I have the above mentioned tables in my database. I first receive a COURSE variable from my previous PHP page. I need to print the list of student names along with their student_Ids who haven't taken the course. For the tables above, if the variable I receive is A, then I need to print Jake along with his student_id. As Jake's student id 3, is not associaetd with Course A.
I tried following query, which doesn't seem to work and I'm unsure where I'm wrong
SELECT DISTINCT T1.name, T1.student_id
FROM Table 1 T1, Table 2 T2
WHERE T1.student_id = T2.student_id AND
T2.COURSE != :variable
ORDER BY T1.name ASC,
T1.student_id ASC
variable : A
I appreciate that this must seem very old-fashioned, but then again, so am I...
SELECT DISTINCT x.*
FROM t1 x
LEFT
JOIN t2 y
ON y.student_id = x.student_id
AND y.course = 'a'
WHERE y.student_id IS NULL;
There are lots of options. For instance, you could use a subquery:
SELECT name, student_id FROM t1 WHERE student_id NOT IN (SELECT student_id FROM t2 WHERE course='A')
You can use NOT EXISTS to find a list of students who have not taken the course:
SELECT * FROM T1
WHERE NOT EXISTS (
SELECT * FROM T2
WHERE T1.StudentId = T2.StudentId
AND T2.Course = :variable
)
ORDER BY name ASC, student_id
Related
I am trying to merge the rows based on condition in mysql.
I have table as shown below :
Looking merge the row 1 into row 2 (where the attendance count is larger)
and need to shown the result as :
I was trying to divide the dataset into 2 parts using the below query
select
a.student_id,a.school_id,a.name,a.grant,a.classification,a.original_classification,,a.consent_type
from (
select * from school_temp where original_classification='all' and availability='implicit')a
join(select * from school_temp where original_classification!='all' and availability!='implicit')b
on a.student_id = b.student_id and a.school_id=b.school_id and a.name=b.name
But unable to merge the rows and get total attendance count .
Please help me ,i am badly stuck in this
Split this into two queries that you combine with UNION.
The first joins the implicit row with the row with the highest attendance among the explicit rows for each student. See Retrieving the last record in each group - MySQL for how that works. Use SUM(attendance_count) to combine the attendances.
The second query in the UNION gets all the rows that don't have the highest attendance.
WITH explicit as (
SELECT *
FROM school_temp
WHERE original_classification!='all' and availability!='implicit'
)
SELECT a.student_id, a.school_id, a.name, SUM(attendance_count) AS attendance_count,
b.grant, b.classification, b.original_classification, b.consent_type
FROM school_temp AS a
JOIN (
SELECT t1.*
FROM explicit AS t1
JOIN (
SELECT student_id, school_id, name, MAX(attendance_count) AS max_attendance
FROM explicit AS t2
GROUP BY student_id, school_id, name
) AS t2 ON t1.student_id = t2.student_id AND t1.school_id = t2.school_id AND t1.name = t2.name AND t1.attendance_count = t2.max_attendance
) AS b ON a.student_id = b.student_id and a.school_id=b.school_id and a.name=b.name
WHERE a.original_classication = 'all' AND a.availability = 'implicit'
UNION ALL
SELECT t1.*
FROM explicit AS t1
JOIN (
SELECT student_id, school_id, name, MAX(attendance_count) AS max_attendance
FROM explicit AS t2
GROUP BY student_id, school_id, name
) AS t2 ON t1.student_id = t2.student_id AND t1.school_id = t2.school_id AND t1.name = t2.name AND t1.attendance_count < t2.max_attendance
I've used a CTE to give a name to the subquery that gets all the explicit rows. If you're using MySQL 5.x, you'll need to replace explicit with that subquery throughout the query. Or you could define it as a view.
Here is what I currently have which returns 3 columns for patient_id, group_concat_1, and group_concat_2:
SELECT patient_id,
(SELECT GROUP_CONCAT(column1) FROM
table1 where patient_id = patient.id
) group_concat_1,
(SELECT GROUP_CONCAT(column1) FROM
table2 where patient_id = patient.id
) group_concat_2
FROM patient
However, I need to return a single column with group_concat_1 and group_concat_2 combined, so I tried this:
SELECT patient_id,
SELECT CONCAT(group_concat_1, group_concat_2) FROM (
(SELECT GROUP_CONCAT(column1) FROM
table1 where patient_id = patient.id
) group_concat_1,
(SELECT GROUP_CONCAT(column1) FROM
table2 where patient_id = patient.id
) group_concat_2
)
FROM patient
But his clearly doesn't work since now it can't find patient.id in the inner subquery. Any advice? Thanks!
You can concatenate directly the 2 columns:
SELECT p.patient_id,
CONCAT(
(SELECT GROUP_CONCAT(column1) FROM table1 where patient_id = p.patient.id),
(SELECT GROUP_CONCAT(column1) FROM table2 where patient_id = p.patient.id)
)
FROM patient p
I'm pretty sure you want concat_ws() for this purpose:
SELECT patient_id,
CONCAT_WS(','
(SELECT GROUP_CONCAT(t1.column1) FROM table1 t1 where t1.patient_id = p.id
),
(SELECT GROUP_CONCAT(t2.column1) FROM table2 t2 where t2.patient_id = p.id
)
) as combined
FROM patient p;
There are two reasons:
You can distinguish between the last element from table1 and the first from `table2.
If one of the tables has no matching values, this returns the results from the other.
Also note that I added table aliases and qualified column names. This is quite important when working with queries that have multiple table references -- it helps prevent some very hard to debug errors.
I should add that your original query would run in most databases. MySQL and Oracle happen to be two that don't understand nested correlation clauses.
I don't know if my title is understandable or not, may be someone can help edit my title?
All I want to do is, for example:
I have a table like this
Engineering appears 5 times with different article_category_abbr, and I want to select only one row with the biggest value of num.
Here, it will be Engineering-ENG-192, and Geriatrics&Gerontology will be Geriatrics&Gerontology-CLM-26
But I don't know how to do it on the whole table using mysql
Join your table to a subquery which finds the greatest num value for each sc group.
SELECT t1.*
FROM yourTable t1
INNER JOIN
(
SELECT sc, MAX(num) AS max_num
FROM yourTable
GROUP BY sc
) t2
ON t1.sc = t2.sc AND
t1.num = t2.max_num;
You can have a subquery that gets the largest value for each sc and the resulting rows will then be joined with the table itself based from two columns - sc and num.
SELECT a.*
FROM tableName a
INNER JOIN
(
SELECT sc, MAX(num) AS Num
FROM tableName
GROUP BY sc
) b ON a.sc = b.sc
AND a.num = b.num
Here's a Demo
USE MAX function and GROUP BY like this. Here is more information.
SELECT myID, classTitle, subField, MAX(score) FROM myTable GROUP BY myID, classTitle, subField
Is there a way to tell MySQL that while making something like this
SELECT id, MAX(seq) FROM t1 GROUP BY ident;
I can also get the id value? I know I shouldn't be using id if it's not in a group by but I feel like its strange to make a multi pass to get the row ids with the maximum seq field when it already passed it. So what is the most effective way to do this? id is the primary key
SELECT a.*
FROM tableName
INNER JOIN
(
SELECT ident, MAX(seq) seq
FROM tableName
GROUP BY ident
) b ON a.ident = b.ident AND
a.seq = b.seq
Mabye:
SELECT MAX(a.seq), (SELECT id FROM t1 as b where b.ident=a.ident AND MAX(a.seq) = b.seq LIMIT 1) as id FROM t1 AS a GROUP BY a.ident;
Fiddle
Try using self-join:
SELECT t1.* FROM MyTable t1
JOIN
(SELECT ident, MAX(seq) AS MAX_Seq
FROM MyTable
GROUP BY ident
) t2
ON t1.seq = t2.MAX_Seq
AND t1.ident = t2.ident
See this sample SQLFiddle
What is seq exactly ?
I guess you can also order your results ?
SELECT id FROM t1 GROUP BY ident ORDER BY seq DESC
Regarding to the others answer, seq is in another table ?
i have table as
id----name----roll-----class
1----ram-------1-----2
2----shyam-----2-----3
3----ram-------1-----3
4----shyam-----2-----3
5----ram-------1-----2
6----hari------1-----5
i need to find the the duplicate row only that have common name, roll, class. so the expected result for me is.
id----name----roll-----class
1----ram-------1-------2
2----shyam-----2-------3
4----shyam-----2-------3
5----ram-------1-------2
i tried to get from the query below but here only one field is supported. i need all three field common. Please do help me in this. thanks
SELECT *
FROM table
WHERE tablefield IN (
SELECT tablefield
FROM table
GROUP BY tablefield
HAVING (COUNT(tablefield ) > 1)
)
You can use count() over().
select id, name, roll, class
from (select id, name, roll, class,
count(*) over(partition by name, roll, class) as c
from YourTable) as T
where c > 1
order by id
https://data.stackexchange.com/stackoverflow/query/63720/duplicates
this will retun only the duplicate entry one time:
select t.id, t.name, t.roll, t.class
from table t
inner join table t1
on t.id<t1.id
and t.name=t1.name
and t.roll = t1.roll
and t.class=t1.class
this will return what you require:
select distinct t.id, t.name, t.roll, t.class
from table t
inner join table t1
on t.name=t1.name
and t.roll = t1.roll
and t.class=t1.class
I'd suggest something like this
SELECT A.* FROM
Table A LEFT OUTER JOIN Table B
ON A.Id <> B.Id AND A.Name = B.Name AND A.Roll = B.Roll AND A.Class = B.Class
WHERE B.Id IS NOT NULL
Something like that should work (I did not test though):
select a1.*
from table a1, a2
where (a1.id != a2.id)
and (a1.name == a2.name)
and (a1.roll== a2.roll)
and (a1.class== a2.class);
It seems there are several proprosals here. If it is a query that you'll use in your code, beware of the cost of the queries. Try an 'explain' with your database.