I am working on a project and for my login credentials checking process I am trying to create a view in which the name,surname,username and password of customers,workers and admins are stored so that I can search faster and I have two questions.
Do you think it is a good idea to do that ?
If yes, can you help me how to do that?
Thank you in advance.
1) yes, but for simplicity rather than performance (and a few other reasons)
2) CREATE OR REPLACE VIEW viewname AS your_select_statement;
If the front-end is a single interface for both customers and employees then the tables should not be separated in the first place. If you have a person who is both a customer and a worker then they would appear on two tables and it is possible the data would not be synchronized between the two and if you create a view then they would appear twice. Instead create a single table for all people and have separate tables for data specific to customers, workers and admins.
Something like:
People
id | firstname | surname | username | password_hash | password_salt
--------------------------------------------------------------------
1 | alice | abbot | aa | abc | 123
2 | bob | barnes | bb | def | 456
3 | charlotte | carol | cc | ghi | 789
4 | daniel | david | dd | jkl | 036
Customers
id | Credit_Limit | has_Trade_Account
-------------------------------------
2 | 0 | 0
3 | 2000 | 1
Workers
id | Joining_Date | Grade
--------------------------
1 | 2015-01-01 | 5
3 | 2000-12-25 | 3
Admins
id | Edit_Permissions
----------------------
3 | Orders
3 | Stock
Related
I'm working on my senior High School Project and am reaching out to the community for help! (As my teacher doesn't know the answer to my question).
I have a simple "Products" table as shown below:
I also have a "Orders" table shown below:
Is there a way I can create a field in the "Orders" table named "Total Cost", and make that automaticly calculate the total cost from all the products selected?
Firstly, I would advise against storing calculated values, and would also strongly advise against using calculated fields in tables. In general, calculations should be performed by queries.
I would also strongly advise against the use of multivalued fields, as your images appear to show.
In general, when following the rules of database normalisation, most sales databases are structured in a very similar manner, containing with the following main tables (amongst others):
Products (aka Stock Items)
Customers
Order Header
Order Line (aka Order Detail)
A good example for you to learn from would be the classic Northwind sample database provided free of charge as a template for MS Access.
With the above structure, observe that each table serves a purpose with each record storing information pertaining to a single entity (whether it be a single product, single customer, single order, or single order line).
For example, you might have something like:
Products
Primary Key: Prd_ID
+--------+-----------+-----------+
| Prd_ID | Prd_Desc | Prd_Price |
+--------+-----------+-----------+
| 1 | Americano | $8.00 |
| 2 | Mocha | $6.00 |
| 3 | Latte | $5.00 |
+--------+-----------+-----------+
Customers
Primary Key: Cus_ID
+--------+--------------+
| Cus_ID | Cus_Name |
+--------+--------------+
| 1 | Joe Bloggs |
| 2 | Robert Smith |
| 3 | Lee Mac |
+--------+--------------+
Order Header
Primary Key: Ord_ID
Foreign Keys: Ord_Cust
+--------+----------+------------+
| Ord_ID | Ord_Cust | Ord_Date |
+--------+----------+------------+
| 1 | 1 | 2020-02-16 |
| 2 | 1 | 2020-01-15 |
| 3 | 2 | 2020-02-15 |
+--------+----------+------------+
Order Line
Primary Key: Orl_Order + Orl_Line
Foreign Keys: Orl_Order, Orl_Prod
+-----------+----------+----------+---------+
| Orl_Order | Orl_Line | Orl_Prod | Orl_Qty |
+-----------+----------+----------+---------+
| 1 | 1 | 1 | 2 |
| 1 | 2 | 3 | 1 |
| 2 | 1 | 2 | 1 |
| 3 | 1 | 1 | 4 |
| 3 | 2 | 3 | 2 |
+-----------+----------+----------+---------+
You might also opt to store the product description & price on the order line records, so that these are retained at the point of sale, as the information in the Products table is likely to change over time.
I am very new to database design and am using MS Access to try achieve my task. I am trying to create a database design that will allow for the name and description of two items to be queried
on a single row of information. Here is the problem: certain items are converted to other particular items -
any item can have multiple conversions performed on it, and all conversions will have two (many) items involved.
In this sense, we have a many-to-many relationship which necessitates the use of an intermediate table. My
tables must be structured in a way that allows for me to, in one row, query the Item ID's and names
of which items were involved in conversions.
My current table layout is as follows:
Items
+--------+----------+------------------+--+
| ItemID*| ItemName | ItemDescription | |
+--------+----------+------------------+--+
| 1 | DESK | WOOD, 4 LEG | |
| 2 | SHELF | WOOD, SOLID BASE | |
| 3 | TABLE | WOOD, 4 LEG | |
+--------+----------+------------------+--+
ItemConversions
+------------------+--------------+
| ConversionID(CK) | Item1_ID(CK) |
+------------------+--------------+
| 1 | 2 |
| 2 | 2 |
| 3 | 1 |
+------------------+--------------+
Conversions
+---------------+----------+----------+
| ConversionID* | Item1_ID | Item2_ID |
+---------------+----------+----------+
| 1 | 2 | 1 |
| 2 | 2 | 3 |
| 3 | 1 | 3 |
+---------------+----------+----------+
What I want is for it to be possible to achieve the kind of query I described above, though I don't think
my current layout is going to work for this, since the tables are only being joined on Item1_ID. Any advice
would be appreciated, hopefully my tables are not too specific and this is easily understandable.
A sample query output might look like this:
+--------------+----------+----------+----------+----------+
| ConversionID | Item1_ID | ItemName | Item2_ID | ItemName |
+--------------+----------+----------+----------+----------+
| 1 | 2 | SHELF | 1 | DESK |
+--------------+----------+----------+----------+----------+
I got it working how I wanted to with the help of June7's suggestion - I didn't know you could add in tables
multiple times in the query design page (very useful!). As for the tables, I edited the layout so that I have only
Items and Conversions (I deleted ItemConversions). Using the AS sql command I was able to write a query that pulls
the data I want from the tables. The table and query layout can be seen below:
Items
+--------+----------+------------------+--+
| ItemID*| ItemName | ItemDescription | |
+--------+----------+------------------+--+
| 1 | DESK | WOOD, 4 LEG | |
| 2 | SHELF | WOOD, SOLID BASE | |
| 3 | TABLE | WOOD, 4 LEG | |
+--------+----------+------------------+--+
Conversions
+---------------+----------+----------+
| ConversionID* | Item1_ID | Item2_ID |
+---------------+----------+----------+
| 1 | 2 | 1 |
| 2 | 2 | 3 |
| 3 | 3 | 1 |
+---------------+----------+----------+
Query:
SELECT
Conversions.ConversionID,
Conversions.Item1_ID,
Conversions.Item2_ID,
Items.ItemName,
Items_1.ItemName,
FROM
(
Conversions
INNER JOIN
Items
ON Conversions.Item1_ID = Items.ItemID
)
INNER JOIN
Items AS Items_1
ON Conversions.Item2_ID = Items_1.ItemID;
Sorry, I'm very new to SQL. I just learned it few hours ago. I'm using MariaDB + InnoDB Engine with HeidiSQL software + CodeIgniter 3. Let's say I have a table named disciples with the following data:
-------------------
| sort_id | name |
-------------------
| 1 | Peter |
| 4 | John |
| 3 | David |
| 5 | Petrus |
| 2 | Matthew |
-------------------
I'm fully aware that it's better to have a column called sort_id to be able to fetch the data using ORDER BY if I prefer a custom sorting. But if I delete row 3, the new table will look like this:
-------------------
| sort_id | name |
-------------------
| 1 | Peter |
| 4 | John |
| 5 | Petrus |
| 2 | Matthew |
-------------------
The thing is I'm having OCD (imagine there are 1000 rows), it hurts my eyes to see this mess with some missing numbers (in this case number 3 - see the above table) under sort_id. I think it has something to do with "relational database". Is there a way to quickly and automatically "re-assign/reset" new sort_id numbers to given rows and sort them ASC order according to the name using SQL code without having to do it manually?
-------------------
| sort_id | name |
-------------------
| 1 | John |
| 2 | Matthew |
| 3 | Peter |
| 4 | Petrus |
-------------------
I figured this out after reading the answer from Lynn Crumbling.
She made me realized I need a primary key in order to have a better management for my rows which is exactly what I was looking for. It happens that InnoDB automatically creates a primary key and is hidden from HeidiSQL interface unless I specify a specific column for example id. Now, I can re-organize my table rows by editing the primary key id and the table row will automatically sort itself the way I want. Before this, I edited the sort_id but the data did not update accordingly because it was not the primary key.
------------------------
| id | sort_id | name |
------------------------
| 1 | 1 | Peter |
| 2 | 4 | John |
| 3 | 5 | Petrus |
| 4 | 2 | Matthew |
------------------------
Thank you.
I have a table with information like this.
ID | Name | #ofCow | UItem | place
--------+---------+-------- +---------+----------
0 | Bob | 7 | 1 | maine
1 | Bob | 3 | 5 | new york
2 | Tom | 2 | 5 | cali
I wish to produce a table like this where it would add up the number of cows and Uitem if the name is the same. However my select query seems to not be working. I suspect it is because the place column is the problem. Since you can't add 'Maine' and 'New York' together. Can anyone help me find a solution ?
ID | Name | #ofCow | UItem |
--------+---------+-------- +---------+
0 | Bob | 10 | 6 |
2 | Tom | 2 | 5 |
TLDR : Add the values in two columns in table 1 if name is same. Output in another column. Don't show the two columns. I don't need places also.
You could use this (I have considered the name of the table as HolyCow) :
SELECT holy.ID,
holy.Name,
SUM(holy.Cows) as '#ofCow',
SUM(holy.UItem) as 'UItem'
FROM HolyCow holy
GROUP BY holy.ID, holy.Name
ORDER BY holy.Name
Hope this helps!!
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I have spent hours researching how to write the proper SQL for the following task, and finally I feel that I have to get some help as this is the most complex SQL query I have ever had to write :(
I am putting together an email list with all the email adresses that we have on our customers.
I have two tables: one customer table that contains customer level information, and one contact person table that contains person level information. Most of the data is overlapping, so the same email adress will occure in both tables. But the email adress field can be empty in both tables, and I do not want to return any empty rows.
Users that buy in our physical store are often only registered in the customer level table, but users that buys online are always registered both in the customer level table and the person level table.
I want to create a full list where I get all email adresses, where all email adresses are unique, no email adresses are duplicates and no email adresses are null.
Also I want to join in columns from the customer table when the data is retrieved from the person table (the zip code in my example below).
Customers
| CustomerID | Firstname | Lastname | Email | Zipcode |
| 22 | Jeff | Carson | jeffcar#mail.com | 81712 |
| 29 | John | Doe | null | 51211 |
| 37 | Gina | Andersen | null | 21147 |
| 42 | Brad | Cole | brad#company.org | 39261 |
Contact persons
| PersonID | CustomerID | Firstname | Lastname | Email |
| 8712 | 22 | Jeff | Carson | null || 8916 | 29 | Jane | Doe | jane#doe.net || 8922 | 29 | Danny | Doe | null |
| 9181 | 37 | Gina | Andersen | gina#gmail.com |
| 9515 | 37 | Ben | Andersen | ben88#gmail.com |
I want to join the tables to generate the following:
Final table
| PersonID | CustomerID | Firstname | Lastname | Email | Zipcode |
| 8712 | 22 | Jeff | Carson | jeffcar#mail.com | 81712 |
| 8916 | 29 | Jane | Doe | jane#doe.net | 51211 |
| 9181 | 37 | Gina | Andersen | gina#gmail.com | 21147 |
| 9515 | 37 | Ben | Andersen | ben88#gmail.com | 21147 |
| null | 42 | Brad | Cole | brad#company.org | 39261 |
I guessed this would be a fairly common task to do, but I haven't found anyone with a similar question, so I put my trust in the expertise out there.
This SQL will get you exactly the results table you were looking for. I've made a live demo you can play with here at SQLFiddle.
SELECT
ContactPerson.PersonID,
Customer.CustomerID,
COALESCE(ContactPerson.FirstName, Customer.FirstName) AS FirstName,
COALESCE(ContactPerson.LastName, Customer.LastName) AS LastName,
COALESCE(ContactPerson.Email, Customer.Email) AS Email,
Customer.ZipCode
FROM Customer
LEFT JOIN ContactPerson
ON ContactPerson.CustomerID = Customer.CustomerID
WHERE COALESCE(ContactPerson.Email, Customer.Email) IS NOT NULL
Results (identical to your desired results):
| PersonID | CustomerID | FirstName | LastName | Email | ZipCode |
| 8712 | 22 | Jeff | Carson | jeffcar#mail.com | 81712 |
| 8916 | 29 | Jane | Doe | jane#doe.net | 51211 |
| 9181 | 37 | Gina | Andersen | gina#gmail.com | 21147 |
| 9515 | 37 | Ben | Andersen | ben88#gmail.com | 21147 |
| NULL | 42 | Brad | Cole | brad#company.org | 39261 |
A quick explanation of some key points to aid understanding:
The query uses a LEFT JOIN to join the two tables together. JOINs are pretty common once you get into SQL problems like this. I won't go into an in-depth explanation here: now that you know what they are called you should have no trouble Googling for loads of info on them!
NB: COALESCE basically means 'the first one of these options which isn't null' (docs). So this query will grab their name and email address from ContactPerson IF POSSIBLE, otherwise from Customer. If NEITHER of these tables hold an email address, then the WHERE clause makes sure that record isn't included at all, as required.
This will work:
SELECT b.PersonID
,a.CustomerID
,a.FirstName
,a.LastName
,COALESCE(a.Email,b.Email) AS Email
,a.ZipCode
FROM Customers a
LEFT JOIN Contact b
ON a.CustomerID = b.CustomerID
WHERE COALESCE(a.Email, b.Email) IS NOT NULL
Demo: SQL Fiddle
select con.personid,
con.customerid,
con.firstname,
con.lastname,
coalesce(con.email, cus.email) email,
cus.zipcode
from contact_persons con
right join
customers cus
on con.customerid = cus.customerid