I would like to show all classes and grades of only those students who have at least one "F" grade.
Here is the source table:
ID | Students | Class | Grade
1 | Addams, W | History | A
2 | Addams, W | Biology | A
3 | Addams, W | French | B
4 | Jetson, E | Spanish | B
5 | Jetson, E | Geometry | B
6 | Jetson, E | Biology | F
7 | Rubble, B | English | F
8 | Rubble, B | Geometry | B
9 | Rubble, B | Biology | B
10 | Flintstone, P | Music | A
11 | Flintstone, P | Spanish | B
Here is a report, grouped by Students:
Addams, W
---------------French B
---------------Biology A
---------------History A
Flintstone, P
---------------Spanish B
---------------Music A
Jetson, E
---------------Biology F
---------------Geometry B
---------------Spanish B
Rubble, B
---------------Biology B
---------------Geometry B
---------------English F
Again, I would like to show all classes and grades of only those students who have at least one "F" grade, as seen below:
Jetson, E
---------------Biology F
---------------Geometry B
---------------Spanish B
Rubble, B
---------------Biology B
---------------Geometry B
---------------English F
Any assistance would be much appreciated.
Create a query with your table as the source. Drop in the Students field in the first column and put the following formula in the second column: IIf([Grade]=”F”,1,0), then save the query. (by default Access will name this column “Expr1”, but you change it to whatever you like)
Create a 2nd query using query 1 as the source, drop in the 2 columns from query 1, group on, sum the column with the formula, and in this column add a criteria of >=1, and save. You now have a table with only the students who have at least 1 “F”. (you group on by placing cursor in the grid section of the query at the bottom, right-clicking and selecting "Totals" from the prompt box)
Create a 3rd query tying the 2nd query to your original source table by connecting the Students field with a 1 to 1 match (i.e. join type 1).
You can query your table using a subquery to query on the same table for any instances having a F grade:
SELECT a.ID, a.Students, a.Class, a.Grade
FROM yourtable AS a
WHERE EXISTS
(
SELECT '1'
FROM yourtable AS b
WHERE a.Students = b.Students
AND b.Grade = 'F'
);
Next, base your report on above query.
OP here: Both answers worked; thanks again. Here is the code for the second answer:
Query 1
SELECT Students2.Students, IIf([Grade]="F",1,0) AS F_grade
FROM Students2;
Query 2
SELECT Query1.Students, Sum(Query1.F_grade) AS SumOfF_grade
FROM Query1
GROUP BY Query1.Students
HAVING (((Sum(Query1.F_grade))>=1));
Query 3
SELECT Students2.Students, Students2.Class, Students2.Grade
FROM Students2 INNER JOIN Query2 ON Students2.Students = Query2.Students;
Related
I have two tables, one is a table of employee names, 176 records. The other is a table (with duplicates) of employee names (same format) and their locations (7943 rows).
From this answer i deduced i needed a left join to give me the rows from Table A only.
I was hoping the below would give me the original 176 rows back from Table A, each column with a value for location from Table B, else blank if not available, however it gives me 7601 rows which i cannot for the life of me understand:
SELECT e.[UniqueName], l.[location]
FROM [Employees] as e
left join Locations as l
on e.[UniqueName] = l.[UniqueName]
Even using a group by (which I'm not sure why this would be necessary given that I am asking only for whats in Table A) gives 172 rows even though each name in the Employees table is unique!
The table Locations contains more than 1 locations for each employee and this is why you get so many rows in the results.
If you want just 1 location and it does not matter which 1 then add aggregation to your query:
SELECT e.[UniqueName], MAX(l.[location]) AS location
FROM [Employees] as e
LEFT JOIN Locations as l
ON e.[UniqueName] = l.[UniqueName]
GROUP BY e.[UniqueName]
You can use MIN() instead of MAX().
I was hoping the below would give me the original 176 rows back from
Table A, each column with a value for location from Table B, else
blank if not available, however it gives me 7601 rows which I cannot
for the life of me understand...
Whilst a left join will always return all records from the dataset on the lefthand side of the join, the number of records returned by the query will depend upon the number of possible pairings between the two datasets, which (for a left join) will always be greater than or equal to the number of records in the dataset to the left of the join.
For your example, consider the following two datasets:
Employees
+------------+
| UniqueName |
+------------+
| Alice |
| Bob |
| Charlie |
+------------+
Locations
+------------+----------+
| UniqueName | Location |
+------------+----------+
| Alice | London |
| Bob | Berlin |
| Bob | New York |
| Bob | Paris |
+------------+----------+
Evaluating the query:
select
e.[uniquename], l.[location]
from
[employees] as e left join locations as l
on e.[uniquename] = l.[uniquename]
Will cause the records to be paired up in the following manner:
And will therefore return the result:
+------------+----------+
| uniquename | location |
+------------+----------+
| Alice | London |
| Bob | Berlin |
| Bob | New York |
| Bob | Paris |
| Charlie | |
+------------+----------+
You can use a correlated subquery:
SELECT e.[UniqueName],
(SELECT TOP 1 l.[location]
FROM locations as l
WHERE e.[UniqueName] = l.[UniqueName]
) as location
FROM [Employees] as e;
Note: There is no ORDER BY so this returns an arbitrary location.
If location can be duplicated for a given UniqueName, you will get an error. To solve that, you can use an aggregation functions:
SELECT e.[UniqueName],
(SELECT MAX(l.[location])
FROM locations as l
WHERE e.[UniqueName] = l.[UniqueName]
) as location
FROM [Employees] as e;
I Have a query that finds a table, here's an example one.
Name |Age |Hair |Happy | Sad |
Jon | 15 | Black |NULL | NULL|
Kyle | 18 |Blonde |YES |NULL |
Brad | 17 | Blue |NULL |YES |
Name and age come from one table in a database, hair color comes from a second which is joined, and happy and sad come from a third table.My goal would be to make the first line of the chart like this:
Name |Age |Hair |Happy |Sad |
Jon | 15 |Black |Yes |Yes |
Basically I want to get rid of the rows under the first and get the non NULL data joined to the right. The problem is that there is no column where the Yes values are on the Jon row, so I have no idea how to get them there. Any suggestions?
PS. With the data I am using I can't just put a 'YES' in the 'Jon' row and call it a day, I would need to find the specific value from the lower rows and somehow get that value in the boxes that are NULL.
Do you just want COALESCE()?
COALESCE(Happy, 'Yes') as happy
COALESCE() replaces a NULL value with another value.
If you want to join on a NULL value work with nested selects. The inner select gets an Id for NULLs, the outer select joins
select COALESCE(x.Happy, yn_table.description) as happy, ...
from
(select
t1.Happy,
CASE WHEN t1.Happy is null THEN 1 END as happy_id
from t1 ...) x
left join yn_table
on x.xhappy_id = yn_table.id
If you apply an ORDER BY to the query, you can then select the first row relative to this order with WHERE rownum = 1. If you don't apply an ORDER BY, then the order is random.
After reading your new comment...
the sense is that in my real data the yes under the other names will be a number of a piece of equipment. I want the numbers of the equipment in one row instead of having like 8 rows with only 4 ' yes' values and the rest null.
... I come to the conclusion that this a XY problem.
You are asking about a detail you think will solve your problem, instead of explaining the problem and asking how to solve it.
If you want to store several pieces of equipment per person, you need three tables.
You need a Person table, an Article table and a junction table relating articles to persons to equip them. Let's call this table Equipment.
Person
------
PersonId (Primary Key)
Name
optional attributes like age, hair color
Article
-------
ArticleId (Primary Key)
Description
optional attributes like weight, color etc.
Equipment
---------
PersonId (Primary Key, Foreign Key to table Person)
ArticleId (Primary Key, Foreign Key to table Article)
Quantity (optional, if each person can have only one of each article, we don't need this)
Let's say we have
Person: PersonId | Name
1 | Jon
2 | Kyle
3 | Brad
Article: ArticleId | Description
1 | Hat
2 | Bottle
3 | Bag
4 | Camera
5 | Shoes
Equipment: PersonId | ArticleId | Quantity
1 | 1 | 1
1 | 4 | 1
1 | 5 | 1
2 | 3 | 2
2 | 4 | 1
Now Jon has a hat, a camera and shoes. Kyle has 2 bags and one camera. Brad has nothing.
You can query the persons and their equipment like this
SELECT
p.PersonId, p.Name, a.ArticleId, a.Description AS Equipment, e.Quantity
FROM
Person p
LEFT JOIN Equipment e
ON p.PersonId = e.PersonId
LEFT JOIN Article a
ON e.ArticleId = a.ArticleId
ORDER BY p.Name, a.Description
The result will be
PersonId | Name | ArticleId | Equipment | Quantity
---------+------+-----------+-----------+---------
3 | Brad | NULL | NULL | NULL
1 | Jon | 4 | Camera | 1
1 | Jon | 1 | Hat | 1
1 | Jon | 5 | Shoes | 1
2 | Kyle | 3 | Bag | 2
2 | Kyle | 4 | Camera | 1
See example: http://sqlfiddle.com/#!4/7e05d/2/0
Since you tagged the question with the oracle tag, you could just use NVL(), which allows you to specify a value that would replace a NULL value in the column you select from.
Assuming that you want the 1st row because it contains the smallest age:
- wrap your query inside a CTE
- in another CTE get the 1st row of the query
- in another CTE get the max values of Happy and Sad of your query (for your sample data they both are 'YES')
- cross join the last 2 CTEs.
with
cte as (
<your query here>
),
firstrow as (
select name, age, hair from cte
order by age
fetch first row only
),
maxs as (
select max(happy) happy, max(sad) sad
from cte
)
select f.*, m.*
from firstrow f cross join maxs m
You can try this:
SELECT A.Name,
A.Age,
B.Hair,
C.Happy,
C.Sad
FROM A
INNER JOIN B
ON A.Name = B.Name
INNER JOIN C
ON A.Name = B.Name
(Assuming that Name is the key columns in the 3 tables)
I'm trying to better understand relational algebra and am having trouble solving the following type of question:
Suppose there is a column A (Department), a column B (Employees) and a column C (Managers). How can I find all of the departments who only have one manager for all of their employees? An example is provided below:
Department | Employees | Managers
-------------+-------------+----------
A | John | Bob
A | Sue | Sam
B | Jim | Don
B | Alex | Don
C | Jason | Xie
C | Greg | Xie
In this table, the result I should get are all tuples containing departments B and C because all of their employees are managed by the same person (Don and Xie respectively). Department A however, would not be returned because it's employees have multiple managers.
Any help or pointers would be appreciated.
Such problems usually call for a self-join.
Joining the relation onto itself on Department, then filtering out the tuples where the Managers are equal would yield us all the unwanted tuples, which we can just subtract from the original relations.
Here's how I'd do it:
First we make a copy of table T, and call it T2, then take a cross product of T and T2. From the result we select all the rows where T1.Manager /= T2.Manager but T1.Department=T2.Department, yielding us these tuples:
T1.Department | T1.Employees| T1.Managers | T2.Managers | T2.Employees | T2.Department
--------------+-------------+-------------+-------------+--------------+--------------
A | John | Bob | Sam | Sue | A
A | Sue | Sam | Bob | John | A
Departments A and B aren't present because their T1.Manager always equals T2.Manager.
Then we just subtract this result the original set to get the answer.
If your RDBMS supports common table expressions:
with C as (
select department, manager, count(*) as cnt
from A
group by department, manager
),
B as (
select department, count(*) as cnt
from A group by department
)
select A.*
from A
join C on A.department = C.department
join B on A.department = B.department
where B.cnt = C.cnt;
I am trying to select the max value from one column, while grouping by another non-unique id column which has multiple duplicate values. The original database looks something like:
mukey | comppct_r | name | type
65789 | 20 | a | 7n
65789 | 15 | b | 8m
65789 | 1 | c | 1o
65790 | 10 | a | 7n
65790 | 26 | b | 8m
65790 | 5 | c | 1o
...
This works just fine using:
SELECT c.mukey, Max(c.comppct_r) AS ComponentPercent
FROM c
GROUP BY c.mukey;
Which returns a table like:
mukey | ComponentPercent
65789 | 20
65790 | 26
65791 | 50
65792 | 90
I want to be able to add other columns in without affecting the GROUP BY function, to include columns like name and type into the output table like:
mukey | comppct_r | name | type
65789 | 20 | a | 7n
65790 | 26 | b | 8m
65791 | 50 | c | 7n
65792 | 90 | d | 7n
but it always outputs an error saying I need to use an aggregate function with select statement. How should I go about doing this?
You have yourself a greatest-n-per-group problem. This is one of the possible solutions:
select c.mukey, c.comppct_r, c.name, c.type
from c yt
inner join(
select c.mukey, max(c.comppct_r) comppct_r
from c
group by c.mukey
) ss on c.mukey = ss.mukey and c.comppct_r= ss.comppct_r
Another possible approach, same output:
select c1.*
from c c1
left outer join c c2
on (c1.mukey = c2.mukey and c1.comppct_r < c2.comppct_r)
where c2.mukey is null;
There's a comprehensive and explanatory answer on the topic here: SQL Select only rows with Max Value on a Column
Any non-aggregate column should be there in Group By clause .. why??
t1
x1 y1 z1
1 2 5
2 2 7
Now you are trying to write a query like:
select x1,y1,max(z1) from t1 group by y1;
Now this query will result only one row, but what should be the value of x1?? This is basically an undefined behaviour. To overcome this, SQL will error out this query.
Now, coming to the point, you can either chose aggregate function for x1 or you can add x1 to group by. Note that this all depends on your requirement.
If you want all rows with aggregation on z1 grouping by y1, you may use SubQ approach.
Select x1,y1,(select max(z1) from t1 where tt.y1=y1 group by y1)
from t1 tt;
This will produce a result like:
t1
x1 y1 max(z1)
1 2 7
2 2 7
Try using a virtual table as follows:
SELECT vt.*,c.name FROM(
SELECT c.mukey, Max(c.comppct_r) AS ComponentPercent
FROM c
GROUP BY c.muke;
) as VT, c
WHERE VT.mukey = c.mukey
You can't just add additional columns without adding them to the GROUP BY or applying an aggregate function. The reason for that is, that the values of a column can be different inside one group. For example, you could have two rows:
mukey | comppct_r | name | type
65789 | 20 | a | 7n
65789 | 20 | b | 9f
How should the aggregated group look like for the columns name and type?
If name and type is always the same inside a group, just add it to the GROUP BY clause:
SELECT c.mukey, Max(c.comppct_r) AS ComponentPercent
FROM c
GROUP BY c.muke, c.name, c.type;
Use a 'Having' clause
SELECT *
FROM c
GROUP BY c.mukey
HAVING c.comppct_r = Max(c.comppct_r);
I'm trying to use a join on three tables query I found in another post (post #5 here). When I try to use this in the SQL tab of one of my tables in phpMyAdmin, it gives me an error:
#1066 - Not unique table/alias: 'm'
The exact query I'm trying to use is:
select r.*,m.SkuAbbr, v.VoucherNbr from arrc_RedeemActivity r, arrc_Merchant m, arrc_Voucher v
LEFT OUTER JOIN arrc_Merchant m ON (r.MerchantID = m.MerchantID)
LEFT OUTER JOIN arrc_Voucher v ON (r.VoucherID = v.VoucherID)
I'm not entirely certain it will do what I need it to do or that I'm using the right kind of join (my grasp of SQL is pretty limited at this point), but I was hoping to at least see what it produced.
(What I'm trying to do, if anyone cares to assist, is get all columns from arrc_RedeemActivity, plus SkuAbbr from arrc_Merchant where the merchant IDs match in those two tables, plus VoucherNbr from arrc_Voucher where VoucherIDs match in those two tables.)
Edited to add table samples
Table arrc_RedeemActivity
RedeemID | VoucherID | MerchantID | RedeemAmt
----------------------------------------------
1 | 2 | 3 | 25
2 | 6 | 5 | 50
Table arrc_Merchant
MerchantID | SkuAbbr
---------------------
3 | abc
5 | def
Table arrc_Voucher
VoucherID | VoucherNbr
-----------------------
2 | 12345
6 | 23456
So ideally, what I'd like to get back would be:
RedeemID | VoucherID | MerchantID | RedeemAmt | SkuAbbr | VoucherNbr
-----------------------------------------------------------------------
1 | 2 | 3 | 25 | abc | 12345
2 | 2 | 5 | 50 | def | 23456
The problem was you had duplicate table references - which would work, except for that this included table aliasing.
If you want to only see rows where there are supporting records in both tables, use:
SELECT r.*,
m.SkuAbbr,
v.VoucherNbr
FROM arrc_RedeemActivity r
JOIN arrc_Merchant m ON m.merchantid = r.merchantid
JOIN arrc_Voucher v ON v.voucherid = r.voucherid
This will show NULL for the m and v references that don't have a match based on the JOIN criteria:
SELECT r.*,
m.SkuAbbr,
v.VoucherNbr
FROM arrc_RedeemActivity r
LEFT JOIN arrc_Merchant m ON m.merchantid = r.merchantid
LEFT JOIN arrc_Voucher v ON v.voucherid = r.voucherid