[Previous essay-title for question]
Oracle SQL: update parent table column if all child table rows have specific value in a column. Update RANK of only those students who have 100 marks in all the subjects. If student has less than 100 marks in any subject, his RANK should not be updated.
I have a scenario where I have a parent table and a child table. The child table has a foreign key to parent table. I need to update parent table's status column when a column in child table rows have specific values. There are more than one child records for each parent, in some cases none. Is it possible to achieve this with Oracle SQL, without using PL/SQL. Is that possible, can some one explain how? In some case I have to update parent table row's column based on two columns of child table records.
My exact problem is like : I have two tables STUDENTS, MARKS. MARKS has a FK to STUDENTS named STUDENT_ID.MARKS has number of rows for a STUDENT record, depending on different subjects (MARKS has a FK to SUBJECTS), and has a column named MARKS_OBTAINED. I have to check that if MARKS_OBTAINED for one student for every subject (i.e. all his records in MARKS) have value 100, then update STUDENT table's column RANK to a value 'Merit'. This query:
update STUDENT
set RANK = 'Merit'
where exists ( select *
from MARKS
where MARKS.STUDENT_ID = STUDENT.ID
and MARKS.MARKS_OBTAINED = 100)
and not exists ( select *
from MARKS
where MARKS.STUDENT_ID = STUDENT.ID
and MARKS.MARKS_OBTAINED != 100)
updates all those student who have 100 marks in any subject. It does not exclude records which have non 100 marks. Because it passes rows for a STUDENT in MARKS where one record in MARKS has 100 MARKS_OBTAINED but other records have less than 100 marks, but since STUDENT obtained 100 marks in one subject, its RANK will also get updated. The requirement is that if any STUDENT records has a MARKS record with non 100 value in MARKS_OBTAINED column this STUDENT record should get excluded from the query.
Total rewrite
This is a complete rewrite to fit my example to the OQ's revised question. Unfortunately Manish has not actually run my original solution otherwise they would realise the following assertion is wrong:
Your solution returns all those
student who have 100 marks in any
subject. It does not exclude records
which have non 100 marks.
Here are six students and their marks.
SQL> select * from student
2 /
ID RANK
---------- ----------
1 normal
2 normal
3 normal
4 normal
5 normal
6 normal
6 rows selected.
SQL> select * from marks
2 /
COURSE_ID STUDENT_ID MARK
---------- ---------- ----------
1 1 100
2 1 100
1 2 100
2 2 99
1 4 100
2 5 99
1 6 56
2 6 99
8 rows selected.
SQL>
Student #1 has two courses with marks of 100. Student #4 has just the one course but with with a mark of 100. Student #2 has a mark of 100 in one course but only 99 in the other course they have taken. None of the other students scored 100 in any course. Which students will be awarded a 'merit?
SQL> update student s
2 set s.rank = 'merit'
3 where exists ( select null
4 from marks m
5 where m.student_id = s.id
6 and m.mark = 100 )
7 and not exists ( select null
8 from marks m
9 where m.student_id = s.id
10 and m.mark != 100)
11 /
2 rows updated.
SQL>
SQL> select * from student
2 /
ID RANK
---------- ----------
1 merit
2 normal
3 normal
4 merit
5 normal
6 normal
6 rows selected.
SQL>
And lo! Only those students with 100 marks in all their courses have been updated. Never underestimate the power of an AND.
So the teaching is: an ounce of testing is worth sixteen tons of supposition.
Your question is a little too vague at the moment to really answer fully. What happens to a parent row if it has no children? What happens if some of the child rows have specific values but not all of them? In the two-column case, what combinations of number of children/values are needed (is is the same set of values for each column or unique ones? Is it an AND relationship or an OR relationship)? Etc...
Anyway, making the assumption that there needs to be at least one child row with a value in a given domain, this should be fairly straightforward:
update PARENT set STATUS = 'whatever'
where ID in (
select parent_id from CHILD
where value_col in ('your', 'specific', 'values', 'here')
);
This general pattern expands to the multi-column case easily (just add an extra AND or ORed condition to the inner where clause), and to the negative case too (change where ID in to where ID not in).
If performance of this update is an issue you may want to look at triggers - at the price of slightly slower inserts on the child tables, you can keep your parent table up-to-date on an ongoing basis without having to run this update statement periodically. This works quite nicely because the logic of inspecting each child row is essentially distributed across each individual insert or update on the child table. Of course, if those child modifications are performance-critical, or if the child changes many times in between the points where you need to update the parent, then this wouldn't work very well.
What about:
UPDATE ParentTable
SET StatusColumn = 78
WHERE PK_Column IN
(SELECT DISTINCT FK_Column
FROM ChildTable AS C1
WHERE (SELECT COUNT(*) FROM ChildTable C2
WHERE C1.FK_Column = C2.FK_Column) =
(SELECT COUNT(*) FROM ChildTable C3
WHERE C1.FK_Column = C3.FK_Column
AND C3.OtherColumn = 23)
)
I strongly suspect there are neater ways to do it, but...the correlated sub-queries count the number of rows in the child table for a particular parent and the number of rows in the child table for the same parent where some filter condition matches a particular value. Those FK_Column values are returned to the main UPDATE statement, giving a list of primary key values for which the status should be updated.
This code enforces the stringent condition 'all matching rows in the child table satisfy the specific condition'. If your condition is simpler, your sub-query can be correspondingly simpler.
Related
For my project, I have 2 tables. Initially I inner joined both tables (table 1 and 2) via an inner join. However, I wanted an outcome as seen in table 4 where the repeated value from table 1 is left blank instead.
For table 2, the number of rows will always vary. There will always only be 1 department ID attached to numerous function IDs. Is there a query then where regardless of the number of function IDs, the department ID will only appear as the first row as seen in table 4?
(I think to many, this might seem weird and frankly not clean data, but for mail merges within word, it is easier to field code when the data is presented this way to refrain sections from 'reprinting itself'.)
Current Code:
SELECT Table1.*, Table2.* FROM
INNER JOIN Table 2 ON Table1.DepartmentID = Table2.DepartmentID
Table 1:
Department ID
Department
1
XYZ
Table 2:
Department ID
Function ID
Function
1
1
ABC
1
2
DEF
Table 3 (inner joined):
Department ID
Department
FunctionID
Function
1
XYZ
1
ABC
1
XYZ
2
DEF
Table 4 (desired):
Department ID
Department
FunctionID
Function
1
XYZ
1
ABC
2
DEF
Problem
I have a situation in which I have two tables in which I would like the entries from table 2 (lets call it table_2) to be matched up with the entries in table 1 (table_1) such that there are no duplicates rows of table_2 used in the match up.
Discussion
Specifically, in this case there are datetime stamps in each table (field is utcdatetime). For each row in table_1, I want to find the row in table_2 in which has the closed utcdatetime to the table 1 utcdatetime such that the table2.utcdatetime is older than the table_1 utcdatetime and within 30 minutes of the table 1 utcdatetime. Here is the catch, I do not want any repeats. If a row in table 2 gets gobbled up in a match on an earlier row in table 1, then I do not want it considered for a match later.
This has currently been implemented in a Python routine, but it is slow to iterate over all of the rows in table 1 as it is large. I thought I was there with a single SQL statement, but I found that my current SQL results in duplicate table 2 rows in the output data.
I would recommend using a nested select to get whatever results you're looking for.
For instance:
select *
from person p
where p.name_first = 'SCCJS'
and not exists (select 'x' from person p2 where p2.person_id != p.person_id
and p.name_first = 'SCCJS' and p.name_last = 'SC')
I have an SQL Server 2012 table with ID, First Name and Last name. The ID is unique per person but due to an error in the historical feed, different people were assigned the same id.
------------------------------
ID FirstName LastName
------------------------------
1 ABC M
1 ABC M
1 ABC M
1 ABC N
2 BCD S
3 CDE T
4 DEF T
4 DEG T
In this case, the people with ID’s 1 are different (their last name is clearly different) but they have the same ID. How do I query and get the result? The table in this case has millions of rows. If it was a smaller table, I would probably have queried all ID’s with a count > 1 and filtered them in an excel.
What I am trying to do is, get a list of all such ID's which have been assigned to two different users.
Any ideas or help would be very appreciated.
Edit: I dont think I framed the question very well.
There are two ID's which are present multiple time. 1 and 4. The rows with id 4 are identical. I dont want this in my result. The rows with ID 1, although the first name is same, the last name is different for 1 row. I want only those ID's whose ID is same but one of the first or last names is different.
I tried loading ID's which have multiple occurrences into a temp table and tried to compare it against the parent table albeit unsuccessfully. Any other ideas that I can try and implement?
SELECT
ID
FROM
<<Table>>
GROUP BY
ID
HAVING
COUNT(*) > 1;
SELECT *
FROM myTable
WHERE ID IN (
SELECT ID
FROM myTable
GROUP BY ID
HAVING MAX(LastName) <> MIN(LastName) OR MAX(FirstName) <> MIN(FirstName)
)
ORDER BY ID, LASTNAME
for example :
I have a table with student ID and student grades
-----------------------
ID | grades
-----------------------
1 | 80
2 | 28
-----------------------
I want to get 0 when I query about ID = 3
can I do that ?
like select grades from student where id = 3 .
I want to get 0 because ID is not in the table
Run a select command with the reserved function called count:
select count(*) from STUDENT.GRADES where ID=3
It should be just like that.
Maybe this will do what you want:
SELECT ID, MAX(Grades)
FROM (SELECT ID, Grade FROM Students WHERE ID = 3
UNION
VALUES (3, 0) -- Not certain of syntax here
)
GROUP BY ID
The basic idea is that students present in the table will have two rows and the MAX will pick their proper grade (assuming that there are no circumstances where the grade is coded as a negative value). Students that are not represented will have just the one row with a grade of 0. The repeated 3 is the ID of the student being sought.
Have fun chasing down the full syntax. I started at Queries in the DB2 9.7 Information Centre, but ran out of patience before I got a good answer — and I don't have DB2 to experiment on. You might need to write SELECT ID, Grades FROM VALUES (3, 0), or there might be some other magical incantation that does the job. You could probably use SELECT 3 AS ID, 0 AS Grades FROM SYSIBM.SYSTABLES WHERE TABID = 1, but that's a clumsy expression.
I've kept with the column name Grades (plural) even though it looks like it contains one grade. It is depressing how often people ask questions about anonymous tables.
I have a single table of activities, some labelled 'Assessment' (type_id of 50) and some 'Counselling' (type_id of 9) with dates of the activities. I need to compare these dates to find how long people wait for counselling after assessment. The table contains rows for many people, and that is the primary key of 'id'. My problem is how to produce a result row with both the assessment details and the counselling details for the same person, so that I can compare the dates. I've tried joining the table to itself, and tried nested subqueries, I just can't fathom it. I'm using Access 2010 btw.
Please forgive my stupidity, but here's an example of joining the table to itself that doesn't work, producing nothing (not surprising):
Table looks like:
ID TYPE_ID ACTIVITY_DATE_TIME
----------------------------------
1 9 20130411
1 v 50 v 20130511
2 9 20130511
3 9 20130511
In the above the last two rows have only had assessment so I want to ignore them, and just work on the situation where there's both assessment and counselling 'type-id'
SELECT
civicrm_activity.id, civicrm_activity.type_id,
civicrm_activity.activity_date_time,
civicrm_activity_1.type_id,
civicrm_activity_1.activity_date_time
FROM
civicrm_activity INNER JOIN civicrm_activity AS civicrm_activity_1
ON civicrm_activity.id = civicrm_activity_1.id
WHERE
civicrm_activity.type_id=9
AND civicrm_activity_1.type_id=50;
I'm actually wondering whether this is in fact not possible to do with SQL? I hope it is possible? Thank you for your patience!
Sounds to me like you only want to get the ID numbers where you have a TYPE_ID entry of both 9 and 50.
SELECT DISTINCT id FROM civicrm_activity WHERE type_id = '9' AND id IN (SELECT id FROM civicrm_activity WHERE type_id = '50');
This will give you a list of id's that has entries with both type_id 9 and 50. With that list you can now go and get the specifics.
Use this SQL for the time of type_id 9
SELECT activity_date_time FROM civicrm_activity WHERE id = 'id_from_last_sql' AND type_id = '9'
Use this SQL for the time of type_id 50
SELECT activity_date_time FROM civicrm_activity WHERE id = 'id_from_last_sql' AND type_id = '50'
Your query looks OK to me, too. The one problem might be that you use only one table alias. I don't know, but perhaps Access treats the table name "specially" such that, in effect, the WHERE clause says
WHERE
civicrm_activity.type_id=9
AND civicrm_activity.type_id=50;
That would certainly explain zero rows returned!
To fix that, use an alias for each table. I suggest shorter ones,
SELECT A.id, A.type_id, A.activity_date_time,
B.type_id, B.activity_date_time
FROM civicrm_activity as A
JOIN civicrm_activity as B
ON A.id = B.id
WHERE A.type_id=9
AND B.type_id=50;