I have a table that contains all the transaction information
(transaction date, customer name, transaction amount, unit amount, store ID).
How to create a table which could properly show the stores that customer has visited? The customer could make purchase from multiple stores, so the relationship between customer and store should be one to many. I am trying to check the stores each customer had visited.
Example:
Transaction table
store_ID
transaction_date
customer_name
transaction_amount
transaction_unit
Expected Output
customer_name
store_list
This is just a Hypothesis problem. Maybe list all shopped store seprately could be better? (But I guess it might create chaos if we want to check customer who made purchase in those stores). Thanks in advance :)
Since you already have a table with all information needed, maybe you are asking for a view, to avoid denormalized/duplicated data.
Example is shown below. Here I will use sqlite syntax (text instead of varchar, etc). We are normalizing data to avoid problems - for example you have shown a table with customer names, but different customers can have the same name, so we use customer_id instead.
First the tables:
create table if not exists store (id integer primary key, name text, address text);
create table if not exists customer (id integer, name text, document integer);
create table if not exists unit (symbol text primary key);
insert into unit values ('USD'),('EUR'),('GBP'); -- static data
create table if not exists transact (id integer primary key, store_id integer references store(id), customer_id integer references customer(id), transaction_date date, amount integer, unit text references unit(symbol));
-- transaction is a reserved word, so transact was used instead
Now the view:
-- store names concatenated with ',' using sqlite's group_concat
create view if not exists stores_visited as select cust.name, group_concat(distinct store.name order by store.id) from transact trx join customer cust on trx.customer_id=cust.id join store on trx.store_id=store.id group by cust.name order by cust.id;
-- second version, regular select with multiple lines
-- create view if not exists stores_visited as select cust.id, cust.name, store.id, store.name from transact trx join customer cust on trx.customer_id=cust.id join store on trx.store_id=store.id;
Sample data:
insert into store values
(1,'store one','address one'),
(2,'store two','address two')
(3,'store three','address three');
insert into customer values
(1,'customer one','custdoc one'),
(2,'customer two','custdoc two'),
(3,'customer three','custdoc three');
insert into transact values
(1,1,1,date('2021-01-01'),1,'USD'),
(2,1,1,date('2021-01-02'),1,'USD'),
(3,1,2,date('2021-01-03'),1,'USD'),
(5,1,3,date('2021-01-04'),1,'USD'),
(6,2,1,date('2021-01-05'),1,'USD'),
(7,2,3,date('2021-01-06'),1,'USD'),
(8,3,2,date('2021-01-07'),1,'USD');
Testing:
select * from stores_visited;
-- customer one|store one,store one,store two
-- customer three|store one,store two
-- customer two|store one
Related
I am learning SQL (postgres) and am trying to insert a record into a table that references records from two other tables, as foreign keys.
Below is the syntax I am using for creating the tables and records:
-- Create a person table + insert single row
CREATE TABLE person (
pname VARCHAR(255) NOT NULL,
PRIMARY KEY (pname)
);
INSERT INTO person VALUES ('personOne');
-- Create a city table + insert single row
CREATE TABLE city (
cname VARCHAR(255) NOT NULL,
PRIMARY KEY (cname)
);
INSERT INTO city VALUES ('cityOne');
-- Create a employee table w/ForeignKey reference
CREATE TABLE employee (
ename VARCHAR(255) REFERENCES person(pname) NOT NULL,
ecity VARCHAR(255) REFERENCES city(cname) NOT NULL,
PRIMARY KEY(ename, ecity)
);
-- create employee entry referencing existing records
INSERT INTO employee VALUES(
SELECT pname FROM person
WHERE pname='personOne' AND <-- ISSUE
SELECT cname FROM city
WHERE cname='cityOne
);
Notice in the last block of code, where I'm doing an INSERT into the employee table, I don't know how to string together multiple SELECT sub-queries to get both the existing records from the person and city table such that I can create a new employee entry with attributes as such:
ename='personOne'
ecity='cityOne'
The textbook I have for class doesn't dive into sub-queries like this and I can't find any examples similar enough to mine such that I can understand how to adapt them for this use case.
Insight will be much appreciated.
There doesn’t appear to be any obvious relationship between city and person which will make your life hard
The general pattern for turning a select that has two base tables giving info, into an insert is:
INSERT INTO table(column,list,here)
SELECT column,list,here
FROM
a
JOIN b ON a.x = b.y
In your case there isn’t really anything to join on because your one-column tables have no column in common. Provide eg a cityname in Person (because it seems more likely that one city has many person) then you can do
INSERT INTO employee(personname,cityname)
SELECT p.pname, c.cname
FROM
person p
JOIN city c ON p.cityname = c.cname
But even then, the tables are related between themselves and don’t need the third table so it’s perhaps something of an academic exercise only, not something you’d do in the real world
If you just want to mix every person with every city you can do:
INSERT INTO employee(personname,cityname)
SELECT pname, cname
FROM
person p
CROSS JOIN city c
But be warned, two people and two cities will cause 4 rows to be inserted, and so on (20 people and 40 cities, 800 rows. Fairly useless imho)
However, I trust that the general pattern shown first will suffice for your learning; write a SELECT that shows the data you want to insert, then simply write INSERT INTO table(columns) above it. The number of columns inserted to must match the number of columns selected. Don’t forget that you can select fixed values if no column from the query has the info (INSERT INTO X(p,c,age) SELECT personname, cityname, 23 FROM ...)
The following will work for you:
INSERT INTO employee
SELECT pname, cname FROM person, city
WHERE pname='personOne' AND cname='cityOne';
This is a cross join producing a cartesian product of the two tables (since there is nothing to link the two). It reads slightly oddly, given that you could just as easily have inserted the values directly. But I assume this is because it is a learning exercise.
Please note that there is a typo in your create employee. You are missing a comma before the primary key.
I didn't find a working solution for creating a "lookup column" in a Firebird database.
Here is an example:
Table1: Orders
[OrderID] [CustomerID] [CustomerName]
Table2: Customers
[ID] [Name]
When I run SELECT * FROM ORDERS I want to get OrderID, CustomerID and CustomerName....but CustomerName should automatically be computed by looking for the "CustomerID" in the "ID" column of "Customer" Table, returning the content of the "Name" column.
Firebird has calculated fields (generated always as/computed by), and these allow selecting from other tables (contrary to an earlier version of this answer, which stated that Firebird doesn't support this).
However, I suggest you use a view instead, as I think it performs better (haven't verified this, so I suggest you test this if performance is important).
Use a view
The common way would be to define a base table and an accompanying view that gathers the necessary data at query time. Instead of using the base table, people would query from the view.
create view order_with_customer
as
select orders.id, orders.customer_id, customer.name
from orders
inner join customer on customer.id = orders.customer_id;
Or you could just skip the view and use above join in your own queries.
Alternative: calculated fields
I label this as an alternative and not the main solution, as I think using a view would be the preferable solution.
To use calculated fields, you can use the following syntax (note the double parentheses around the query):
create table orders (
id integer generated by default as identity primary key,
customer_id integer not null references customer(id),
customer_name generated always as ((select name from customer where id = customer_id))
)
Updates to the customer table will be automatically reflected in the orders table.
As far as I'm aware, the performance of this option is less than when using a join (as used in the view example), but you might want to test that for yourself.
FB3+ with function
With Firebird 3, you can also create calculated fields using a trigger, this makes the expression itself shorter.
To do this, create a function that selects from the customer table:
create function lookup_customer_name(customer_id integer)
returns varchar(50)
as
begin
return (select name from customer where id = :customer_id);
end
And then create the table as:
create table orders (
id integer generated by default as identity primary key,
customer_id integer not null references customer(id),
customer_name generated always as (lookup_customer_name(customer_id))
);
Updates to the customer table will be automatically reflected in the orders table. This solution can be relatively slow when selecting a lot of records, as the function will be executed for each row individually, which is a lot less efficient than performing a join.
Alternative: use a trigger
However if you want to update the table at insert (or update) time with information from another table, you could use a trigger.
I'll be using Firebird 3 for my answer, but it should translate - with some minor differences - to earlier versions as well.
So assuming a table customer:
create table customer (
id integer generated by default as identity primary key,
name varchar(50) not null
);
with sample data:
insert into customer(name) values ('name1');
insert into customer(name) values ('name2');
And a table orders:
create table orders (
id integer generated by default as identity primary key,
customer_id integer not null references customer(id),
customer_name varchar(50) not null
)
You then define a trigger:
create trigger orders_bi_bu
active before insert or update
on orders
as
begin
new.customer_name = (select name from customer where id = new.customer_id);
end
Now when we use:
insert into orders(customer_id) values (1);
the result is:
id customer_id customer_name
1 1 name1
Update:
update orders set customer_id = 2 where id = 1;
Result:
id customer_id customer_name
1 2 name2
The downside of a trigger is that updating the name in the customer table will not automatically be reflected in the orders table. You would need to keep track of these dependencies yourself, and create an after update trigger on customer that updates the dependent records, which can lead to update/lock conflicts.
No need here a complex lookup field.
No need to add a persistant Field [CustomerName] on Table1.
As Gordon said, a simple Join is enough :
Select T1.OrderID, T2.ID, T2.Name
From Customers T2
Join Orders T1 On T1.IDOrder = T2.ID
That said, if you want to use lookup Fields (as we do it on a Dataset) with SQL you can use some thing like :
Select T1.OrderID, T2.ID,
( Select T3.YourLookupField From T3 where (T3.ID = T2.ID) )
From Customers T2 Join Orders T1 On T1.IDOrder = T2.ID
Regards.
Basically I'm trying to create a database schema based around multiple unrelated tables that will not need to reference each other AFAIK.
Each table will be a different "category" that will have the same columns in each table - name, date, two int values and then a small string value.
My issue is that each one will need to be "updated" daily, but I want to keep a record of the items for every single day.
What's the best way to go about doing this? Would it be to make the composite key the combination of the date and the name? Or use something called a "trigger"?
Sorry I'm somewhat new to database design, I can be more specific if I need to be.
Yes, you have to create a trigger for each category table
I'm assuming name is PK for each table? If isnt the case, you will need create a PK.
Lets say you have
table categoryA
name, date, int1, int2, string
table categoryB
name, date, int1, int2, string
You will create another table to store changes log.
table category_history
category_table, name, date, int1, int2, string, changeDate
You create two trigger, one for each category table
Where you save what table gerate the update and what time was made.
create trigger before update for categoryA
INSERT INTO category_history VALUES
('categoryA', OLD.name, OLD.date, OLD.int1, Old.int2, OLD.string, NOW());
This is pseudo code, you need write trigger using your rdbms syntaxis, and check how get system date now().
As has already been pointed out, it is poor design to have different identical tables for each category. Better would be a Categories table with one entry for each category and then a Dailies table with the daily information.
create table Categories(
ID smallint not null auto_generated,
Name varchar( 20 ) not null,
..., -- other information about each category
constraint UQ_Category_Name unique( Name ),
constraint PK_Categories( ID )
);
create table Dailies(
CatID smallint not null,
UpdDate date not null,
..., -- Daily values
constraint PK_Dailies( CatID, UpdDate ),
constraint FK_Dailies_Category foreign key( CatID )
references Categories( ID )
);
This way, adding a new category involves inserting a row into the Categories table rather than creating an entirely new table.
If the database has a Date type distinct from a DateTime -- no time data -- then fine. Otherwise, the time part must be removed such as by Oracle's trunc function. This allows only one entry for each category per day.
Retrieving all the values for all the posted dates is easy:
select C.Name as Category, d.UpdDate, d.<daily values>
from Categories C
join Dailies D
on D.CatID = C.ID;
This can be made into a view, DailyHistory. To see the complete history for Category Cat1:
select *
from DailyHistory
where Name = 'Cat1';
To see all the category information as it was updated on a specific date:
select *
from DailyHistory
where UpdDate = date '2014-05-06';
Most queries will probably be interested in the current values -- that is, the last update made (assuming some categories are not updated every day). This is a little more complicated but still very fast if you are worried about performance.
select C.Name as Category, d.UpdDate as "Date", d.<daily values>
from Categories C
join Dailies D
on D.CatID = C.ID
and D.UpdDate =(
select Max( UpdDate )
from Dailies
where CatID = D.CatID );
Of course, if every category is updated every day, the query is simplified:
select C.Name as Category, d.UpdDate as "Date", d.<daily values>
from Categories C
join Dailies D
on D.CatID = C.ID
and D.UpdDate = <today's date>;
This can also be made into a view. To see today's (or the latest) updates for Category Cat1:
select *
from DailyCurrent
where Name = 'Cat1';
Suppose now that updates are not necessarily made every day. The history view would show all the updates that were actually made. So the query shown for all categories as they were on a particular day would actually show only those categories that were actually updated on that day. What if you wanted to show the data that was "current" as of a particular date, even if the actual update was several days before?
That can be provided with a small change to the "current" query (just the last line added):
select C.Name as Category, d.UpdDate as "Date", d.<daily values>
from Categories C
join Dailies D
on D.CatID = C.ID
and D.UpdDate =(
select Max( UpdDate )
from Dailies
where CatID = D.CatID
and UpdDate <= date '2014-05-06' );
Now this shows all categories with the data updated on that date if it exists otherwise the latest update made previous to that date.
As you can see, this is a very flexible design which allows access the data just about any way desired.
I have a data processor that would create a table from a select query.
<_config:table definition="CREATE TABLE TEMP_TABLE (PRODUCT_ID NUMBER NOT NULL, STORE NUMBER NOT NULL, USD NUMBER(20, 5),
CAD NUMBER(20, 5), Description varchar(5), ITEM_ID VARCHAR(256), PRIMARY KEY (ITEM_ID))" name="TEMP_TABLE"/>
and the select query is
<_config:query sql="SELECT DISTINCT ce.PRODUCT_ID, ce.STORE, op.USD ,op.CAD, o.Description, ce.ITEM_ID
FROM PRICE op, PRODUCT ce, STORE ex, OFFER o, SALE t
where op.ITEM_ID = ce.ITEM_ID and ce.STORE = ex.STORE
and ce.PRODUCT_ID = o.PRODUCT_ID and o.SALE_ID IN (2345,1234,3456) and t.MEMBER = ce.MEMBER"/>
When I run that processor, I get an unique constraint error, though I have a distinct in my select statement.
I tried with CREATE TABLE AS (SELECT .....) its creating fine.
Is it possible to get that error? I'm doing a batch execute so not able to find the individual record.
The select distinct applies to the entire row, not to each column individually. So, two rows could have the same value of item_id but be different in the other columns.
The ultimate fix might be to have a group by item_id in the query, instead of select distinct. That would require other changes to the logic. Another possibility would be to use row_number() in a subquery and select the first row.
I created a table that contains information about a company. One attribute is their telephone number. A company can have many telephone numbers.
How do I create multi-valued attributes in SQL?
In a separate table like:
CREATE TABLE Company
(
Id int identity primary key,
Name nvarchar(100) not null UNIQUE --UNIQUE is optional
)
GO
CREATE TABLE CompanyPhones
(
Id int identity primary key,
Phone nvarchar(100) not null,
CompanyId int NOT NULL REFERENCES Company(Id) ON DELETE CASCADE
)
How to use these structures:
SELECT CompanyPhones.Phone
FROM Company
JOIN CompanyPhones
ON Company.Id = CompanyPhones.CompanyId
WHERE Company.Name=N'Horns and Hoogs Ltd.'
There is generally no such thing as multi-valued attribute in relational databases.
Possible solutions for your problem:
Create a separate table for storing phone numbers which references your company table by primary key and contains undefinite number of rows per company.
For example, if you have table company with fields id, name, address, ... then you can create a table companyphones with fields companyid, phone.
(NOT recommended in general, but if you only need to show a list of phones on website this might be an option) Storing telephones in a single field using varchar(...) or text and adding separators between numbers.
In addition to Oleg and Sergey's answers, a third option might be to create multiple phone fields on the company table - for example, as SwitchboardPhone and FaxNumber for the main switchboard and the fax line, respectively.
This type of solution is generally regarded as a form of denormalisation, and is generally only suitable where there is a small number of multiple options, each with a clearly defined role.
So, for example, this is quite a common way to represent landline and mobile/cellphone numbers for a contact list table, but would be thoroughly unsuitable for a list of all phone extensions within a company.
There're some possibilities in different implementations of RDBMS.
For example, in PostgreSQL you can use array or hstore or even JSON (in 9.3 version):
create table Company1 (name text, phones text[]);
insert into Company1
select 'Financial Company', array['111-222-3333', '555-444-7777'] union all
select 'School', array['444-999-2222', '555-222-1111'];
select name, unnest(phones) from Company1;
create table Company2 (name text, phones hstore);
insert into Company2
select 'Financial Company', 'mobile=>555-444-7777, fax=>111-222-3333'::hstore union all
select 'School', 'mobile=>444-999-2222, fax=>555-222-1111'::hstore;
select name, skeys(phones), svals(phones) from Company2
sql fiddle demo
You can also create indexes on these fields - https://dba.stackexchange.com/questions/45820/how-to-properly-index-hstore-tags-column-to-faster-search-for-keys, Can PostgreSQL index array columns?
In SQL Server, you can use xml datatype to store multivalues:
create table Company (name nvarchar(128), phones xml);
insert into Company
select 'Financial Company', '<phone type="mobile">555-444-7777</phone><phone>111-222-3333</phone>' union all
select 'School', '<phone>444-999-2222</phone><phone type="fax">555-222-1111</phone>'
select
c.name,
p.p.value('#type', 'nvarchar(max)') as type,
p.p.value('.', 'nvarchar(max)') as phone
from Company as c
outer apply c.phones.nodes('phone') as p(p)
sql fiddle demo
You can also create xml indexes on xml type column.