I'm looking for help with acquiring and displaying information from related tables in MySQL. I have two tables:
"table1" with columns id, name, surname
"table2" with columns id, phone
They are related by the id columns.
I'm trying to display the name, surname and phone together. What I'm currently using is:
SELECT name, surname, phone FROM table1, table2 WHERE table1.id = table2.id
However, I feel like I'm not using the relationship between the tables properly as I believe this would work between unrelated tables as well.
Also, not every id from table1 has a record in table2, meaning not everyone has a phone number. The method above results in only showing those id's that exist in both table1 and table2, while I want to display the data of those without a phone number as well, either by a blank space or a "N/A" in the phone column.
Any tips on how to properly display the data are greatly appreciated.
You need to use an LEFT OUTER JOIN statement to join the two tables together. LEFT OUTER JOIN will still show records from table1 even if there is no matching id in table2. Something like:
SELECT
table1.name,
table1.surname,
table2.phone
FROM table1
LEFT OUTER JOIN table2
ON table1.id = table2.id
More info: https://www.w3schools.com/sql/sql_join_left.asp
Related
I have to export a csv file for the orders, but these informations for one order are stored in different tables.. So I have the name of a buyer in a table and what he bought in another table and I have to export in a single row for my csv file..
It's something like this
table1: entity_id, billing_name, created_at, grand_total, status
table2:
sku, name, price, base_price, original_price, tax_percent,
tax_amount, discount_percent, discount_amount, price_incl_tax, order_id
table1.entity_id=table2.order_id (is the way I can GROUP BY)
the export part it's clear for me...I just don't knoow how to combine these information to create a row
Thank you for your help!
Based on the information provided, here is a query that returns the columns mentioned.
You need to JOIN the two tables together, you can do this using JOIN table2 t2 ON t2.order_id = t1.entity_id where these tables also have an alias of t1 and t2. JOIN info can be seen here
Additionally, it is possible to alias these columns for the purpose of changing the column names for your CSV client using t1.grand_total AS total
SELECT
t1.entity_id,
t1.billing_name,
t1.created_at,
t1.grand_total,
t1.status,
t2.sku,
t2.name,
t2.price,
t2.base_price,
t2.original_price,
t2.tax_percent,
t2.tax_amount,
t2.discount_percent,
t2.discount_amount,
t2.price_incl_tax,
t2.order_id
FROM
table1 t1
JOIN table2 t2 ON t2.order_id = t1.entity_id
I'm creating a website where the user can add some information about multiple computers into a database.
In the mysql database I have 3 tables. TypeOfMachine, Software and Hardware. The only common thing they have is the NumberOfMachine.
I must create a page where the user can run reports showing devices that have a specific piece of software installed (user specified) or specific hardware (user specified) after he submitted the computer's info.
Any ideas how I can do this?
And how I can connect all 3 tables into one?
I thought about this code but i dont know what to put in WHERE. I have 10 variables. and I have to show all the computers with what the user has asked and their info as well!
$search1 = "
SELECT
TypeOfMachine.NumberOfMachine, TypeOfMachine.TypeOfMachine, TypeOfMachine.OS, Software.Software1, Software.Software2, Software.Software3, Hardware.SSD, Hardware.Harddisk, Hardware.MonitorSize, Hardware.Ram, Hardware.Rom, Hardware.Processor
FROM TypeOfMachine, Software, Hardware
WHERE
but i
You want to use a join. This example is based on the fact that you've said the NumberOfMachine field is present in all tables and is a common link between them:
SELECT
TypeOfMachine.NumberOfMachine,
TypeOfMachine.TypeOfMachine,
TypeOfMachine.OS,
Software.Software1,
Software.Software2,
Software.Software3,
Hardware.SSD,
Hardware.Harddisk,
Hardware.MonitorSize,
Hardware.Ram,
Hardware.Rom,
Hardware.Processor
FROM TypeOfMachine
LEFT JOIN Software
ON Software.NumberOfMachine = TypeOfMachine.NumberOfMachine
LEFT JOIN Hardware
ON Hardware.NumberOfMachine = TypeOfMachine.NumberOfMachine
WHERE
...
It's general question, I don't know which tables contains a spesific columns as indicator for all tables. It's about inner and outer join:
The two common types of joins are an inner join and an outer join. The difference between an inner and outer join is in the number of rows included in the results table.
Inner join: The results table produced by an inner join contains only rows that existed in both tables.
Outer join: The combined table produced by an outer join contains all rows that existed in one table with blanks in the columns for the rows that did not exist in the second table.
For instance, if table1 contains a row for Joe and a row for Sally, and table2 contains only a row for Sally, an inner join would contain only one row: the row for Sally. However, an outer join would contain two rows — a row for Joe and a row for Sally — even though the row for Joe would have a blank field for weight.
The results table for the outer join contains all the rows for one table. If any of the rows for that table don’t exist in the second table, the columns for the second table are empty. Clearly, the contents of the results table are determined by which table contributes all its rows, requiring the second table to match it.
Two kinds of outer joins control which table sets the rows and which must match: a LEFT JOIN and a RIGHT JOIN.
You use different SELECT queries for an inner join and the two types of outer joins. The following query is an inner join:
SELECT columnnamelist FROM table1,table2
WHERE table1.col2 = table2.col2
And these queries are outer joins:
SELECT columnnamelist FROM table1 LEFT JOIN table2
ON table1.col1=table2.col2
SELECT columnnamelist FROM table1 RIGHT JOIN table2
ON table1.col1=table2.col2
In all three queries, table1 and table2 are the tables to be joined. You can join more than two tables. In both queries, col1 and col2 are the names of the columns being matched to join the tables. The tables are matched based on the data in these columns. These two columns can have the same name or different names, but they must contain the same type of data.
For general concept you can use #Scrowler suggestion, or this one:
http://stackoverflow.com/questions/1204217/mysql-select-join-3-tables
I'm having some trouble figuring out how I should build my database for this project i'm currently working on. Fishing-related.
I'm just not sure how to set up my tables.
Table 1(ID, username, email etc)
Table 2(fish, weight, length etc)
How do i join these two tables? Should I have a column named ID in the 2nd table aswell? Because I need to know which user uploaded what fish. I'm just not sure how to do that.
Any help is appreciated.
Yes you have to, and that is called Relation Databases this is example
Users (UserID, UserName, Password)
Fish (FishID, UserID, FishName, Length, Weight)
and then you connect them using UserID
select u.UserName, f.FishName, f.Length, f.Weight
from Users u
LEFT JOIN Fish f on (f.UserID=u.UserID)
and if you are looking for specific user then just add at the end
WHERE u.UserID=#UserID
Looking at you're table structure I think it's best to change the id name in table 1 to *user_id* and add a column in the second table also named *user_id*. Joining using the columns is then very simple using the following query:
SELECT *
FROM table1
JOIN table2 USING (user_id)
Other possibility would be to add a column named *user_id* (or something else) to table2 and create a query like:
SELECT *
FROM table1
JOIN table2 ON table2.user_id = table1.id
In this case, you set the columns to use for the join in the 'ON .. = ..' structure.
I am LEFT JOINing multiple tables as such:
SELECT * FROM table1
LEFT JOIN table2 ON table1.id = table2.fid
LEFT JOIN table3 ON table1.id = table3.fid
LEFT JOIN table4 ON table1.id = table4.fid
LEFT JOIN table5 ON table1.id = table5.fid
LEFT JOIN table6 ON table1.id = table6.fid
WHERE table2.id = '5184'
Reason being is simply because I tried regular JOIN and no results are returned unless at least one record exists in tables1-6 which is often not the case. As it stands this returns the info I want, but the problem is that a lot of the field names repeat and when I do a 'mysql_fetch_array()' in PHP it hides any field with a duplicate name.
What type of query can I do to avoid this? At the very least, how do I construct the query such that it doesn't include all the double fields which are NULL?
Thanks
I can't help but notice that you aren't selecting anything from your left joined tables. It's my understanding that joins are typically used to pull data from secondary tables where something in those tables matches a field in the primary table. I pulled this example from W3 schools:
SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo
FROM Persons
LEFT JOIN Orders
ON Persons.P_Id=Orders.P_Id
ORDER BY Persons.LastName
And unless this is a typo, you are selecting everything from table 1 where an id column = 5186 in table 2.
You state that your query returns the info you want, but with many nulls and overwritten values. To fix this, I would restructure your query to follow the typical format shown above, and make sure you have a proper use of the left join statement.
EDIT AFTER OP COMMENTS:
You are naming a row id from table2, so I assume you should start by pulling fid from table 2 where table2.id = 5186, then left join from the other tables where table1.id = table2.fid.
SELECT table2.fid, table1.id, table3.id, [add other tables here, and revise field names to select the ones you want]
FROM table2
LEFT JOIN table1 ON table1.id = table2.fid
LEFT JOIN table 3 ON table3.fid = table1.id
[add left joins to other tables here]
WHERE table2.id = '5186'
If this doesn't help, I suggest being more specific towards what information the tables hold, and what you are searching for. A little more detail may help us help you.
select * from table1 join table2 on table1.column3=table2.column4 where ...
...
$row=mysql_fetch_assoc($result);
However, there are two columns in the new table(table1 join table2) which have the same column name, how to get the values of both respectively?
Call the columsn out specifically with an alias like
SELECT table_1.id as table_1_id, table_2.id as table_2_id
Youll have to list out all or most of the columns form at least one of the tables this way but you can get access to cols with the same name across multiple tables.
Prefix the column name in the select with its table name.
select table1.my_column, table2.my_column
from table1, table2
where table1.id = table2.t1_id
But with this method, you would have to read the columns using their returned order indexes, rather than their names. Another answer mentioned using as to name each column, so consider that if you're going to read them by name.
When there's a column name collision due to a query joining 2+ tables, you can not use *. You can use:
SELECT table_1.*,
table_2.*
FROM table_1,
table_2
If that doesn't return the list of columns you want, you will have to explicitly list every column. There's no way around - it's an all or nothing deal.
Table Aliases
...but typing out the full table name every time can be a pain, which is why you can alias tables:
SELECT t1.*,
t2.*
FROM table_1 AS t1,
table_2 t2
Either alias notation is supported. They're also required if you want to join a table to itself.
Using only the column names in a Select list that you actually need\ is always the best, but when you want everything, then, well, go ahead and use the *:
Select a.*,
b.*,
a.id as a_id,
b.id as b_id,
a.name as a_name,
b.name as b_name
from tablea a,
tableb b
...
It won't hurt to be redundant, as a.* includes a_id and a_name, but there values from the * get lost in the associative array, so just put them back in with new, unique names.