I have a student table that has three columns
1. Student Name
2. Class Name
3. Test result
A student takes more than one tests with different results. I am trying to get the data into another table that has
1. Stundent Name+CLass Name ( Concatenated )
2. Pass (No of tests Passed)
3. Fail (No of tests failed)
4. Absent (No of tests Absent)
I use
select count(*)
from Student
where Result in ('Passed')
group by StuName, ClassName;
to get the count of passed subject for each stu+class combination. Similarly for failed and absent tests.
How should I modify the code to make an insert into the Table two??
MySQL supports inline IF statement,
SELECT CONCAT(StudentName, ' ', ClassName) Student_Class,
SUM(test = 'PASSED') totalPass,
SUM(test = 'Failed') totalFailed,
SUM(test = 'Absent') totalAbsent
FROM student
GROUP BY CONCAT(StudentName, ' ', ClassName)
and when you want to insert the result from the query above, use INSERT INTO..SELECT statement,
INSERT INTO tableNAME(col1, totalPass, totalFailed, totalAbsent)
SELECT CONCAT(StudentName, ' ', ClassName) Student_Class,
SUM(test = 'PASSED') totalPass,
SUM(test = 'Failed') totalFailed,
SUM(test = 'Absent') totalAbsent
FROM student
GROUP BY CONCAT(StudentName, ' ', ClassName)
You can easily pivot the data using an aggregate function with a CASE:
select concat(StuName, ',', ClassName) StuNameClass,
sum(case when result = 'Passed' then 1 else 0 end) Passed,
sum(case when result = 'Fail' then 1 else 0 end) Fail,
sum(case when result = 'Absent' then 1 else 0 end) Absent
from Student
group by concat(StuName, ',', ClassName);
Then if you want to insert the data into your other table:
insert into Table2 (StudentClassName, Passed, Fail, Absent)
select concat(StuName, ',', ClassName) StuNameClass,
sum(case when result = 'Passed' then 1 else 0 end) Passed,
sum(case when result = 'Fail' then 1 else 0 end) Fail,
sum(case when result = 'Absent' then 1 else 0 end) Absent
from Student
group by concat(StuName, ',', ClassName);
INSERT INTO t (name_class, passed_count, failed_count, absent_count)
SELECT CONCAT(StuName, ' ', ClassName) AS name_class,
SUM(IF(Result='Passed', 1, 0)) AS passed_count,
SUM(IF(Result='Failed', 1, 0)) AS failed_count,
SUM(IF(Result='Absent', 1, 0)) AS absent_count
FROM Student
GROUP BY StuName, ClassName;
Related
How do I create an entirely new column in SQL while using CASE WHEN, GROUPING_ID(), and ROLLUP() syntax?
So far I have tried:
SELECT Country, ContactTitle, COUNT(ContactTitle) AS Count
,CASE(
WHEN
GROUPING_ID(Legend) = 0 THEN ' '
WHEN
GROUPING_ID(Legend) = 1 THEN 'SUBTOTAL(Country)')
GROUP BY ROLLUP(Country, ContactTitle)
FROM dbo.Customers
SELECT Country, ContactTitle, COUNT(ContactTitle) AS Count,
CASE
WHEN GROUPING_ID(Country,ContactTitle) = 0 THEN ''
WHEN GROUPING_ID(Country,ContactTitle) = 1 THEN CONCAT('Subtotal for ',Country)
END AS Legend
FROM dbo.Customers
GROUP BY ROLLUP(Country, ContactTitle);
A CASE needs an END.
And while testing, you could output the GROUPING_ID or GROUPING to understand what they return.
SELECT Country, ContactTitle, COUNT(*) AS Count,
(CASE
WHEN GROUPING_ID(Country, ContactTitle) = 1
THEN CONCAT('SUBTOTAL(',Country,')')
WHEN GROUPING(Country) = 1
THEN 'TOTAL'
ELSE ' '
END) AS Legend
FROM Customers
GROUP BY Country, ContactTitle WITH ROLLUP;
In this code its able to alias each case statement separately like,
SELECT
id,
SUM(CASE
WHEN (a.place = 'CHN' AND a.salary = 20000)
THEN '1'
ELSE '0'
END) AS '20K Salary',
SUM(CASE
WHEN (a.place = 'CHN' and a.salary = 35000)
THEN '1'
ELSE '0'
END) AS '35K Salary'
FROM Employee a;
but when nested CASE statement is used,
SELECT
id,
SUM(CASE
WHEN (a.place = 'CHN')
THEN (CASE
WHEN a.salary = 20000
THEN '1'
ELSE '0'
END) AS '20K Salary',
(CASE
WHEN a.salary = 35000
THEN '1'
ELSE '0'
END) AS '35K Salary'
END)
FROM Employee a;
its not possible to execute the query
In the first set of code each case statement is part of the SELECT list (i.e. they are in a comma separated list following SELECT) so each returns a column. In the second set of code there is only one case statement in the SELECT list, the fact that it is nested has no impact on this. Also the syntax for the nested case isn't correct because the THEN part is followed by two expressions separated by commas which is not allowed.
Of course this is possible to do what you want. You want to create two columns, so each needs its own logic and its own alias:
SELECT id,
SUM(CASE WHEN a.place = 'CHN' AND a.salary = 20000 THEN 1 ELSE 0
END) as Salary_20K,
SUM(CASE WHEN a.place = 'CHN' AND a.salary = 35000 THEN 1 ELSE 0
END) as Salary_35K
FROM Employee a;
Note: Don't put numeric constants in single quotes. Only use single quotes for string and date constants.
I am solving a problem very similar to this only in my case, I am not summing any values.
I have been able to write a select that works using solution from this page
SELECT
id,
GROUP_CONCAT(if(colID = 1, value, NULL)) AS 'First Name',
GROUP_CONCAT(if(colID = 2, value, NULL)) AS 'Last Name',
GROUP_CONCAT(if(colID = 3, value, NULL)) AS 'Job Title'
FROM tbl
GROUP BY id;
However, I want to omit rows that have the value to be null
I assume you want to drop the result row if any of the source rows has value IS NULL.
You should be able to achieve that with bit_and() in the HAVING clause:
SELECT id
, max(CASE WHEN colID = 1 THEN value END) AS fn
, max(CASE WHEN colID = 2 THEN value END) AS ln
, max(CASE WHEN colID = 3 THEN value END) AS jt
FROM tbl
GROUP BY id
HAVING bit_and(value IS NOT NULL);
Alternative:
...
HAVING count(*) = count(value);
I didn't spell out ELSE NULL in the CASE statements because (per documentation):
If there was no matching result value, the result after ELSE is returned, or NULL if there is no ELSE part.
Just add this constraint to the where statement of your query, like this:
SELECT
id,
GROUP_CONCAT(if(colID = 1, value, NULL)) AS 'First Name',
GROUP_CONCAT(if(colID = 2, value, NULL)) AS 'Last Name',
GROUP_CONCAT(if(colID = 3, value, NULL)) AS 'Job Title'
FROM tbl
WHERE value IS NOT NULL
GROUP BY id;
EDIT
After some tests I could make a solution to work, but it seems interesting why value is not null won't work.
Solution link: http://sqlfiddle.com/#!2/b7a445/3
SELECT
id,
max(case when colID = 1 then value else '' end) AS fn,
max(case when colID = 2 then value else '' end) AS ln,
max(case when colID = 3 then value else '' end) AS jt
FROM tbl
where not exists (select * from tbl b where tbl.id=b.id and value is null)
group by id
I am trying to get the count of females and males in the gender field of a table.
Is there a way to get the count of each in one query?
Something like:
select * from table count(where gender = 'm') as total_males, count(where gender = 'f') as total_females;
or will it require two queries?
select count(*) from table where gender = 'm';
select count(*) from table where gender = 'f';
This is basically a PIVOT. MySQL does not have a pivot so you can use an aggregate function with a CASE statement to perform this:
select
sum(case when gender = 'm' then 1 else 0 end) Total_Male,
sum(case when gender = 'f' then 1 else 0 end) Total_Female
from yourtable
See SQL Fiddle with Demo
Or using COUNT:
select
count(case when gender = 'm' then 1 else null end) Total_Male,
count(case when gender = 'f' then 1 else null end) Total_Female
from yourtable;
See SQL Fiddle with Demo
Something like this will work:
SELECT SUM(IF(t.gender='m',1,0)) AS total_males
, SUM(IF(t.gender='f',1,0)) AS total_females
FROM mytable t
The "trick" here is that we are using a conditional test to return either a 0 or a 1 for each row, and then adding up the 0's and 1's. To make this a little more clear, I am using the SUM aggregate function rather than COUNT, although COUNT could be used just as easily, though we'd need to return a NULL in place of the zero.
SELECT COUNT(IF(t.gender='m',1,NULL)) AS total_males
, COUNT(IF(t.gender='f',1,NULL)) AS total_females
FROM mytable t
Consider that the two expressions in the SELECT list of this query:
SELECT COUNT(1)
, SUM(1)
FROM mytable t
Will return the same value.
If you want to avoid the MySQL IF function, this can also be done using the ANSI SQL CASE expression:
SELECT SUM( CASE WHEN t.gender = 'm' THEN 1 ELSE 0 END )) AS total_males
, SUM( CASE WHEN t.gender = 'f' THEN 1 ELSE 0 END )) AS total_females
FROM mytable t
select sum(case when gender='m' then 1 else null end) as total_males, sum(case when gender='f' then 1 else null end) as total_females from ...
Should work just fine!
If your only issue is to avoid two queries, you can always write two queries as subselects of one query.
Select (select 1 from dual) as one, (select 2 from dual) as two from dual
This would work for your scenario, too.
I have a column 'hour'
I have a column 'kind' (it can be 1,2 or 3)
I'd like to do something like:
SELECT count(id), SUM(hour) as totHour, SUM( IF ( kind = 1, 1, 0 ) ) as countKindOne
or
SELECT count(id), SUM(hour) as totHour, COUNT( IF ( kind = 1 ) ) as countKindOne
But mysql tell me I've an error... what's the error!?
Please see this stackoverflow topic: MySQL SUM IF field b = field a
.. I'm not able to reply this ...
You can use a CASE statement:
SELECT count(id),
SUM(hour) as totHour,
SUM(case when kind = 1 then 1 else 0 end) as countKindOne
you want something like:
SELECT count(id), SUM(hour) as totHour, SUM(kind=1) as countKindOne;
Note that your second example was close, but the IF() function always takes three arguments, so it would have had to be COUNT(IF(kind=1,1,NULL)). I prefer the SUM() syntax shown above because it's concise.
You can also use SUM + IF which is shorter than SUM + CASE:
SELECT
count(id)
, SUM(IF(kind=1, 1, 0)) AS countKindOne
, SUM(CASE WHEN kind=2 THEN 1 ELSE 0 END) AS countKindTwo
There is a slight difference between the top answers, namely SUM(case when kind = 1 then 1 else 0 end) and SUM(kind=1).
When all values in column kind happen to be NULL, the result of SUM(case when kind = 1 then 1 else 0 end) is 0, whereas the result of SUM(kind=1) is NULL.
An example (http://sqlfiddle.com/#!9/b23807/2):
Schema:
CREATE TABLE Table1
(`first_col` int, `second_col` int)
;
INSERT INTO Table1
(`first_col`, `second_col`)
VALUES
(1, NULL),
(1, NULL),
(NULL, NULL)
;
Query results:
SELECT SUM(first_col=1) FROM Table1;
-- Result: 2
SELECT SUM(first_col=2) FROM Table1;
-- Result: 0
SELECT SUM(second_col=1) FROM Table1;
-- Result: NULL
SELECT SUM(CASE WHEN second_col=1 THEN 1 ELSE 0 END) FROM Table1;
-- Result: 0
From MYSQL I solved the problem like this:
SUM(CASE WHEN used = 1 THEN 1 ELSE 0 END) as amount_one,
Hope this helps :D
It is worth noting that you can build upon Gavin Toweys answer by using multiple fields from across your query such as
SUM(table.field = 1 AND table2.field = 2)
You can also use this syntax for COUNT and I am sure other functions as well.