Oracle: Overwrite values in a column with the longest string - sql

Question

I’m running into a problem.
Say, I have columns called “C1, C2, C3....” in a table. I’d like to use the longest string in C1 to replace every other cells in C1 column without disturbing other columns.
I tired several ways but I cannot get my Oracle code run. Could someone please show me a sample code to do this problem? I typed my question using a cellphone so I apologize for not showing you my code. But I think my description is fine... Thank you!

Answer 1

I would use window functions. Oracle has a very convenient functionality with keep:
select max(col1) keep (dense_rank first order by len(col1) desc) over () as col1,
col2, col3, . . .
from t;
You can incorporate this into an update:
update t
set col1 = (select select max(col1) keep (dense_rank first order by len(col1) desc) over () as col1
from t
);

Answer 2

For example:
SQL> select * from test;
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
20 RESEARCH DALLAS
30 SALES CHICAGO
40 OPERATIONS BOSTON
SQL> update test set
2 dname = (select max(dname) --> MAX fixes TOO-MANY-ROWS because ACCOUNTING
3 from test -- and OPERATIONS have same length
4 where length(dname) = (select max(length(dname))
5 from test
6 )
7 );
4 rows updated.
SQL> select * from test;
DEPTNO DNAME LOC
---------- -------------- -------------
10 OPERATIONS NEW YORK
20 OPERATIONS DALLAS
30 OPERATIONS CHICAGO
40 OPERATIONS BOSTON
SQL>
[EDIT, GROUP BY]
Another example is based on a different table, which reflects what you described in a comment. The DEPTNO (department number) is used to "group" employees, and I'm going to update the JOB column value to the longest job name within that department.
Query is similar to the previous one; it just joins appropriate columns (DEPTNO) throughout code.
Sample data:
SQL> select * from test order by deptno, ename;
DEPTNO ENAME JOB
---------- ---------- ---------
10 CLARK MANAGER
KING PRESIDENT --> the longest in DEPTNO = 10
MILLER CLERK
20 ADAMS CLERK
FORD ANALYST
JONES MANAGER --> as long as ANALYST, but MAX(JOB) will return this value
SCOTT ANALYST
SMITH CLERK
30 ALLEN SALESMAN --> the longest in DEPTNO = 30
BLAKE MANAGER
JAMES CLERK
MARTIN SALESMAN
TURNER SALESMAN
WARD SALESMAN
Update and the result:
SQL> update test t set
2 t.job = (select max(t1.job)
3 from test t1
4 where t1.deptno = t.deptno
5 and length(t1.job) = (select max(length(t2.job))
6 from test t2
7 where t2.deptno = t1.deptno
8 )
9 );
14 rows updated.
SQL> select * from test order by deptno, ename;
DEPTNO ENAME JOB
---------- ---------- ---------
10 CLARK PRESIDENT
KING PRESIDENT
MILLER PRESIDENT
20 ADAMS MANAGER
FORD MANAGER
JONES MANAGER
SCOTT MANAGER
SMITH MANAGER
30 ALLEN SALESMAN
BLAKE SALESMAN
JAMES SALESMAN
MARTIN SALESMAN
TURNER SALESMAN
WARD SALESMAN