a given userid, show the total times he has been reported.
I have read various other questions on the matter, but I'm still stumped.
The latest query i tried was
select
sum(posts.timesreported + comments.timesreported) AS total_reports
FROM
posts
INNER JOIN comments ON (posts.userid = comments.userid)
WHERE posts.userid=5 AND comments.userid=5;
But this must be wrong as the number i get is much too high
Thanks!
SELECT
CASE WHEN NULL
THEN 0
ELSE (select sum(posts.timesreported) AS total_posts_reports
FROM posts INNER JOIN users ON (posts.userid = users.id)
WHERE posts.userid=5)
END
+
CASE WHEN NULL
THEN 0
ELSE (select sum(comments.timesreported) AS total_comments_reports
FROM comments INNER JOIN users ON (comments.userid = users.id)
WHERE comments.userid=5)
END
FROM DUAL;
Instead of
sum(posts.timesreported + comments.timesreported) AS total_reports
try
sum(posts.timesreported) + sum(comments.timesreported) AS total_reports
and I think you need to group by userId
WHERE posts.userid=5 AND comments.userid=5; is unnecessary since the tables are joined.
And sum operator is not correct logically
Use this query
select
sum(posts.timesreported) + sum(comments.timesreported) AS total_reports
FROM
posts
INNER JOIN comments ON (posts.userid = comments.userid)
WHERE posts.userid=5
It looks like your collecting the sum PRIOR to singling out the user. Perhaps this is adding those column values for all users prior to the join? What happens if you SELECT *, perform your INNER JOIN where userid = 5. Save the column values as two variables and then try to add them. Do you get the same result?
This might help you error check to see if the above theory is accurate.
<?php
// Connects to your Database
mysql_connect("your.hostaddress.com", "username", "password") or die(mysql_error());
mysql_select_db("Database_Name") or die(mysql_error());
//Run Query
$NUM1=mysql_query("SELECT Field1 FROM Table WHERE user.key=5");
$NUM2=mysql_query("SELECT Field2 FROM Table WHERE user.key=5");
//Print Each Result
echo 'Num1 = '.$NUM1;
echo 'Num2 = '.$NUM2;
//Print Total
$TOTAL = $NUM1 + $NUM2;
echo 'Total = '.$TOTAL;
?>