I'm trying to wrap my brain around a query and hoping you can help. I have two tables: a customer_table and a product_table that look like this
name sku_num1 sku_num2 sku_num3 sku_num4
----------------------------------------------------
Bob A B C D
Frank E A
Tom G
Shelly G E
Justin E G A
sku_num widget_name
-------------------
A widget_a
B widget_b
C widget_c
D widget_d
So what I want to do is return a list of all the customers who have at least 1 product whose SKU appears in the product table. So with the above information I would receive back the records for
Bob
Frank
Justin
Any ideas how to do this?
There is no need to join one table twice:
SELECT *
FROM customers
WHERE sku_num1 IN (SELECT sku_num
FROM product_table)
OR sku_num2 IN (SELECT sku_num
FROM product_table)
....
The reason why you need multiple conditions that do a full table scan on the product_table is your wrong database design. The products a customer bought should not go into multiple columns in the customer table. Instead you should have a third table that is a N:M relation between customer and products.
Does something like this not work?
select name
from customer c, products p
where ( c.sku_num1 = p.sku)
or ( c.sku_num2 = p.sku)
or ( c.sku_num3 = p.sku)
or ( c.sku_num4 = p.sku)
Christopher,
Does this mean that you are just looking for any customers where sku_num1 or sku_num2 or sku_num3 or sku_num4 is not null?
If that's the case, you could do it two different ways.
select * from customers
where sku_num1 is not null
or sku_num2 is not null
or sku_num3 is not null
or sku_num4 is not null
If you are trying to see if they have ordered something from a specific product list, you could modify this to:
select * from customers
where sku_num1 in (select sku_num from skus)
or sku_num2 in (select sku_num from skus)
or sku_num3 in (select sku_num from skus)
or sku_num4 in (select sku_num from skus)
Incidentally, this is why people normally don't structure tables like this. There should be another join table, for lack of anything better to call it, customer_skus which would tie together customers and skus and just have a customerID and a sku_num.
This would make the query easier to write, read, and maintain. The query would look something like:
select distinct name from customers, customer_skus, skus
where customers.id = customer_skus.id
and customer_skus.sku_num = skus.sku_num
You can join a table with itself by using an alias:
select * from mytable a, mytable b where condition
Related
I have two tables on Oracle database, one is named departments_table and the other is locations_table. The departments.table has dep_id, dep_name, location_id, staff_id, employer_id. The locations table consists of location_id, city_id, streetname_id and postcode_id. How do I calculate the number of departments that each location has?
This is the code below is what I have tried to replicate but have been unsuccessful. The error message below that is what shows once the code has submitted.
SELECT dep_name, location_id,
COUNT(*)
FROM departments_table
WHERE location_id => 1
GROUP BY dep_name;
The results of this is an error, " not a single group function "
If you want to count how many departments are in each location, then you must group by location, not by department name, right? Let's start with that.
Then, you don't need ANYTHING about the individual departments in the output of the query, do you? You just need the location id and the count of departments.
select location_id, count(*) as cnt
from departments_table
group by location_id
;
This does most of the work. You may want to add the location name (city, address, etc.), which is/are stored elsewhere - in the locations_table. So you will need a join. And there may be locations in that table that are not, in fact, the location of any department (their id doesn't appear in the departments_table at all). If so, you would need an OUTER join. Also for those departments you probably want to show a count of 0 (rather than null) - you can "fix" that with the nvl() function. So you will end up with something like
select l.*, nvl(g.cnt, 0) as department_count
from locations_table l
left outer join
( select location_id, count(*) as cnt
from departments_table
group by location_id
) g
on l.location_id = g.location_id
;
SELECT l.location_id, l.city, COUNT(d.DEPARTMENT_ID)
FROM OEHR_LOCATIONS l, OEHR_DEPARTMENTS d WHERE l.location_id = d.location_id
GROUP BY l.location_id, l.city ORDER BY l.city;
This method works. I created aliases and made minor changes. OEHR stands for the table names so ignore that.
I was just wondering how you select multiple records from a table column. Please see below the query.
SELECT DISTINCT DEPARTMENT_NAME, CITY, COUNTRY_NAME
FROM OEHR_DEPARTMENTS
NATURAL JOIN OEHR_EMPLOYEES
NATURAL JOIN OEHR_LOCATIONS
NATURAL JOIN OEHR_COUNTRIES
WHERE JOB_ID = 'SA_MAN' AND JOB_ID = 'SA_REP'
;
Basically, I want to be able to select records from the table column I have, however when you use AND it only displays SA_MAN and not SA_REP. I have also tried to use OR and it displays no rows selected. How would I actually be able to select both Job ID's without it just displaying one or the other.
Sorry this may sound like a stupid question (and probably not worded right), but I am pretty new to Oracle 11g SQL.
For your own comfort while debugging, I suggest you to use inner joins instead of natual joins.
That where clause is confusing, if not utterly wrong, because you don't make clear which tables' JOB_ID should be filtered. Use inner joins, give aliases to tables, and refer to those aliases in the where clause.
select distinct DEPARTMENT_NAME, CITY, COUNTRY_NAME
from OEHR_DEPARTMENTS t1
join OEHR_EMPLOYEES t2
on ...
join OEHR_LOCATIONS t3
on ...
join OEHR_COUNTRIES t4
on ...
where tn.JOB_ID = 'SA_MAN' AND tm.JOB_ID = 'SA_REP'
After rephrasing your query somehow like this, you'll have a clearer view on the logical operator you'll have to use in the where clause, which I bet will be an OR.
EDIT (after more details were given)
To list the departments that employ staff with both 'SA_MAN' and 'SA_REP' job_id, you have to join the departments table with the employees twice, once with the filter job_id='SA_MAN' and once with job_id='SA_REP'
select distinct DEPARTMENT_NAME, CITY, COUNTRY_NAME
from OEHR_DEPARTMENTS t1
join OEHR_EMPLOYEES t2
on t1.department_id = t2.department_id --guessing column names
join OEHR_EMPLOYEES t3
on t1.department_id = t3.department_id --guessing column names
join OEHR_LOCATIONS t4
on t1.location_id = t4.location_id --guessing column names
join OEHR_COUNTRIES t5
on t4.country_id = t5.country_id --guessing column names
where t2.job_id = 'SA_MAN' and t3.job_id = 'SA_REP'
order by 1, 2, 3
I have 2 tables, COMPANY and EMPLOYEE.
COMPANY_ID is the primary key of the COMPANY table and foreign key for EMPLOYEE table. The COMPANY_ID is a 10 digit number. We are generate a 3 number combination and query the database.
The select statement has regex to bulk load the company based on COMPANY_ID. The query is executed multiple times with different patterns
i.e.
regexp_like(COMPANY_ID, '^(000|001|002|003|004|005|006|007|008|009)') .
Existing query looks something like this -
select *
from COMPANY company
where regexp_like(company.COMPANY_ID, '^(000|001|002|003|004|005|006|007|008|009)')
The new requirement is to retrieve the company information along with the employee count. For example if a company has 10 employees, then the query should return all the columns of the COMPANY table, along with employee count i.e. 10
This is the select statement that I came up with -
select
nvl(count_table.cont_count, 0), company.*
from
COMPANY company,
(select company.COMPANY_ID, count(company.COMPANY_ID) as cont_count
from COMPANY company, EMPLOYEE employee
where regexp_like(company.COMPANY_ID, '^(000|001|002|003|004|005|006|007|008|009)')
and company.CONTACT_ID = employee.CONTACT_ID
group by (company.COMPANY_ID)) count_table
where
regexp_like(company.COMPANY_ID, '^(000|001|002|003|004|005|006|007|008|009)')
and count_table.COMPANY_ID(+)= company.COMPANY_ID
Above query works, but it takes double the time compared to the previous statement. Is there a better way to retrieve the employee count?
Note: Oracle database is in use.
You don't need to execute that expensive REGEXP_LIKE twice:
select nvl(count_table.cont_count,0),company.*
from COMPANY company
,( select employee.COMPANY_ID, count(employee.COMPANY_ID) as cont_count
from EMPLOYEE employee
group by (employee.COMPANY_ID)
) count_table
where regexp_like(company.COMPANY_ID, '^(000|001|002|003|004|005|006|007|008|009)')
and count_table.COMPANY_ID(+)= company.COMPANY_ID
Or you could use a scalar subquery:
select company.*
, (select count(*)
from employee e
where e.company_id = c.company_id
)
from COMPANY c
where regexp_like(c.COMPANY_ID, '^(000|001|002|003|004|005|006|007|008|009)')
And personally I would ditch the slow REGEXP_LIKE for something like:
where substr(c.company_id,1,3) between '000' and '009'
The derived table does not add value, thus I would get rid of it and use a scalar query (because I do not know all of your columns in the company table to properly do a group by):
select c.*,
nvl(
(select count(1)
from employee emp
where emp.company_id = c.company_id
),0) employee_count
from company c
where regexp_like(c.company_id, '^(000|001|002|003|004|005|006|007|008|009)')
Also, if performance is still an issue, I would consider modifying your where statement to not use a regexp.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Addendum
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I see that the question explicitly identifies that the employee table has company_id as a foreign key. Since this is clarified, I am removing this statement:
The data model for these tables is not intuitive (would you not have
company_id as a foreign key in the employees table?).
I would like the resultset that consists of the union of queries performed based on each row of an outer SELECT query. How do I do this?
As an example:
create table Person
(
Id int,
Age int
)
create table Movie
(
Id int,
Title varchar(500),
AgeRestriction int
)
I would like a resultset that shows me, for every person, which movies that person would be allowed to watch.
UPDATE: Ok, so as it turns out there is no "equivalent" of SelectMany in TSQL since the model is completely different, as the author of the correct answer has pointed out an inner join will do the job just fine.
Your question is pretty unclear but it sounds like you might want CROSS APPLY
Random Example
SELECT DISTINCT ca.* /*DISTINCT for UNION semantics*/
FROM master..spt_values v
CROSS APPLY (SELECT TOP 2 *
FROM sys.columns c
WHERE c.name > v.name
ORDER BY c.name) ca
Edit. Following clarification you just need a JOIN
SELECT P.Id,
M.Title
FROM Person P
JOIN Movie M
ON M.AgeRestriction <= P.Age
am a newbie to Oracle/PL SQL.I've 2 tables A and B.
A has a column CustId,Age,Location and Date. Table B has 2 columns CustId,CustName.
What would be the sql query to show show CustName and Location for a given age?
Thanks.
your question "What would be the sql query to show show CustName and Location for a given age?" helps define your query pretty well:
SELECT CustName, Location
FROM TableA a
INNER JOIN TableB b
ON b.CustId = a.CustId
WHERE a.Age = #
All we need to do on top of that select for your specific fields is make sure to join the two tables on their common column (CustID).
Another option would be to avoid the WHERE statement:
SELECT CustName, Location
FROM TableB b
INNER JOIN TableA a
ON a.CustID = b.CustID
AND a.Age = #
you need join. something like
SELECT custname, location FROM a JOIN b ON a.custid = b.custid WHERE age = [age];