I have page that display information from two different tables , and for that I have two queries.
There is no related info between these two tables.
Since both queries may contain a lot of information, I need create pagination.
BUT I don't want two separate paginations, I want only one that will contain results from query 1 and query 2 together.
How can I do that?
The only idea I have is to fetch all info of both queries into arrays, then combine the arrays into one, then create pagination that based on that array.
That of course would not help save resources.
You could use a union - the columns you're displaying must line up, so something like this should work:
select
col1 col1_alias,
col2 col2_alias,
...
from
table1
where
...
union
select
col1,
col2,
...
from
table2
where
...
order by col1_alias, col2_alias
limit 10
Basically the union will pull all the data together, and the order by and limit will apply to the whole result set.
The names of the columns don't need to match in the second select, but use column names from the first select for your order by (or create aliases, which is probably more readable depending on your dataset).
Related
Here is the problem: I want my data sorted in 2 differents way without calling two times the database.
Example:
SELECT data FROM costumers WHERE x ORDER BY budget, car, home
I need this data sorted in this way to do fast some operations.
In the meantime I need also the same data but:
ORDER BY home, budget, car
I can reorder the data in php or make a second query to my database but I hope there is a simplee and faster way to make it works with MySql.
(maybe the data could be fetch in two differents ways)
Thanks in advance :)
(first time I post, but not first time this website helps me)
you can do this sort in one query .
example if we have col1 and col2. col1 contain strings and col2 contains numbers
SELECT * FROM table
ORDER BY `col1` DESC, `col2` DESC
we assume cols values are
(col1, col2): (b,3), (a,4), (c,1), (a,1)
after we execute the query above it will return the records in this order
(col1, col2): (a,1), (a,4), (b,3), (c,1)
note: MySQL uses the first arg of order by as more impotent than second and so on. Even you can sort by triple or more in this way and even the date type could be ordered too.
i have multiple table that join together and i need one query and get all references too ! is that possible in yii2??
get them in hierarchy array ??
How ???
Is it possible to do not use join???
thanks for your help!!!!
If you created the model classes for each table using Gii and selected to create the relations in the generated models, you can do something like the following.
1) In your Countries model just change the method that declares the relationship with Airports like this:
public function getAirports() {
return $this->hasMany(Airports::className(), ['country_id' => 'id'])->with('airlines');
}
2) When you do the query for the countries and you need to have the related airports, airlines and flightbooked do it like this:
$countries = Countries::find()
->where('something = something_else')
->with('airports')
->with('flightbooked')
->all();
This way you will get all the related models populated with way less queries to the database than using lazy-loading.
I just wanted to give a small suggestion:
As you are maintaining the relations in the tables and if you have generated your code using Gii, then that will generate the joins for you. You can then access any column of any table easily.
But I think UNION may not be an alternative to JOIN.
Maybe u can use union all for this. with this operator, you can concatenate the result sets from multiple queries together, preserving all of the rows from each. Note that a UNION operator (without the ALL keyword) will eliminate any "duplicate" rows which exist in the resultset. The UNION ALL operator preserves all of the rows from each query (and will likely perform better since it doesn't have the overhead of performing the duplicate check and removal operation).
The number of columns and data type of each column must match in each of the queries. If one of the queries has more columns than the other, we sometimes include dummy expressions in the other query to make the columns and datatypes "match". Often, it's helpful to include an expression (an extra column) in the SELECT list of each query that returns a literal, to reveal which of the queries was the "source" of the row.
SELECT 'col1' AS source, col23, col343, col33, d FROM table1 WHERE ...
UNION ALL
SELECT 'col2', t2.fee, table2.fi, table2.fo, 'fum' FROM table2 JOIN table3 ON ...
UNION ALL
SELECT 'col3', '1', '2', buckle, my_shoe FROM table4
You can wrap a query like this in a set of parenthesis, and use it as an inline view (or "derived table", in MySQL lingo), so that you can perform aggregate operations on all of the rows. e.g:
select one.a
, SUM(one.b)
FROM (
SELECT 'q1' AS source, a, b, c, d FROM t1
UNION ALL
SELECT 'q2', t2.fee, t2.fi, t2.fo, 'fum' FROM t2
) one
GROUP BY one.a
ORDER BY one.a
But i think joining tables more suitable. Hope help you
I am currently working on a school system where we have a parent course and a child course (meta_courses in Moodle).
So, we have a table mdl_course_meta and it has 3 fields. Id, parent_course and child_course.
My problem is that a parent course can have many child courses so that means, for example, a parent_course = 50 can appear two times in the table which means it has 2 child courses. I just want to be able to find all the parent courses without it returning the same value twice or more times. I'm currently using this query right now which obviously doesn't do what I want:
$q = "SELECT * FROM mdl_course_meta";
I am working with PHP as well by the way.
Thanks a lot.
SELECT DISTINCT parent_course from mdl_course_meta
That should do it if you just want the course names. One thing to keep in mind, if you want other fields this is not going to work the way you want it to(how would it know which record to choose if there are multiple records with the same parent_course and you only want one).
This approach can only be used if you only want to return the parent_courses without duplicates.
DISTINCT helps to eliminate duplicates. If a query returns a result that contains duplicate rows, you can remove duplicates to produce a result set in which every row is unique. To do this, include the keyword DISTINCT after SELECT and before the output column list.
$q = "SELECT DISTINCT parent_course FROM mdl_course_meta";
If you don't want duplicate values in a single column, use GROUP BY parent_course.
In this way you are free to select any column.
If you only want distinct values for a particular column column, then you can use GROUP BY:
SELECT *
FROM mdl_course_meta
GROUP BY parent_course
The values in the other columns will be arbitrary. This will work in MySQL 5.x.
MySQL 4.x won't let you be arbitrary, so you can't mix aggregate and non-aggregate columns. Instead, you'd have to do something like this, which gets a bit complicated:
SELECT MAX(col1), MAX(col2), parent_course, MAX(col4), ...
FROM mdl_course_meta
GROUP BY parent_course
This way, the values aren't arbitrary. You've specified the ones you want.
I currently have a page that displays player information from one table named "tblplayers". The query I am currently using is:
$result = mysql_query("SELECT * FROM tblPlayers WHERE lng_RecordID_PK = '".$playerid."' ");
I have a second table named "tblMatches" containing match results for the players. I want the recordset to include the rows from "tblMatches" WHERE "P1_ID" OR "P2_ID" is equal to the "lng_RecordID_PK" field from "tblPlayers".
How can I revise my $result query so that it returns:
one row from tblPlayers
multiple rows from tblMatches
???
Thanks for helping me out.
That's called a 'join':
SELECT tblPlayers.*, tblMatches.*
FROM tblPlayers
LEFT JOIN tblMatches ON Ing_RecordID_PK IN (P1_ID, P2_ID)
You are asking about joining two tables where the second table potentially has multiple records for each one in the first table. This is a one-to-many or 1:N join, and most often done using a LEFT JOIN meaning you want everything in the "left" table, and all the records that match from the "right" table, and that you may have some records on the "left" side with no matches.
Your query would look like this:
SELECT *
FROM tblPlayers
LEFT JOIN tblMatches
ON (tblPlayers.lng_RecordID_PK = tblMatches.P1_ID
OR tblPlayers.lng_RecordID_PK = tblMatches.P2_ID)
WHERE tblPlayers.lng_RecordID_PK = #PlayerID;
Bits of advice:
Avoid selecting all columns (*) and instead select just those that you need for the query.
Consider using parameterized queries to avoid SQL injection attacks. If your variable were to be submitted or altered maliciously, it could result in compromised data or security. (See PHP Data Objects for example.)
There is no way to get rows from two different tables in the way you are describing. You could not get a row from one table, and two rows from another one. What you could is do two separate queries, or use a JOIN statement to join the two tables together, and then receive results from the resulting joined table. If you provide more information about your table structure I am sure more help can be given.
I'm trying to query 2 tables where the first table will return 1 row and the second table will return multiple rows. So basically the first table with return text on a page and the second table will return a list that will go within the page. Both tables have a reference row which is what both tables are queried on. (See Below)
SELECT shop_rigs.*, shop_rigs_images.*, shop_rigs_parts.*
FROM shop_rigs
LEFT JOIN shop_rigs_images
ON shop_rigs.shoprigs_ref = shop_rigs_images.shoprigsimg_ref
LEFT JOIN shop_rigs_parts
ON shop_rigs.shoprigs_ref = shop_rigs_parts.shoprigsparts_ref
WHERE shoprigs_enabled='1' AND shoprigs_ref='$rig_select'
ORDER BY shoprigs_order ASC
Is it better to just do 2 queries?
Thanks,
dane
I would do this in two queries. The problem isn't efficiency or the size of the respective tables, the problem is that you're create a Cartesian product between shop_rigs_images and shop_rigs_parts.
Meaning that if a given row of shop_rigs has three images and four parts, you'll get back 3x4 = 12 rows for that single shop_rig.
So here's how I'd write it:
SELECT ...
FROM shop_rigs
INNER JOIN shop_rigs_images
ON shop_rigs.shoprigs_ref = shop_rigs_images.shoprigsimg_ref
WHERE shoprigs_enabled='1' AND shoprigs_ref='$rig_select'
ORDER BY shoprigs_order ASC
SELECT ...
FROM shop_rigs
INNER JOIN shop_rigs_parts
ON shop_rigs.shoprigs_ref = shop_rigs_parts.shoprigsparts_ref
WHERE shoprigs_enabled='1' AND shoprigs_ref='$rig_select'
ORDER BY shoprigs_order ASC
I left the select-list of columns out, because I agree with #Doug Kress that you should select only the columns you need from a given query, not all columns with *.
If you're pulling a large amount of data from the first table, then it would be better to do two queries.
Also, for efficiency, it would be better to specify each column that you actually need, instead of all columns - that way, less data will be fetched and retrieved.
Joins are usually more efficient than running 2 queries, as long as you are joining on indexes, but then it depends on your data and indexes.
You may want to run a "explain SELECT ....." for both options and compare "possible keys" and "rows" from your results.