Skip to main content

Converting Rows to Single Column


Strange solution for someone who is looking into this statement for the first time.

I have used XMLAGG, XMLELEMENT and EXTRACT functions. See if you can crack it.


XMLAGG is an aggregate/group function which aggregates all the values for a column.
XMLELEMENT is a function which creates XML tags with tag element E.
EXTRACT function then removes all the XML text and retains only text.

SELECT   deptno,  XMLAGG (XMLELEMENT (e, ename || ',')).EXTRACT ('//text()') as ENAMES
FROM
   emp
GROUP BY deptno;

 This statement will give you an output as below,







If you observe in this output, there is an extra comma at the end of the ENAMEs list. To remove this, I shall use another function RTRIM which is used to trim characters on the right side.

SELECT   deptno,  RTRIM(XMLAGG (XMLELEMENT (e, ename || ',')).EXTRACT ('//text()'),',') as ENAMES
FROM
   emp
GROUP BY deptno;







In case if the output does not show the values properly then use the following command to restrict the column length.

COLUMN ENAMES FORMAT A50
Happy Learning!!!!!!!



Comments

Post a Comment

Popular posts from this blog

SQL Interview Questions on Subqueries

SUB Queries:
1. List the employees working in research department 2. List employees who are located in New York and Chicago
3. Display the department name in which ANALYSTS are working
4. Display employees who are reporting to JONES
5. Display all the employees who are reporting to Jones Manager
6. Display all the managers in SALES and ACCOUNTING department
7. Display all the employee names in Research and Sales Department who are having at least 1 person reporting to them
8. Display all employees who do not have any reportees
9. List employees who are having at least 2 reporting
10. List the department names which are having more than 5 employees
11. List department name having at-least 3 salesman
12. List employees from research and accounting having at-least 2 reporting
13. Display second max salary
14. Display 4th max salary
15. Display 5th max salary  -- Answer for nth Max Salary
Co-Related Subqueries:
16. Write a query to get 4th max salary from EMP table
17. Write a query to get 2nd…
21 comments
Read more

'Linux-x86_64 Error: 28: No space left on device' While trying to start the database -- Error

SQL> startup mount pfile='/tmp/initdlfasp12.ora'
ORA-27102: out of memory
Linux-x86_64 Error: 28: No space left on device


This as you can see is on Linux x86 with 64 bit processor. We got this error after we changed SGA on 10gR2 database. So was sure that this is something to do with the OS.

Parameters to check for this are shmall.

shmall is the total amount of shared memory, in pages, that the system can use at one time.

$cat /proc/sys/kernel/shmmax
53687091200

$ getconf PAGE_SIZE
4096

As per Oracle SHMALL should be set to the total amount of physical RAM divided by page size.

Our system has 64GB memory, so change kernel.shmall = 1024 * 1024 * 1024 * 64 / 4096 = 16777216


Once this value is calculated you can modify Linux system configuration file directly.

$ su - root
vi /etc/sysctl.conf file:
kernel.shmall=16777216

and

# sysctl -p

Once this is done the database was started without any problem.
14 comments
Read more

Answers for SQL Functions

1. SQL> SELECT empno, ename FROM emp WHERE Length(ename) = 4;

2. SQL> SELECT empno, ename, job FROM emp where Length(job)=7;

3. SQL> SELECT Length('qspiders') - Length(replace('qspiders','s','')) FROM dual;

4. SQL>  SELECT empno, ename, job FROM emp WHERE Instr(job,'MAN') >0;

5. SQL> SELECT empno, ename, job FROM emp WHERE Instr(job, 'MAN') =1;

6. SQL> SELECT empno, ename, job FROM emp WHERE (Length(ename) - Length(Replace(ename, 'L',''))) = 1;

7. SQL> SELECT * FROM dept WHERE Instr(dname,'O') > 0;

8. SQL> SELECT Concat(ename,' working as a ') || Concat(job, ' earns ') || Concat(sal, '  in ') || Conc
at('dept ',deptno) AS text from emp;

OR

SQL> SELECT Concat(Concat(Concat(Concat(Concat(Concat(Concat(ename,' working as a '), job),' earns '), sal),'  in '),'dept '), deptno) AS text FROM emp;

9. SQL> SELECT empno, ename…
40 comments
Read more