I have a MySQL database that I have to get information from, said information is spread across different tables and I have been Googling for a while for the best method to get this information and found quite some information, but I was wondering if there is a best practice that I should try, since the tables may get quite big later on I would like to have a good start regarding functionality, and speed.
If your records in your database are related through ID's or primary keys, you can use the JOIN syntax to get data from multiple tables through 1 query.
Example :
Table car : id, brand
Table driver : id, name, car_id
You can get all the drivers of a car in 1 query:
SELECT * FROM driver LEFT JOIN car ON (car.id = driver.car_id) WHERE car.id=5;
This is just a basic example, but read the MySql documentation (or tutorials) to go on.
Related
I'm working on an existing application that uses some JOIN statements to create "immutable" objects (i.e. the results are always JOINed to create a processable object - results from only one table will be meaningless).
For example:
SELECT r.*,u.user_username,u.user_pic FROM articles r INNER JOIN users u ON u.user_id=r.article_author WHERE ...
will yield a result of type, let's say, ArticleWithUser that is necessary to display an article with the author details (like a blog post).
Now, I need to make a table featured_items which contains the columnsitem_type (article, file, comment, etc.) and item_id (the article's, file's or comment's id), and query it to get a list of the featured items of some type.
Assuming tables other than articles contain whole objects that do not need JOINing with other tables, I can simply pull them with a dynamicially generated query like
SELECT some_table.* FROM featured_items RIGHT JOIN some_table ON some_table.id = featured_items.item_id WHERE featured_items.type = X
But what if I need to get a featured item from the aforementioned type ArticleWithUser? I cannot use the dynamically generated query because the syntax will not suit two JOINs.
So, my question is: is there a better practice to retrieve results that are always combined together? Maybe do the second JOIN on the application end?
Or do I have to write special code for each of those combined results types?
Thank you!
a view can be thot of as like a table for the faint of heart.
https://dev.mysql.com/doc/refman/5.0/en/create-view.html
views can incorporate joins. and other views. keep in mind that upon creation, they take a snapshot of the columns in existence at that time on underlying tables, so Alter Table stmts adding columns to those tables are not picked up in select *.
An old article which I consider required reading on the subject of MySQL Views:
By Peter Zaitsev
To answer your question as to whether they are widely used, they are a major part of the database developer's toolkit, and in some situations offer significant benefits, which have more to do with indexing than with the nature of views, per se.
I need to JOIN 2 tables (lets say User & Order table) for reporting module in my web app.
The problems are:
The User table is located on the different server & different
DBMS from the Order table. Technically it is a different system, so the User table is located on SQL Server DB, meanwhile the Order table is located on MySQL DB.
I couldn't use SQL Server's Linked Server because my company policy doesn't allow it. So, I coudn't JOIN them directly with SQL code. They want me to use Web Service instead of linked server.
The result of JOIN operation from those tables has a large number of rows (maybe more than 10,000 rows because the data aimed for reporting). So, I think it was a horrible thing to mapping them using Web Service.
So I came up with this:
I collected 2 query result from different models and join them with my app code (I'm using PHP with CodeIgniter) :
// First result
$userData = $this->userModel->getAllUser();
// Second result
$orderData = $this->orderModel->getAllOrder();
The $userData contains all user entities with the following columns:
[UserId, Username, Address, PhoneNumber, etc..]
And the $orderData contains all order entities with the following columns:
[OrderId, UserId, Date, etc..]
But is it possible to join those two query results in PHP / CodeIgniter?
How about the performance regarding the large amount of data?
Should I just use Web Service as suggested or there's another solution to accomplish this?
Thanks in advance :)
A few things to think about:
Do you actually need to return all user and order records in one single go
Do you actually want to return all rows for these two types of record
Would you be better off with a Report module for these report queries?
Would plain SQL syntax be a smarter move than trying to shim this into existence with the CodeIgniter "Active Record" (renamed Query Builder in 3.0)
Is JOIN really so bad? It is not a UNION, you want the data to be related.
I would recommend you limit your data returns, SELECT only the fields you actually require, make a new Report model to avoid trying to mess up your generic models and do this with raw SQL.
Complicated things get all the more complicated when you try too hard to stick to rules like "1 table = 1 model" and "User::getAllFoos + controller processing > Report::getMonthlyOrderStats()".
im kinda new with mysql and i'm trying to create a kind complex database and need some help.
My db structure
Tables(columns)
1.patients (Id,name,dob,etc....)
2.visits (Id,doctor,clinic,Patient_id,etc....)
3.prescription (Id,visit_id,drug_name,dose,tdi,etc....)
4.payments (id,doctor_id,clinic_id,patient_id,amount,etc...) etc..
I have about 9 tables, all of them the primary key is 'id' and its set to autoinc.
i dont use relations in my db (cuz i dont know if it would be better or not ! and i never got really deep into mysql , so i just use php to run query's to Fitch info from one table and use that to run another query to get more info/store etc..)
for example:
if i want to view all drugs i gave to one of my patients, for example his id is :100
1-click patient name (name link generated from (tbl:patients,column:id))
2-search tbl visits WHERE patient_id=='100' ; ---> that return all his visits ($x array)
3-loop prescription tbl searching for drugs with matching visit_id with $x (loop array).
4- return all rows found.
as my database expanding more and more (1k+ record in visit table) so 1 patient can have more than 40 visit that's 40 loop into prescription table to get all his previous prescription.
so i came up with small teak where i edited my db so that patient_id and visit_id is a column in nearly all tables so i can skip step 2 and 3 into one step (
search prescription tbl WHERE patient_id=100), but that left me with so many duplicates in my db,and i feel its kinda stupid way to do it !!
should i start considering using relational database ?
if so can some one explain a bit how this will ease my life ?
can i do this redesign but altering current tables or i must recreate all tables ?
thank you very much
Yes, you should exploit MySQL's relational database capabilities. They will make your life much easier as this project scales up.
Actually you're already using them well. You've discovered that patients can have zero or more visits, for example. What you need to do now is learn to use JOIN queries to MySQL.
Once you know how to use JOIN, you may want to declare some foreign keys and other database constraints. But your system will work OK without them.
You have already decided to denormalize your database by including both patient_id and visit_id in nearly all tables. Denormalization is the adding of data that's formally redundant to various tables. It's usually done for performance reasons. This may or may not be a wise decision as your system scales up. But I think you can trust your instinct about the need for the denormalization you have chosen. Read up on "database normalization" to get some background.
One little bit of advice: Don't use columns named simply "id". Name columns the same in every table. For example, use patients.patient_id, visits.patient_id, and so forth. This is because there are a bunch of automated software engineering tools that help you understand the relationships in your database. If your ID columns are named consistently these tools work better.
So, here's an example about how to do the steps numbered 2 and 3 in your question with a single JOIN query.
SELECT p.patient_id p.name, v.visit_id, rx.drug_name, rx.drug_dose
FROM patients AS p
LEFT JOIN visits AS v ON p.patient_id = v.patient_id
LEFT JOIN prescription AS rx ON v.visit_id = rx.visit_id
WHERE p.patient_id = '100'
ORDER BY p.patient_id, v.visit_id, rx.prescription_id
Like all SQL queries, this returns a virtual table of rows and columns. In this case each row of your virtual table has patient, visit, and drug data. I used LEFT JOIN in this example. That means that a patient with no visits will have a row with NULL data in it. If you specify JOIN MySQL will omit those patients from the virtual table.
My application has a facebook-like stream that displays updates of various types. So it will show regular posts (from the "posts" table), and events (from the "events" tables) table and so on.
The problem is I have no idea how to fetch these records from different tables since they have different columns. Shall I query the database multiple times and then organize the data in PHP? if so, how? I'm not sure how I should approach this.
Your help is much appreciated :)
Unless the events and post are related to each other, then you'd probably query them separately, even if they show up on the same page.
You're not going to want to use JOIN just for the sake of it. Only if there is a foreign key relationship. If you don't know what that is, then you don't have one.
If the data tables are related to each other you can generally get the data back in a single query using some combination of JOINs and UNIONs. For a better answer, however, you'll have to post the structure of your data tables and a sample of what (combined) records you need for the website.
If you don't know the columns, you can get the table meta-data and find out what the columns represent and their corresponding data types.
If you know which columns, you can select from the multiple tables or even use nested selects or joins to get the data out.
Ideally you'd simply use a JOIN to obtain data from multiple tables in one query. However, without knowing more about your table schemas it's hard to provide any useful specifics. (It most likely won't be possible unless you've factored this in from the beginning that said.)
As such, you might also want to create a generic "meta" table that provides information for each of the posts/events in a common format, and provides a means to link to the relevant table. (i.e.: It would contain the "parent" type and ID.) You could then use this meta table as the source for the "updates" stream and drill down to the approriate content as required.
Join the tables on user_id i.e.
Select * from posts p
left join status_updates su on p.user_id = su.user_id
limit 25;
or if your tables differ too much then play with a temporary table first
create table tmp_updates
(
select user_id, p.id as update_id, 'post' as update_type, p.text from posts;
);
insert into table tmp_updates
(
select user_id, su.id as update_id, 'status' as update_type, su.text from status_updates;
);
Select * from tmp_updates
where user_id = '...'
limit 25;
I have a question related to a web app that I developed in PHP, MYSQL.
basically part 1 is :
I display results in the form of table say for software testing.
ID Prod_Name Set Date Result Platform
1 Alpha1 Pro1 01.01.01 PASS 2.3.1.2_OS
Now, I have divided the tables accordingly
Table Name: Results
ID, Name, Date, Result
Table Name : Set
ID, Set_Name, Prod_name
Table Name : Platform
ID, Platform_Name, Set_Name
Now, ID in each table is an incremented value and does not relate to anything else.
My php app, starts with fetching the results from 'Results' table. Since I want SET to be displayed for every row, I am making an another connection to the database and using the query
select Set_name
from Set
where Prod_name = row['Name'] // row['Name'] is fetched from the results table.
now I also want to display platform which I am extracting it from Platform table using the above method i.e making another connection and passing Set_Name = row['Set_Name'] from the Set table.
Now for my application is there any other way to achieve the same result ?
Typically, for large web based applications, if data is coming from a database server is making multiple connection to a DB server a feasible option?
Please do not consider the fact that with MySQL declaring a connection statement once will do the needful but what about MSSQL server? Do we need to write a long sql statement with several joins/selfjoins/unions and use those variables all over the application?
How is the application design for this case will be?
Can anyonce give me some ideas please?
Thanks.
For pretty much any flavour of database, a single SELECT statement which joins three tables will perform better than three separate statements querying a table apiece. Joining is what relational databases do.
I may not have understood everything, but here is something similar. First, let's make an ER model.
Now, because you don't seem to like joins, create a view in the database.
CREATE VIEW v_test AS
SELECT TestID, ProductName, TestName, Date, Result, PlatformName
FROM Product AS p
JOIN Test AS t ON t.ProductID = p.ProductID
JOIN Platform AS f ON f.PlatformID = t.PlatformID;
With this in place, you can simply use:
SELECT * FROM v_test WHERE ProductName = 'Alpha1'
You may also take a look at this question/answer with a similar scenario.