Every derived table needs an alias - sql

Question

Here's my code, I need the Full names and salaries of faculty with lowest salary from every department. My subquery works on it's own, but I can't get the rest to work together.
SELECT CONCAT(FName,' ',LName) AS 'Faculty',DepartmentID,Salary
FROM Faculty,
(SELECT DISTINCT DepartmentID AS 'Department', MIN(Salary) AS 'MinSalary'
FROM Faculty GROUP BY DepartmentID)
WHERE Faculty.DepartmentID= 'Department' AND Salary= 'MinSalary'
ORDER BY DepartmentID

Answer 1

you need to pud alias on your subquery
SELECT CONCAT(FName,' ',LName) AS 'Faculty',DepartmentID,Salary
FROM Faculty,
(
SELECT DISTINCT DepartmentID AS 'Department',
MIN(Salary) AS 'MinSalary'
FROM Faculty GROUP BY DepartmentID
) xx -- <<< this is the alias. (Don't forget this)
WHERE Faculty.DepartmentID= 'Department' AND Salary= 'MinSalary'
ORDER BY DepartmentID
xx is the name of your subquery in the example above. (and I think the query is not giving you the results you want)
To modify your query for better performance, (Assuming you are using MYSQL because of CONCAT function)
SELECT CONCAT(a.FName,' ',a.LName) AS FacultyName,
a.DepartmentID,
a.Salary
FROM Faculty a
INNER JOIN
(
SELECT DepartmentID ,
MIN(Salary) AS MinSalary
FROM Faculty
GROUP BY DepartmentID
) xx -- <<< this is the alias.
ON a.DepartmentID = xx.DepartmentID AND
a.Salary = xx.MinSalary
-- WHERE .. (add extra condition here)
ORDER BY DepartmentID
SQLFiddle Demo
UPDATE 1
It might also be SQL Server 2012. (already supports CONCAT())
SELECT CONCAT([FName], ' ',[LName]) FullName, [DepartmentID], [Salary]
FROM
(
SELECT [FName], [LName], [DepartmentID], [Salary],
ROW_NUMBER() OVER (partition BY DepartmentID
ORDER BY Salary) rn
FROM Faculty
) x
WHERE x.rn = 1
SQLFiddle Demo

Answer 2

As the error message in the title hints, Standard SQL requires sub-queries in the FROM clause to have names. You should also learn to use the JOIN notation, not the comma-separated list of table names. You need to know the old (pre-SQL92) notation to recognize it; you should not use it yourself.
SELECT CONCAT(F.FName, ' ', F.LName) AS 'Faculty', F.DepartmentID, F.Salary
FROM Faculty AS F
JOIN (SELECT DISTINCT DepartmentID AS 'Department', MIN(Salary) AS 'MinSalary'
FROM Faculty
GROUP BY Department) AS D
ON F.DepartmentID = D.Department AND F.Salary = D.MinSalary
ORDER BY F.DepartmentID;

Answer 3

Better to use aliases for both table and the subselect query table:
SELECT CONCAT(F.FName,' ',F.LName) AS Faculty,F.DepartmentID, F.Salary
FROM Faculty F,
(SELECT DISTINCT DepartmentID AS Department, MIN(Salary) AS MinSalary
FROM Faculty GROUP BY DepartmentID) AS DEP_MIN_SALARY
WHERE F.DepartmentID= DEP_MIN_SALARY.Department
AND F.Salary= DEP_MIN_SALARY.MinSalary
ORDER BY FDepartmentID;
One observation: You are not retrieving any columns from the derived table. Hope that is intentional.

Answer 4

SELECT CONCAT(F.FName,' ',F.LName) AS Faculty, F.DepartmentID, F.Salary
FROM Faculty F
JOIN (
SELECT DepartmentID,
MIN(Salary) AS MinSalary
FROM Faculty
GROUP BY DepartmentID
) G
ON F.DepartmentID = G.DepartmentID AND F.Salary = G.MinSalary
ORDER BY F.DepartmentID
The problem with using single-quotes around alias names is that you fall into the trap evident in your query - your first WHERE condition is matching DepartmentID against the string literal 'Department'. This goes too for the 'MinSalary' column.
Of note also is the fact that GROUP BY does not need DISTINCT - because you are already getting distinct values of DepartmentID.
And to the first problem that brought you here - each derived table (aka sub-query) needs an alias, or something with which to identify the columns from it. In the example below, you can see that the first part of the ON clause compares two DepartmentID columns. The aliases F and G are imperative here to distinguish between the two, hence the requirement to alias each table.

Answer 5

Your query needs an alias for subquery
select
concat(F.FName, ' ', F.LName) as Faculty,
F.DepartmentID,
D.MinSalary
from faculty as F
inner join
(
select T.DepartmentID, min(T.Salary) as MinSalary
from Faculty as T
group by T.DepartmentID
) as D on D.DepartmentID = F.DepartmentID and D.MinSalary = F.Salary
order by F.DepartmentID

Answer 6

Your derived table needs a name which is what the error message is complaining about (see YouNeedToPutATableAliasHere below):
SELECT CONCAT(FName,' ',LName) AS Faculty,DepartmentID,Salary
FROM Faculty,
(SELECT DISTINCT DepartmentID AS Department, MIN(Salary) AS MinSalary
FROM Faculty GROUP BY DepartmentID) AS YouNeedToPutATableAliasHere
WHERE Faculty.DepartmentID= 'Department' AND Salary= MinSalary
ORDER BY DepartmentID
Note I've also removed some single-quotes where they didn't make sense to me. (Perhaps you meant double-quotes, square brackets, or backticks for column names, but single quotes probably won't work - you may need to do the same for 'Department'?)
You will also be creating a Cartesian join unless you specify conditions correlating the two tables. A better query for "faculty with the minimum salary in the dept 'Department'" might be (note I have removed the redundant GROUP BY):
SELECT CONCAT(FName,' ',LName) AS Faculty,F.DepartmentID,F.Salary
FROM Faculty F
INNER JOIN (
SELECT DepartmentID,
MIN(Salary) AS MinSalary
FROM Faculty
GROUP BY DepartmentID
) AS MinSal ON MinSal.DepartmentID = F.DepartmentID
AND F.Salary = MinSal.MinSalary
WHERE F.DepartmentID= 'Department'
ORDER BY F.DepartmentID
Or, since you are only selecting the one department 'Department', you could do:
SELECT CONCAT(FName,' ',LName) AS Faculty,F.DepartmentID,F.Salary
FROM Faculty F
WHERE F.DepartmentID= 'Department'
AND F.Salary = (
SELECT MIN(Salary)
FROM Faculty
WHERE DepartmentID = F.DepartmentID
)
Or even (which would also work for multiple departments but may be slower than a join):
SELECT CONCAT(FName,' ',LName) AS Faculty,F.DepartmentID,F.Salary
FROM Faculty F
WHERE F.DepartmentID= 'Department'
AND NOT EXISTS(
SELECT 1
FROM Faculty FF
WHERE FF.DepartmentID = F.DepartmentID
AND FF.Salary < F.Salary
)
In fact, in looking at your original query and in an effort to make this question complete while reading #RichardTheKiwi's comments, I will incorporate that interpretation into this answer. This assumes you are using MySQL (from the CONCAT function) and that you meant backticks instead of forward ticks for column names. It also assumes you wanted the minimum-salaried faculty for every department, not just the specified one as 'Department'. It just requires a small change from my first suggested query though - namely the removal of the WHERE clause:
SELECT CONCAT(FName,' ',LName) AS Faculty,F.DepartmentID,F.Salary
FROM Faculty F
INNER JOIN (
SELECT DepartmentID,
MIN(Salary) AS MinSalary
FROM Faculty
GROUP BY DepartmentID
) AS MinSal ON MinSal.DepartmentID = F.DepartmentID
AND F.Salary = MinSal.MinSalary
ORDER BY F.DepartmentID