I have 4 tables, I would like to select one column from each table, but only if the department has both 'Mick' and 'Dave working in it (must have both names, not one or the other). But it does not seem to be working properly:
SELECT SCHOOL_NAME, TOWN, COUNTY
FROM STUDENTS
NATURAL JOIN SCHOOLS NATURAL JOIN TOWNS NATURAL JOIN
COUNTIES
WHERE FIRST_NAME IN ('Mick','Dave)
/
I'm going wrong somewhere (probably lots of places :( ). Any help would be great
Don't use NATURAL JOIN. It is an abomination, because it does not take properly declared foreign key relationships into account. It only looks at the names of columns. This can introduce really hard to find errors.
Second, what you want is aggregation:
select sc.SCHOOL_NAME, t.TOWN, c.COUNTY
from STUDENTS st join
SCHOOLS sc
on st.? = sc.? join
TOWNS t
on t.? = ? join
COUNTIES c
on c.? = t.?
where FIRST_NAME in ('Mick', 'Dave')
group by sc.SCHOOL_NAME, t.TOWN, c.COUNTY
having count(distinct st.first_name) = 2;
The ? are placeholders for table and column names. If you are learning SQL, it is all the more important that you understand how columns line up for joins in different tables.
A where clause can only check the values in a single row. There is a separate row for each student, so there is no way -- with just a where -- to find both students. That is where the aggregation comes in.
You need at least three Join conditions, and properly end the string Dave with quote :
SELECT SCHOOL_NAME, TOWN, COUNTY
FROM SCHOOLS h
JOIN TOWNS t ON (t.id=h.town_id)
JOIN COUNTIES c ON (t.county_id=c.id)
WHERE EXISTS ( SELECT school_id
FROM STUDENTS s
WHERE s.first_name in ('Mick','Dave')
AND school_id = h.id
GROUP BY school_id
HAVING count(1)>1
);
SQL Fiddle Demo
You can use an analytic function in a sub-query to count the students who have the name Mick or Dave for each school_id (assuming that is your identifier for a school):
SELECT SCHOOL_NAME, TOWN, COUNTY
FROM ( SELECT *
FROM (
SELECT d.*,
COUNT(
DISTINCT
CASE WHEN FIRST_NAME IN ( 'Mick', 'Dave' ) THEN FIRST_NAME END
) OVER( PARTITION BY school_id )
AS num_matched
FROM STUDENTS d
)
WHERE num_matched = 2
)
NATURAL JOIN SCHOOLS
NATURAL JOIN TOWNS
NATURAL JOIN COUNTIES;
SQLFiddle
You would also be better to use an INNER JOIN and explicitly specify the join condition rather than relying on NATURAL JOIN.
I have 7 tables I am using in a view. For examples, I will be using these as my table names (The Fields within the table don't matter for this execpt that the PrimaryKey is tableName + ID)
Table 1.
Teacher
Table 2.
Student (Exception-- Student has all the ids in it, from all the other 6 tables)
Table 3.
Science
Table 4.
Math
Table 5.
History
Table 6.
German
Table 7.
Language Arts
Now, All the tables from 3-7 have a relationship to Student from Table 2. And Student has a relationship to teacher.
My view currently works if any of my tables have any fields. and some can be null, it also works if any of my tables 3-7 are completely null, it will still display.
However, my current problem is, if my teacher has no students assigned to them, making tables 2-7 null, empty, etc.... My query doesnt even return the teacher info that is filled in... First name, last name, Date of birth, etc.
How can I Accomplish this?
I tried doing all left joins from all the tables, since the teacher can have null fields, I tried doing an inner join from dbo.Teacher as Teacher Inner Join dbo.Student on dbo.Student.TeacherID = Teacher.TeacherID but that didnt work.. I am at a loss...
SELECT Teacher.TeacherID ,
Student.StudentID ,
Science.ScienceID ,
History.HistoryID ,
Math.MathID ,
German.GermanID ,
LanguageArts.LanguageArtsID
FROM dbo.Teacher AS Teacher
LEFT OUTER JOIN dbo.Student
ON dbo.Student.TeacherID = Teacher.TeacherID
LEFT OUTER JOIN dbo.Science AS Science
ON dbo.Student.ScienceID = Science.ScieneID
LEFT OUTER JOIN dbo.Math AS Math
ON dbo.Student.MathID = Math.MathID
LEFT OUTER JOIN dbo.History AS History
ON dboStudent.HistoryID = History.HistoryID
LEFT OUTER JOIN dbo.German AS German
ON dbo.Student.GermanID = German.GermanID
LEFT OUTER JOIN dbo.LanuageArts AS LanguageArts
ON dbo.Student.LanguageArtsID = LanguageArts.LanguageArtsID
Two comments:
Do you know the use of LEFT JOIN?. This query should return all teachers, even thouse with no students.
SELECT *
FROM teacher t LEFT JOIN student s ON s.teacher_id = t.id
(RIGHT JOIN would work if you want all student even if they do not have teachers)
Remmember that in SQL 1 == NULL and 1 != NULL are both false. So the following query will not result a teacher without students or a student without teachers.
SELECT *
FROM teacher t,
student s
WHERE s.teacher_id = t.id
I figured out my answer, in my select i was using dbo.Student.TeacherID, instead of dbo.Teacher.TeacherID, therefore my query was always coming back with null TeacherID values since I was checking my view with a query like this one
Select * from MyView Where TeacherID = 1;
This returned null since my select was pulling Student.TeacherID which is null, so I Swapped out dbo.Student.TeacherID for dbo.Teacher.TeacherID and it is now resolved.
Such a bleh moment. Thanks for comments and replies.!
As I am reading back in my OP, I said I was selecting
SELECT Teacher.TeacherID ,
Student.StudentID ,
which was technically a typo, but also my answer...
I'm trying to use sql query to show name_id and name attribute for all the people who have only grown tomato (veg_grown) and the result are show ascending order of name attribute.
CREATE TABLE people
(
name_id# CHAR(4) PRIMARY KEY,
name VARCHAR2(20) NOT NULL,
address VARCHAR2(80) NOT NULL,
tel_no CHAR(11) NOT NULL
)
CREATE TABLE area
(
area_id# CHAR(5) PRIMARY KEY,
name_id# REFRENCES people,
area_location_adress VARCHAR2(80) NOT NULL
)
CREATE TABLE area_use
(
area_id# REFERENCES area,
veg_grown VARCHAR (20) NOT NULL
)
but the veg_grown attribute has no relation to the people table but the people and area_use table are linked through area table so I tried using INNER JOIN like this which I confused my-self and didn't even work:
SELECT
name, name_id
FROM
people
INNER JOIN
area USING (name_id)
SELECT area_id
FROM area
INNER JOIN area_use USING (area_id)
WHERE veg_grown = 'tomato'
ORDER BY name ASC;
Surely there must be a way to select name_id and name who has only grown tomato in SQL query
I will take any help or advice :) thanks
SELECT p.name, p.name_id
FROM people p
JOIN area a
ON p.name_id = a.name_id
JOIN area_use au
ON a.area_id = au.area_id
AND au.veg_grown = 'tomato'
LEFT JOIN area_use au2
ON a.area_id = au2.area_id
AND au2.veg_grown <> 'tomato'
WHERE au2.area_id IS NULL;
This will use a LEFT JOIN to find people that only grow tomatoes. To find people that grow tomatoes and possibly anything else too, remove the LEFT JOIN part and everything below it.
An SQLfiddle to test with.
EDIT: If your field names contain # in the actual table, you'll need to quote the identifiers and add the #, I left them out in this sample.
AFAICT you only want entries where all info is available, so there are no left/right joins.
SELECT p.name_id, p.name
FROM people p
JOIN area a
ON p.name_id = a.name_id
JOIN area_use au
ON a.area_id = au.area_id
WHERE au.veg_grown = 'tomato'
ORDER BY p.name ASC
I'm not 100% sure of your data model, but this seems to be what you're trying to do.
SELECT name, people.name_id
FROM people, area, area_use
WHERE area.area_id = area_use.area_id
AND veg_grown = 'tomato'
AND area.name_id = people.name_id
ORDER BY name ASC;
I have this university task to create table using SELECT statement from multiple tables, but it's not as simple... here's basic info:
I'm using 2 tables -
CITY(city_ID, name);
PERSON(person_ID, name, surname, city_ID);
--city_ID is FK indicating in which city person was born.
Now my task is to create new table
STATISTICS(city_ID, city_name, number_of_births);
--number_of_births is basically a count of people born in each city
Problem is that I have to use only SELECT statement to do so.
I've tried something like this: (I'm well aware that this cannot possibly work but as to give you a better idea where I'm stuck)
CREATE TABLE Statistics AS
(SELECT city.city_ID, city.name as "city_name", number_of_births AS
(SELECT COUNT(*) FROM person WHERE person.city_id = city.city_id)
FROM city, person);
For SQL Server you can do SELECT * INTO. Something like this:
SELECT
*
INTO Statistics
FROM (
SELECT
city.city_ID,
city.name as "city_name",
(SELECT COUNT(*) FROM person WHERE person.city_id = city.city_id) as 'number_of_births'
FROM city
inner join person on city.city_id = person.city_id
) t1
(Posted on behalf of the question author).
Ok, this got really messy. Dave Zych's answer was correct when rewritten in Oracle dialect.
CREATE TABLE Statistics AS SELECT * FROM (
SELECT DISTINCT
city.city_ID,
city.name AS "City_name",
(SELECT COUNT(*) FROM person WHERE person.city_ID = city.city_ID) AS "number_of_births"
FROM city INNER JOIN person ON city.city_ID = person.city_ID);
I have a table where each row has a few fields that have ID's that relate to some other data from some other tables.
Let's say it's called people, and each person has the ID of a city, state and country.
So there will be three more tables, cities, states and countries where each has an ID and a name.
When I'm selecting a person, what's the easiest way to get the names of the city, state and country in a single query?
Note: I know this is possible with joins, however as there are more related tables, the nested joins makes the query hard to read, and I'm wondering if there is a cleaner way. It should also be possible for the person to have those fields empty.
Assuming the following tables:
create table People
(
ID int not null primary key auto_increment
,FullName varchar(255) not null
,StateID int
,CountryID int
,CityID int
)
;
create table States
(
ID int not null primary key auto_increment
,Name varchar(255) not null
)
;
create table Countries
(
ID int not null primary key auto_increment
,Name varchar(255) not null
)
;
create table Cities
(
ID int not null primary key auto_increment
,Name varchar(255) not null
)
;
With the Following Data:
insert into Cities(Name) values ('City 1'),('City 2'),('City 3');
insert into States(Name) values ('State 1'),('State 2'),('State 3');
insert into Countries(Name) values ('Country 1'),('Country 2'),('Country 3');
insert into People(FullName,CityID,StateID,CountryID) values ('Has Nothing' ,null,null,null);
insert into People(FullName,CityID,StateID,CountryID) values ('Has City' , 1,null,null);
insert into People(FullName,CityID,StateID,CountryID) values ('Has State' ,null, 2,null);
insert into People(FullName,CityID,StateID,CountryID) values ('Has Country' ,null,null, 3);
insert into People(FullName,CityID,StateID,CountryID) values ('Has Everything', 3, 2, 1);
Then this query should give you what you are after.
select
P.ID
,P.FullName
,Ci.Name as CityName
,St.Name as StateName
,Co.Name as CountryName
from People P
left Join Cities Ci on Ci.ID = P.CityID
left Join States St on St.ID = P.StateID
left Join Countries Co on Co.ID = P.CountryID
JOINS are the only way to really do this.
You might be able to change your schema, but the problem will be the same regardless.
(A City is always in a State, which is always in a Country - so the Person could just have a reference to the city_id rather than all three. You still need to join the 3 tables though).
There is no cleaner way than joins. If the fields are allowed to be empty, use outer joins
SELECT c.*, s.name AS state_name
FROM customer c
LEFT OUTER JOIN state s ON s.id = c.state
WHERE c.id = 10
According to the description of the schema that you have given you will have to use JOINS in a single query.
SELECT
p.first_name
, p.last_name
, c.name as city
, s.name as state
, co.name as country
FROM people p
LEFT OUTER JOIN city c
ON p.city_id = c.id
LEFT OUTER JOIN state s
ON p.state_id = s.id
LEFT OUTER JOIN country co
ON p.country_id = co.id;
The LEFT OUTER JOIN will allow you to fetch details of person even if some IDs are blank or empty.
Another way is to redesign your lookup tables. A city is always in a state and a state in a country. Hence your city table will have columns : Id, Name and state_id. Your state table will be : Id, Name and country_id. And country table will remain the same : Id and Name.
The person table will now have only 1 id : city_id
Now your query will be :
SELECT
p.first_name
, p.last_name
, c.name as city
, s.name as state
, co.name as country
FROM people p
LEFT OUTER JOIN city c
ON p.city_id = c.id
LEFT OUTER JOIN state s
ON c.state_id = s.id
LEFT OUTER JOIN country co
ON s.country_id = co.id;
Notice the difference in the last two OUTER JOINS
If the tables involved are reference tables (i.e. they hold lookup data that isn't going to change during the life time of a session), depending on the nature of your application, you could pre-load the reference data during you application start up. Then your query doesn't need to do the joins, instead it returns the id values, and in your application you do a decode of the ids when you need to display the data.
The easiest solution is to use the names as the primary keys in city, state, and country. Then your person table can reference them by the name instead of the pseudokey "id". That way, you don't need to do joins, since your person table already has the needed values.
It does take more space to store a string instead of a 4-byte pseudokey. But you may find the tradeoff worthwhile, if you are threatened by joins as much as you seem to be (which, by the way, is like a PHP programmer being reluctant to use foreach -- joins are fundamental to SQL in the same way).
Also there are many city names that appear in more than one state. So your city table should reference the state table and use these two columns as the primary key.
CREATE TABLE cities (
city_name VARCHAR(30),
state CHAR(2),
PRIMARY KEY (city_name, state),
FOREIGN KEY (state) REFERENCES states(state)
);
CREATE TABLE persons (
person_id SERIAL PRIMARY KEY,
...other columns...
city_name VARCHAR(30),
state CHAR(2),
country_name VARCHAR(30),
FOREIGN KEY (city_name, state) REFERENCES cities(city_name, state),
FOREIGN KEY (country_name) REFERENCES countries(country_name)
);
This just an example of the technique. Of course it's more complex than this, because you may have city names in more than one country, you may have countries with no states, and so on. The point is SQL doesn't force you to use integer pseudokeys, so use CHAR and VARCHAR keys where appropriate.
A disadvantage of standard SQL is the the return data needs to be in tabular format.
However some database vendors have added features that makes it possible to select data in non-tabular format. I don't know whether MySQL knows such features.
Create a view that does the Person, City, State, and Country joins for you. Then just reference the View in all other joins.
Something like:
CREATE VIEW FullPerson AS
SELECT Person.*, City.Name, State.Name, Country.Name
FROM
Person LEFT OUTER JOIN City ON Person.CityId = City.Id
LEFT OUTER JOIN State ON Person.StateId = State.Id
LEFT OUTER JOIN Country ON Person.CountryId = Country.Id
Then in other queries, you can
SELECT FullPerson.*, Other.Value
FROM FullPerson LEFT OUTER JOIN Other ON FullPerson.OtherId = Other.Id
All great answers but the questioner specified they didn't want to use joins. As one respondent demonstrated, assuming your Cities, States, and Countries tables have an Id and a Description field you might be able to do something like this:
SELECT
p.Name, c.Description, s.Description, ct.Description
FROM
People p, Cities c, States s, Countries ct
WHERE
p.Id = value AND
c.Id = value AND
s.Id = value AND
ct.Id = value;
Joins are the answer. With practise they will become more readable to you.
There may be special cases where creating a function would help you, for example you could do the following (in Oracle, I don't know any mysql):
You could create a function to return a formatted address given the city state and country codes, then your query becomes
SELECT first_name, last_name, formated_address(city_id, state_id, country_id)
FROM people
WHERE some_where_clause;
where formated_address does individual lookups on the city state and country tables and puts separators between the decoded values, or returns "no address" if they are all empty, etc