I have a table that contains data like below:
Name
ID
Dept
Joe
1001
Accounting
Joe
1001
Marketing
Mary
1003
Administration
Mary
1009
Accounting
Each row is uniquely identified with a combo of Name and ID. I want the resulting table to combine rows that have same Name and ID and put their dept's together separated by a comma in alpha order. So the result would be:
Name
ID
Dept
Joe
1001
Accounting, Marketing
Mary
1003
Administration
Mary
1009
Accounting
I am not sure how to approach this. So far I have this, which doesn't really do what I need:
SELECT Name, ID, COUNT(*)
FROM employees
GROUP BY Name, ID
I know COUNT(*) is irrelevant here, but I am not sure what to do. Any help is appreciated! By the way, I am using PostgreSQL and I am new to the language.
Apparently there is an aggregate function for string concatenation with PostgreSQL. Find documentation here. Try the following:
SELECT Name, ID, string_agg(Dept, ', ' ORDER BY Dept ASC) AS Departments
FROM employees
GROUP BY Name, ID
Related
I have an application filter which can generate duplicate SQL queries to the result SQL like:
select * from articles
inner join users on articles.users_id = users.id
inner join users on articles.users_id = users.id
where users.name like %xxx%
The question is if a database is able to handle these duplicates or not. What happened in the database if this query comes inside? If I should remove it from the result SQL or if I can leave it as is.
This is a self join.
A self join is a regular join, but the table is joined with itself.
Example
SELECT
A.Id,
A.FullName,
A.ManagerId,
B.FullName as ManagerName
FROM Employees A
JOIN Employees B
ON A.ManagerId = B.Id
A and B are different table aliases for the same table.
The self join, as its name implies, joins a table to itself. To use a self join, the table must contain a column (call it X) that acts as the primary key and a different column (call it Y) that stores values that can be matched up with the values in Column X. The values of Columns X and Y do not have to be the same for any given row, and the value in Column Y may even be null.
Let’s take a look at an example. Consider the table Employees:
Id
FullName
Salary
ManagerId
1
John Smith
10000
3
2
Jane Anderson
12000
3
3
Tom Lanon
15000
4
4
Anne Connor
20000
5
Jeremy York
9000
1
Each employee has his/her own Id, which is our “Column X.” For a given employee (i.e., row), the column ManagerId contains the Id of his or her manager; this is our “Column Y.” If we trace the employee-manager pairs in this table using these columns:
The manager of the employee John Smith is the employee with Id 3,
i.e., Tom Lanon.
The manager of the employee Jane Anderson is the employee with Id 3,
i.e., Tom Lanon.
The manager of the employee Tom Lanon is the employee with Id 4,
i.e., Anne Connor.
The employee Anne Connor does not have a manager; her ManagerId is
null.
The manager of the employee Jeremy York is the employee with Id 1,
i.e., John Smith.
This type of table structure is very common in hierarchies. Now, to show the name of the manager for each employee in the same row, we can run the following query:
SELECT
employee.Id,
employee.FullName,
employee.ManagerId,
manager.FullName as ManagerName
FROM Employees employee
JOIN Employees manager
ON employee.ManagerId = manager.Id
which returns the following result:
Id
FullName
ManagerId
ManagerName
1
John Smith
3
Tom Lanon
2
Jane Anderson
3
Tom Lanon
3
Tom Lanon
4
Anne Connor
5
Jeremy York
1
John Smith
The query selects the columns Id, FullName, and ManagerId from the table aliased employee. It also selects the FullName column of the table aliased manager and designates this column as ManagerName. As a result, every employee who has a manager is output along with his/her manager’s ID and name.
In this query, the Employees table is joined with itself and has two different roles:
Role 1: It stores the employee data (alias employee).
Role 2: It stores the manager data (alias manager).
By doing so, we are essentially considering the two copies of the Employees table as if they are two distinct tables, one for the employees and another for the managers.
You can find more about the concept of the self join in our article "An illustrated guide to the SQL self join".
I am new in SQL and have problem picking the biggest value of a column for every manager_id and also other information in the same row.
Let me show the example - consider this table:
name
manager_id
sales
John
1
100
David
1
80
Selena
2
26
Leo
1
120
Frank
2
97
Sara
2
105
and the result I am expecting would be like this:
name
manager_id
top_sales
Leo
1
120
Sara
2
105
I tried using Max but the problem is that I must group it with manager_id and not being able to take name of the salesPerson.
select manager_id, max(sales) as top_sales
from table
group by manager_id ;
This is just an example and the actual query is very long and I am taking the information from different tables. I know that I can use the same table and join it again but the problem is as I mentioned this query is very long as I am extracting info from different tables with multiple conditions. And I don't want to make a temporary table to save it. It should be done in one single query and I actually did solve this but the query is super long due to the inner join that I used and made original table twice.
My question is that can I use Max and have the value in the name column or is there other method to solve this?
Appreciate all help
You can use row_number() with CTE to get the highest sales for each manager as below:
with MaxSales as (
select name, manager_id, sales,row_number() over (partition by manager_id order by sales desc) rownumber from table
)
select name , manager_id ,sales from MaxSales where rownumber=1
I have 2 tables - one master and the other lookup. both don't have any keys. The structure of the tables is below.
first name last name role location Compensation Level state
john smith Manager LA A CA
john smith Manager BOS B MA
super smither developer LA B CA
tina taylor supervisor SFO A CA
tina taylor supervisor BOS B MA
first name last name role dept
john smith manager finance
john smith manager hr
super smither developer PA
tina taylor supervisor HR
tina taylor supervisor hr
very understandably, joining the two tables to get the dept for a first name, last name and role combination will result in incorrect results since there are other fields involved in the mix which identify a true unique record.
But given a structure like this, is there any way i can join the two tables to get the dept?
Using an inline subquery is not an option due to the way the final procedure is designed and due to other factors.
Any thoughts on this?
Expected output:
first name last name role location Compensation state dept
john smith Manager LA A CA finance
john smith Manager BOS B MA hr
super smither developer LA B CA PA
tina taylor supervisor SFO A CA HR
tina taylor supervisor BOS B MA HR
Here's an example that gives deterministic results, but they're arbitrary results. It's simply bases on determining an "ordered position" in each table, so that a choice can be made, and that choice be the same every time the query is executed, but there is no way to know that the choice is the correct one.
WITH
sorted_t1 AS
(
SELECT
*,
ROW_NUMBER() OVER (PARTITION BY first_name, last_name, role
ORDER BY compensation_level, location, state) AS discriminator
FROM
t1
)
,
sorted_t2 AS
(
SELECT
*,
ROW_NUMBER() OVER (PARTITION BY first_name, last_name, role
ORDER BY dept) AS discriminator
FROM
t2
)
SELECT
*
FROM
sorted_t1 t1
FULL OUTER JOIN
sorted_t2 t2
ON t1.first_name = t2.first_name
AND t1.last_name = t2.last_name
AND t1.role = t2.role
AND t1.discriminator = t2.discriminator
NOTES:
This assumes a "case-insensitive" collation sequence. Otherwise the john smith rows will never join (as 'Manager' wouldn't match 'manager')
Similarly, the two tina taylor rows in table 2 are different ('hr' vs 'HR'), but if the collation sequence is case-insensitive it doesn't matter which gets joined to which, as there is no "material" difference between the rows.
It's also worth noting that in the example above there is no Real Reason to assume that the 'John Smith' from LA is in finance. The query simply forces that association because or the ORDER BY chosen in the ROW_NUMBER(). This means that when using this technique you really should be using other fields, one's that mean something in relation to each other.
I'm using DB2 which apparently doesn't let you use the GROUP BY clause when it's returning more than one column. I have records that have repeating values for ID and name, for example:
EmpID | - name - | code
___________________________________
111111 | Williams | 1
---------------------------------
111111 | Williams | 2
----------------------------------
111112 | Davis | 3
---------------------------------
111113 | Gomez | 1
----------------------------------
111113 | Gomez | 3
----------------------------------
(Excuse my formatting) I need to get a single instance of each employee with a code (doesn't matter which code instance gets omitted as long as one shows up per employee).
Normally I could do:
SELECT * FROM employees GROUP BY EmpID;
DB2 doesn't let you do this for some reason. It says " The grouping is inconsistent." You can do:
SELECT EmpID from employees GROUP BY EmpID;
but if you introduce more return values then it gives you the error.
I tried looking into using a subquery and derived tables but I'm not sure how to compose it to select only one code value and exclude the records with a repeating employee value. If anyone has an answer or could point me to another thread that addresses this problem I would appreciate it very much.
It is required in most databases to GROUP BY each column in the SELECT list that is not in an aggregate function that is why you received an error message.
For your situation if it does not matter what code value is returned, then you can use an aggregate function and group by:
SELECT EmpID, name, MIN(code) code
FROM employees
GROUP BY EmpID, name;
See Demo
The group by is applied to both the EmpId and name, while the aggregate function is applied to the code column.
Note that due to that EmpID and name are functionally dependent on each other (as far as we can see from the sample you posted and the "repeating values" comment), the following two queries will return the same, identical results as the above query:
--- GROUP BY EmpID
------------------
SELECT EmpID, MIN(name) name, MIN(code) code
FROM employees
GROUP BY EmpID;
--- GROUP BY name
-----------------
SELECT MIN(EmpID) EmpID, name, MIN(code) code
FROM employees
GROUP BY name;
I have an Access database that has two tables that are related by PK/FK. Unfortunately, the database tables have allowed for duplicate/redundant records and has made the database a bit screwy. I am trying to figure out a SQL statement that will fix the problem.
To better explain the problem and goal, I have created example tables to use as reference:
alt text http://img38.imageshack.us/img38/9243/514201074110am.png
You'll notice there are two tables, a Student table and a TestScore table where StudentID is the PK/FK.
The Student table contains duplicate records for students John, Sally, Tommy, and Suzy. In other words the John's with StudentID's 1 and 5 are the same person, Sally 2 and 6 are the same person, and so on.
The TestScore table relates test scores with a student.
Ignoring how/why the Student table allowed duplicates, etc - The goal I'm trying to accomplish is to update the TestScore table so that it replaces the StudentID's that have been disabled with the corresponding enabled StudentID. So, all StudentID's = 1 (John) will be updated to 5; all StudentID's = 2 (Sally) will be updated to 6, and so on. Here's the resultant TestScore table that I'm shooting for (Notice there is no longer any reference to the disabled StudentID's 1-4):
alt text http://img163.imageshack.us/img163/1954/514201091121am.png
Can you think of a query (compatible with MS Access's JET Engine) that can accomplish this goal? Or, maybe, you can offer some tips/perspectives that will point me in the right direction.
Thanks.
The only way to do this is through a series of queries and temporary tables.
First, I would create the following Make Table query that you would use to create a mapping of the bad StudentID to correct StudentID.
Select S1.StudentId As NewStudentId, S2.StudentId As OldStudentId
Into zzStudentMap
From Student As S1
Inner Join Student As S2
On S2.Name = S1.Name
Where S1.Disabled = False
And S2.StudentId <> S1.StudentId
And S2.Disabled = True
Next, you would use that temporary table to update the TestScore table with the correct StudentID.
Update TestScore
Inner Join zzStudentMap
On zzStudentMap.OldStudentId = TestScore.StudentId
Set StudentId = zzStudentMap.NewStudentId
The most common technique to identify duplicates in a table is to group by the fields that represent duplicate records:
ID FIRST_NAME LAST_NAME
1 Brian Smith
3 George Smith
25 Brian Smith
In this case we want to remove one of the Brian Smith Records, or in your case, update the ID field so they both have the value of 25 or 1 (completely arbitrary which one to use).
SELECT min(id)
FROM example
GROUP BY first_name, last_name
Using min on ID will return:
ID FIRST_NAME LAST_NAME
1 Brian Smith
3 George Smith
If you use max you would get
ID FIRST_NAME LAST_NAME
25 Brian Smith
3 George Smith
I usually use this technique to delete the duplicates, not update them:
DELETE FROM example
WHERE ID NOT IN (SELECT MAX (ID)
FROM example
GROUP BY first_name, last_name)