I am selecting some columns from a table and adding some new columns (such as birthday and school address) with default values l
select
s.id,
s.address,
Birthday as null,
School_Address as 'Mumbai'
from student s;
But I am getting an error. Can someone tell me the right approach to assign these values.
You're doing it the wrong way round. First comes the value then the alias not the other way.
SELECT s.id,
s.address,
NULL birthday,
'Mumbai' school_address
FROM student s;
Related
Show how to define the view student grades (ID, GPA) giving the grade-point average of each student; recall that we used a relation grade_points (grade, points) to get the numeric points associated with a letter grade. Make sure your view definition correctly handles the case of null values for the grade attribute of the takes relation.
create view student_grades(ID, GPA) as
select ID, credit_ points / decode(credit sum, 0, NULL, credit_sum)
from ((select ID, sum(decode(grade, NULL, 0, credits)) as credit_sum,
sum(decode(grade, NULL, 0, credits*points)) as credit_points
from(takes natural join course) natural left outer join grade points group by ID)
union
select ID, NULL
from student
where ID not in (select ID from takes));
Can someone please correct this code?
I think you decode() and sum() parameters a mixed up !! Decode ask for 2 arguments
https://www.w3resource.com/mysql/encryption-and-compression-functions/decode().php
I have a Form that has a Field where the Lookup is set as a Combox Box Display Control, a Table / Query Row Source Type and a Query for the Row Source. I am wondering how to append non-bounded elements to this Combo Box.
Right now, the Combobox looks something like:
Mark
Chris
Mary
Charles
I would like for it to read as:
NONE
Mark
Chris
Mary
Charles
Of course, NONE is not an actual entry in my table. I would just like to append it for redundancy purposes.
My query for the Row Source is:
SELECT StudentId, StudentName FROM Student ORDER BY StudentId
I have tried just appending it like:
SELECT StudentId, StudentName, "NONE" FROM Student ORDER BY StudentId
But it completely skips the NONE part.
So, I am wondering if there's a way to append non-bounded elements to a Combobox that IS properly bound to a result set of a query.
You need union all :
SELECT s.*
FROM ((SELECT NULL AS StudentId, 'NONE' AS StudentName) UNION ALL
(SELECT StudentId, StudentName
FROM Student
)
) s;
You should use UNION in SQL query to join non-existing value
SELECT 0 as StudentId, 'NONE' as StudentName FROM Dual
UNION
SELECT StudentId, StudentName FROM Student
ORDER BY StudentId
Here Dual is table with one row
I'm working with a Pro*C query, but this question should be general SQL. My research has been a dead end, but I think I'm missing something.
Suppose my server has an array of students' names, {"Alice","Charlie","Bob"}. I query the Student_Ids table for the students' ID numbers:
SELECT id_no FROM student_ids
WHERE student_name IN ('Alice','Charlie','Bob');
To simplify server-side processing, I want to sort the result set in the same order as the students' names. In other words, the result set would be {alice_id_no, charlie_id_no, bob_id_no} regardless of the actual ordering of the table or the behavior of any particular vendor's implementation.
The only solution I can think of is:
. . .
ORDER BY
CASE WHEN student_name='Alice' THEN 0
WHEN student_name='Charlie' THEN 1
WHEN student_name='Bob' THEN 2 END;
but that seems extremely messy and cumbersome when trying to dynamically generate/run this query.
Is there a better way?
UPDATE I gave a terrible example by pre-sorting the students' names. I changed the names to be deliberately unsorted. In other words, I want to sort the names in a non-ASC or DESC-friendly way.
UPDATE II Oracle, but for knowledge's sake, I am looking for more general solutions as well.
The ORDER BY expression you've given for your sample data is equivalent to ORDER BY student_name. Is that what you intended?
If you want a custom ordering that is not alphabetical, I think you might have meant something like this:
ORDER BY
CASE
WHEN student_name = 'Alice' THEN 0
WHEN student_name = 'Charlie' THEN 1
WHEN student_name = 'Bob' THEN 2
END;
You can use a derived table as well, that holds the names as well as the ordering you want. This way you only have to put the names in a single time:
SELECT S.id_no
FROM
student_ids AS S
INNER JOIN (
SELECT Name = 'Alice', Seq = 0 FROM DUAL
UNION ALL SELECT 'Bob', 2 FROM DUAL
UNION ALL SELECT 'Charlie', 1 FROM DUAL
) AS N
ON S.student_name = N.Name
ORDER BY
N.Seq;
You could also put them into a temp table, but in Oracle that could be somewhat of a pain.
Can you do this?
order by student_name
To do a custom sort, you only need one case:
ORDER BY (CASE WHEN student_name = 'Alice' THEN 1
WHEN student_name = 'Bob' THEN 2
WHEN student_name = 'Charlie' THEN 3
ELSE 4
END)
why not this :
SELECT id_no FROM student_ids
WHERE student_name IN ('Alice','Bob','Charlie')
ORDER BY student_name
You can ORDER BY any columns, not necessary those in SELECT list or WHERE clause
SELECT id_no
FROM student_ids
WHERE student_name IN ('Alice','Bob','Charlie)
ORDER BY id_no;
Add a table to hold the sort priorities then you can use the sort_priorities in whatever query you want (and easily update the priorities):
CREATE TABLE student_name_sort_priorities (
student_name VARCHAR2(30) CONSTRAINT student_name_sort_priority__pk PRIMARY KEY,
sort_priority NUMBER(10) CONSTRAINT student_name_sort_priority__nn NOT NULL
CONSTRAINT student_name_sort_priority__u UNIQUE
);
(If you want two values to be equivalently sorted then don't include the UNIQUE constraint.)
INSERT INTO student_name_sort_priorities VALUES ( 'Alice', 0 );
INSERT INTO student_name_sort_priorities VALUES ( 'Charlie', 2 );
INSERT INTO student_name_sort_priorities VALUES ( 'Bob', 1 );
Then you can join the sort priority table with the student_ids table and use the extra column to perform ordering:
SELECT id_no
FROM student_ids s
LEFT OUTER JOIN
student_name_sort_priorities p
ON (s.student_name = p.student_name)
ORDER BY
sort_priority NULLS LAST;
I've used a LEFT OUTER JOIN so that if a name is not contained on the student_name_sort_priorities table then it does not restrict the rows returned from the query; NULLS LAST is used in the ordering for a similar reason - any student names that aren't in the sort priorities table will return a NULL sort priority and be placed at the end of the ordering. If you don't want this then just use INNER JOIN and remove the NULLS LAST.
How about using a 'table of varchar' type like the build-in below:
TYPE dbms_debug_vc2coll is table of varchar2(1000);
test:
SQL> select customer_id, cust_first_name, cust_last_name from customers where cust_first_name in
2 (select column_value from table(sys.dbms_debug_vc2coll('Frederic','Markus','Dieter')));
CUSTOMER_ID CUST_FIRST_NAME CUST_LAST_NAME
----------- -------------------- --------------------
154 Frederic Grodin
149 Markus Rampling
152 Dieter Matthau
That seems to force the order, but that might just be bad luck. I'm not really a sql expert.
The execution plan for this uses 'collection iterator' instead of a big 'or' in the typical:
select customer_id, cust_first_name, cust_last_name from customers where cust_first_name in ('Frederic','Markus','Dieter');
hth, Hein.
I have one table with gender as one of the columns.
In gender column only M or F are allowed.
Now i want to sort the table so that while displaying the table in gender field M and F will come alternetivly.
I have Tried....
I have tried to create one(new) table with the same structure as my existing table.
Now using high leval insert i want to insert M to odd rows and F to even rows.
After that i want to join those two statements using union operator.
I am able to insert to ( new ) the table only male or female but not to the even or odd rows...
Can any body help me regarding this....
Thanks in Advance....
Don't consider a table to be "sorted". The SQL server may return the rows in any order depending on execution plan, index, joins etc. If you want a strict order you need to have an ordered column, like an identity column. Usually it is better to apply the desired sorting when selecting data.
However the interleaving of M and F is a little bit tricky, you need to use the ROW_NUMBER function.
Valid SQL Server code:
CREATE TABLE #GenderTable(
[Name] [nchar](10) NOT NULL,
[Gender] [char](1) NOT NULL
)
-- Create sample data
insert into #GenderTable (Name, Gender) values
('Adam', 'M'),
('Ben', 'M'),
('Casesar', 'M'),
('Alice', 'F'),
('Beatrice', 'F'),
('Cecilia', 'F')
SELECT * FROM #GenderTable
SELECT * FROM #GenderTable
order by ROW_NUMBER() over (partition by gender order by name), Gender
DROP TABLE #GenderTable
This gives the output
Name Gender
Adam M
Ben M
Casesar M
Alice F
Beatrice F
Cecilia F
and
Name Gender
Alice F
Adam M
Beatrice F
Ben M
Cecilia F
Casesar M
If you use another DBMS the syntax may differ.
I think the best way to do it would be to have two queries (one for M, one for F) and then join them together. The catch would be you would have to calculate the "rank" of each query and then sort accordingly.
Something like the following should do what you need:
select * from
(select
#rownum:=#rownum+1 rank,
t.*
from people_table t,
(SELECT #rownum:=0) r
where t.gender = 'M'
union
select
#rownum:=#rownum+1 rank,
t.*
from people_table t,
(SELECT #rownum:=0) r
where t.gender = 'F') joined
order by joined.rank, joined.gender;
If you are using SQL Server, you can seed your two tables with an IDENTITY column as follows. Make one odd and one even and then union and sort by this column.
Note that you can only truly alternate if there are the same number of male and female records. If there are more of one than the other, you will end up with non-alternating rows at the end.
CREATE TABLE MaleTable(Id INT IDENTITY(1,2) NOT NULL, Gender CHAR(1) NOT NULL)
INSERT INTO MaleTable(Gender) SELECT 'M'
INSERT INTO MaleTable(Gender) SELECT 'M'
INSERT INTO MaleTable(Gender) SELECT 'M'
CREATE TABLE FemaleTable(Id INT IDENTITY(2,2) NOT NULL, Gender CHAR(1) NOT NULL)
INSERT INTO FemaleTable(Gender) SELECT 'F'
INSERT INTO FemaleTable(Gender) SELECT 'F'
INSERT INTO FemaleTable(Gender) SELECT 'F'
SELECT u.Id
,u.Gender
FROM (
SELECT Id, Gender
FROM FemaleTable
UNION
SELECT Id, Gender
FROM MaleTable
) u
ORDER BY u.Id ASC
See here for a working example
the code I wrote only tells me how many students have the same age. I want their names too...
SELECT YEAR(CURRENT DATE-DATEOFBIRTH) AS AGE, COUNT(*) AS HOWMANY
FROM STUDENTS
GROUP BY YEAR(CURRENT DATE-DATEOFBIRTH);
this returns something like this:
AGE HOWMANY
--- -------
21 3
30 5
Thank you.
TABLE STUDENTS COLUMNS:
StudentID (primary key), Name(varchar), Firstname(varchar), Dateofbirth(varchar)
I was thinking of maybe using the code above and somewhere add the function concat that will put the stundents' names on the same row as in
your existing SQL looks like it has errors, but you could use GROUP_CONCAT:
add GROUP_CONTACT(colname) as another column to fetch, then split by , in your application
The resulting data set does not appear useful on the surface based on the question unless you are looking for a listing of students, their age, and how many other students are of the same age:
SELECT NAME, AGE, HOWMANY
FROM STUDENTS AS S,
(SELECT YEAR(CURRENT DATE-DATEOFBIRTH) AS AGE,
COUNT(*) AS HOWMANY
FROM STUDENTS
GROUP BY YEAR(CURRENT DATE-DATEOFBIRTH)
) AS A
WHERE YEAR(CURRENT DATE-S.DATEOFBIRTH) = A.AGE
Basically perform a self-join with the age counts you have calculated.
What about...
SELECT name FROM students WHERE age = ENTER_AGE_HERE;
You have the names and the number of students can be found by finding the number of entries you get from the query.
For example, in PHP, you can find the length of the array.
Of course, you have to change to names in my example to the names used in your database.
CREATE TABLE #Student
(
id int identity(1,1),
age int,
name varchar(255)
)
INSERT INTO #Student S
VALUES(21,'bob'),
(21,'tom'),
(21,'dick'),
(21,'william'),
(35,'mark'),
(35,'anthony')
SELECT age,COUNT(*),STUFF(
(
SELECT ',' + name
FROM #Student SS
WHERE SS.age = S.age
FOR XML PATH('')
), 1, 1, '')
FROM #Student s
GROUP BY age