Part of my page I have lots of small little queries, probably about 6 altogether, grabbing data from different tables. As an example:
$sql_result = mysql_query("SELECT * FROM votes WHERE voted_on='$p_id' AND vote=1", $db);
$votes_up = mysql_num_rows($sql_result);
$sql_result = mysql_query("SELECT * FROM votes WHERE voted_on='$p_id' AND vote=0", $db);
$votes_down = mysql_num_rows($sql_result);
$sql_result = mysql_query("SELECT * FROM kids WHERE (mother_id='$p_id' OR father_id='$p_id')", $db);
$kids = mysql_num_rows($sql_result);
Would it be better if these were all grabbed in one query to save trips to the database? One query is better than 6 isn't it?
Would it be some kind of JOIN or UNION?
Its not about number of queries but amount of useful datas you transfer. If you are running database on localhost, is better to let sql engine to solve queries instead computing results in additional programs. The same if you are thinking about who should be more bussy. Apache or mysql :)
Of course you can use some conditions:
SELECT catName,
SUM(IF(titles.langID=1, 1, 0)) AS english,
SUM(IF(titles.langID=2, 1, 0)) AS deutsch,
SUM(IF(titles.langID=3, 1, 0)) AS svensk,
SUM(IF(titles.langID=4, 1, 0)) AS norsk,
COUNT(*)
FROM titles, categories, languages
WHERE titles.catID = categories.catID
AND titles.langID = languages.
example used from MYSQL Bible :)
If you really want to lower the number of queries, you can put the first two together like this:
$sql_result = mysql_query("SELECT * FROM votes WHERE voted_on='$p_id'", $db);
while ($row = mysql_fetch_array($sql_result))
{
extract($row);
if ($vote=='0') ++$votes_up; else ++$votes_down;
}
The idea of joining tables is that these tables are expected to have something in between (a relation, for example).
Same is for the UNION SELECTS, which are prefered to be avoided.
If you want your solution to be clean and scalable in future, I suggest you to use mysqli, instead of mysql module of PHP.
Refer to: mysqli::multi_query. There is OOP variant, where you create mysqli object and call the function as method.
Then, your query should look like:
// I use ; as the default separator of queries, but it might be different in your case.
// The above could be set with sql statement: DELIMITER ;
$query = "
SELECT * FROM votes WHERE voted_on='$p_id' AND vote=1;
SELECT * FROM votes WHERE voted_on='$p_id' AND vote=0;
SELECT * FROM kids WHERE (mother_id='$p_id' OR father_id='$p_id');
";
$results = mysqli_multi_query($db, $query); // Returns an array of results
Fewer queries are (generally, not always) better, but it's also about keeping your code clear enough that others can understand the query. For example, in the code you provided, keep the first two together, and leave the last one separate.
$sql_result = mysql_query("SELECT vote, COUNT(*) AS vote_count
FROM votes
WHERE voted_on='$p_id'
GROUP BY vote", $db);
The above will return to you two rows, each containing the vote value (0 or 1) and the vote count for the value.
Related
I have the following two queries. The first query is fetching a key called srNumber from first table called tags and then the second query is using that srNumber to fetch details from a second table called nexttable.
$tagQuery = "SELECT * FROM tags WHERE status = 0 AND currentStage = '1' AND assignedTo = '1' ORDER BY
deliveryDate ASC";
$tagQueryExecute = mysqli_query($conn, $tagQuery);
while($rows = mysqli_fetch_array($tagQueryExecute)){
$srNumber = $rows['srNumber'];
$nextQuery = "SELECT * FROM nexttable WHERE srNumber='$srNumber'";
$nextQueryExecute = mysqli_query($conn, $nextQuery);
$detailsFromNextTable = mysqli_fetch_array($nextQueryExecute);
//Show these details
}
For a small result this is not a big issue. But if the first query got so many results, then second query has to run as many times as number of loop. Is there any other way to do this efficiently?
NB: Please ignore the SQL injection issues with these queries. I just simplified it to show the problem
As you appear to have only 1 row in the second table, you would be better off with a join, MySQL: Quick breakdown of the types of joins gives some more info on the types of joins.
SELECT *
FROM tags t
JOIN nexttable n on t.srNumber = n.srNumber
WHERE t.status = 0 AND t.currentStage = '1' AND t.assignedTo = '1'
ORDER BY t.deliveryDate ASC
This also removes the SQL injection as well.
I would also recommend removing the * and just list the columns you intend to use, this also helps if you have columns with the same names in the different tables as you can add an alias to the specific columns.
FYI - the original problem you have is similar to What is the "N+1 selects problem" in ORM (Object-Relational Mapping)?
my foundation on SQL is pretty weak so I hope you could bear with me. I have three tables: contents, categories, and categorization. The setup was chosen since some content will belong to one or more categories.
I want to fetch contents and its corresponding categories.
This is an overly-simplified version of the current script, without error-checking routines:
$q = "SELECT * FROM contents WHERE contents.foo = 'bar'"
$resource = mysql_query($q);
$categoryFilter = array();
$q2 = "SELECT * FROM categorization WHERE ";
while($content = mysql_fetch_assoc($resource))
{
$categoryFilter[] = "content_id='" . $content["id"] . "'";
}
if(count($categoryFilter))
{
$q2 .= implode(" OR ", $categoryFilter);
mysql_query($q2);
}
That's the gist of it. I hope you get what I am trying to do. I don't know if I can actually use JOINS the content_id may be present in multiple rows in categorization. So what I did was to simply append multiple OR's, trying to fetch items one by one. I really would not like to use multiple queries in this scenario. I hope anyone could suggest an approach
Thanks for your time
One query should be enough to fetch data from all three tables:
SELECT categories.category_id #, other fields
FROM contents
INNER JOIN categorization ON contents.content_id = categorization.content_id
INNER JOIN categories ON categorization.category_id = categories.category_id
WHERE contents.content_id = 1 # AND other filters
Tweak the columns in the SELECT clause and/or conditions in WHERE clause according to your needs.
This should do the same thing as in your example:
$q = "
SELECT *
FROM
contents c
categorization ctg ON ctg.content_id = c.id
WHERE c.foo = 'bar'
";
$result = mysql_query($q);
If I understand it correctly, you can do this in one sql statement
SELECT *
FROM contents t1
JOIN categorization t2
WHERE t1.content_id = t2.content_id AND t1.foo = 'bar'
Also ensure that content_id is indexed both in 'content' and 'categorization'. You may find it worthwhile indexing 'foo' aswell, but it depends on how you are actually searching.
I have the following 3 tables in the database.
Programs_Table
Program_ID (Primary Key)
Start_Date
End_Date
IsCompleted
IsGoalsMet
Program_type_ID
Programs_Type_Table(different types of programs, supports a dropdown list in the form)
Program_type_ID (Primary Key)
Program_name
Program_description
Client_Program_Table
Client_ID (primary key)
Program_ID (primary key)
What is the best way to find out how many clients are in a specific program (program type)?
Would the following SQL statement be the best way, or even plausible?
SELECT Client_ID FROM Client_Program_Table
INNER JOIN Programs_Table
ON Client_Program_Table.Program_ID = Programs_Table.Program_ID
WHERE Programs_Table.Program_type_ID = "x"
where "x" is the Program_type_ID of the specific program we're interested in.
OR is the following a better way?
$result = mysql_query("SELECT Program_ID FROM Programs_Table
WHERE Program_type_ID = 'x'");
$row = mysql_fetch_assoc($result);
$ProgramID = $row['Program_ID'];
$result = mysql_query("SELECT * FROM Client_Program_Table
WHERE Program_ID = '$ProgramID'");
mysql_num_rows($result) // returns how many rows of clients we pulled.
Thank you in advance, please excuse my inexperience and any mistakes that I've made.
Here is how you can do it:
<?php
// always initialize a variable
$number_of_clients = 0;
// escape the string which will go in an SQL query
// to protect yourself from SQL injection
$program_type_id = mysql_real_escape_string('x');
// build a query, which will count how many clients
// belong to that program and put the value on the temporary colum "num_clients"
$query = "SELECT COUNT(*) `num_clients` FROM `Client_Program_Table` `cpt`
INNER JOIN `Programs_Table` `pt`
ON `cpt`.`Program_ID` = `pt`.`Program_ID`
AND `pt`.`Program_type_ID` = '$program_type_id'";
// execute the query
$result = mysql_query($query);
// check if the query executed correctly
// and returned at least a record
if(is_resource($result) && mysql_num_rows($result) > 0){
// turn the query result into an associative array
$row = mysql_fetch_assoc($result);
// get the value of the "num_clients" temporary created column
// and typecast it to an intiger so you can always be safe to use it later on
$number_of_clients = (int) $row['num_clients'];
} else{
// query did not return a record, so we have no clients on that program
$number_of_clients = 0;
}
?>
If you want to know how many clients are involved in a program, you'd rather want to use COUNT( * ). MySQL (with MyISAM) and SQL Server have a fast way to retrieve the total number of lines. Using a SELECT(*), then mysql_num_rows leads to unnecessary memory ressources and computing time. To me, this is the fastest, though not the "cleanest" way to write the query you want:
SELECT
COUNT(*)
FROM
Client_Program_Table
WHERE
Program_ID IN
(
SELECT
Program_ID
FROM
Programs_Table
WHERE
Program_type_ID = 'azerty'
)
Why is that?
Using JOIN make queries more readable, but subqueries often prove to be computed faster.
This returns a count of the clients in a specific program type (x):
SELECT COUNT(cpt.Client_ID), cpt.Program_ID
FROM Client_Program_Table cpt
INNER JOIN Programs_Table pt ON cpt.Program_ID=pt.Program_ID
WHERE pt.Program_type_ID = "x"
GROUP BY cpt.Program_ID
// make empty array
$sqlArray=array();
$jsonArray=array();
// START NEED FAST WORKING ALTERNATİVES -----------------------------------------------------
// first 20 vistors
$query = "SELECT user_id FROM vistors LIMIT 20";
$result = mysql_query ($query) or die ($query);
// make vistors user query array
while ($vstr_line = mysql_fetch_array($result)){
array_push($sqlArray, $vstr_line['user_id']);
}
// implode vistors user array
$sqlArray_impl = implode("', '", $sqlArray);
// END NEED FAST WORKING ALTERNATİVES -----------------------------------------------------
// Get vistors information
$query = "SELECT id, username, picture FROM users WHERE id IN ('$sqlArray_impl')";
$qry_result = mysql_query($query) or die($query);
while ($usr_line = mysql_fetch_array($qry_result)){
array_push($jsonArray, $usr_line['id'].' - '.$usr_line['username'].' - '.$usr_line['picture']);
}
print_r($sqlArray);
echo '<br><br>';
print_r($jsonArray);
see this my functions..
i need a replacement for fast working alternatives..
function within the range specified above, to me, running faster than the alternative.
the query will return back array ?
thx for all helpers !
Can you use a JOIN or SUB SELECT to reduce the query count from 2 to 1? Might not give much of a boost but worth a shot and a cleaner implementation.
Where is the bottleneck? Most likely the db and not the php code.
Are the tables/columns properly indexed? Run EXPLAIN on both queries.
Easiest would be to include first query as subquery eliminating one turn to the DB and a lot of code:
// Get vistors information
$query = "SELECT id, username, picture FROM users WHERE id IN (SELECT user_id FROM vistors LIMIT 20)";
$qry_result = mysql_query($query) or die($query);
Unless there is more reason to have the first one seperate, but that is not visible in your code example.
If you use PDO (recommended anyway...), you can return the result array all at once using fetchAll().
For your second query, you can use string concatenation in MySQL to directly return the result you want.
I'm doing this project for university, which is basically a movie database and for a couple of queries I need to know how many rows were selected. For now, there's 2 situations where I need this:
Display a single movie information. I want the count of selected rows to know if the database contains the selected movie by the user. Or is there a better solution for this?
That selected movie has genres, I need to know how many so that I can construct a string with the genres separated by | without adding one to the end of the string.
With MySQL this is easy, I just query the database and use mysql_num_rows() but oci_num_rows() doesn't work quite the same for the SELECT statement.
The only solution I found with OCI/PHP is this:
if(is_numeric($mid) && $mid > 0) {
$stid = oci_parse($db,
'SELECT COUNT(*) AS NUM_ROWS
FROM movies
WHERE mid = '.$mid
);
oci_define_by_name($stid, 'NUM_ROWS', $num_rows);
oci_execute($stid);
oci_fetch($stid);
if($num_rows > 0) {
$stid = oci_parse($db,
'SELECT title, year, synopsis, poster_url
FROM movies
WHERE mid = '.$mid
);
oci_execute($stid);
$info = oci_fetch_assoc($stid);
$stid = oci_parse($db,
'SELECT COUNT(*) AS NUM_ROWS
FROM genres g, movies_genres mg
WHERE mg.mid = '.$mid.' AND g.gid = mg.gid'
);
oci_define_by_name($stid, 'NUM_ROWS', $num_rows);
oci_execute($stid);
oci_fetch($stid);
$stid = oci_parse($db,
'SELECT g.name AS genre
FROM genres g, movies_genres mg
WHERE mg.mid = '.$mid.' AND g.gid = mg.gid');
oci_execute($stid);
$genres_list = null;
while($row = oci_fetch_assoc($stid)) {
$genres_list .= $row['GENRE'];
if($num_rows > 1) {
$genres_list .= ' | ';
$num_rows--;
}
}
$Template->assignReferences(array(
'Index:LinkURI' => $link_uri,
'Movie:Title' => $info['TITLE'],
'Movie:Year' => $info['YEAR'],
'Movie:GenresList' => $genres_list,
'Movie:Synopsis' => $info['SYNOPSIS'],
'Movie:PosterURL' => $info['POSTER_URL'] // FIX: Handle empty poster link
));
$Template->renderTemplate('movieinfo');
} else {
// TODO: How to handle this error?
}
} else {
// TODO: How to handle this error?
}
But I don't like it. I always need to make 2 queries to count the rows and then select the actual data and there's too many lines of code just to count the rows.
This code doesn't show it (haven't done it yet cause I'm looking for a better solution) but I'll also need to do the same for the movie directors/writers.
Is there any better and simpler solution to accomplish this or this is the only way?
I could add separators in the fetch loop until it finishes and then use PHP functions to trim the last separator from the string, but for this project I'm forced to use SEQUENCES, VIEWS, FUNCTIONS, PROCEDURES and TRIGGERS. Do any of these help solving my problem?
I know what SEQUENCES are, I'm using them already but I don't see how can they help.
For VIEWS, they probably wouldn't simplify the code that much (it's basically a stored query right?). For FUNCTIONS, PROCEDURES and TRIGGERS, as far as I understand them, I can't see how can they be of any help either.
Solutions?
Why do the initial count at all? Just issue your select for the movie title. If it's not found, do your error processing. If it is, continue on! If you really need the count, use an analytic to add the count to your query:
'SELECT title, year, synopsis, poster_url
, COUNT(*) OVER (PARTITION BY mid) mcount
FROM movies
WHERE mid = '.$mid
The same goes for your genre selection.
EDIT:
Oracle documentation on Analytic Functions link. I found that analytics are a bit difficult to get from the Oracle docs. Analytic functions by Example by Shouvik Basu provides some simple guidance as to how to use them and helped me quite a bit.
You can try this
$conn = oci_pconnect('user', 'password', 'connectionstring');
$resource = oci_parse($conn, $sql);
oci_execute($resource, OCI_DEFAULT);
$results=array();
$numrows = oci_fetch_all($resource, $results, null, null, OCI_FETCHSTATEMENT_BY_ROW);
Cheers
you can use the ocirowcount it should behave just like mysql_num_rows when making a select
oci_num_rows() Will give you the total row count if executed AFTER oci_fetch_array()