What is wrong with this query?

select*from"EMP"where'SCOTT'="ENAME"and"DEPTNO"=20;
     EMPNO ENAME      JOB              MGR HIREDATE     
---------- ---------- --------- ---------- ---------
      7788 SCOTT      ANALYST         7566 13-JUL-87

You could write it as

select
    *
from
    "EMP"
where
    'SCOTT'="ENAME"
    and
    "DEPTNO"=20;

personnaly, I would write it as

select *
from emp
where ename='SCOTT'
  and deptno=20;

Formatting is very important, it makes your code nice to read and indentation make the blocks visualable.

Auto-formatting is also fine, but I like to decide myself if the line is too long, or if I want to have FROM and EMP on the same line.

Have a look at the free online SQL Formatter SQLinForm

I have read a long long time ago the following note on positive infinity http://www.ixora.com.au/notes/infinity.htm

Today I finally succeeded in inserting positive infinity in a number field

create table t as select 
  STATS_F_TEST(cust_gender, 1, 'STATISTIC','F') f
from (
  select 'M' cust_gender from dual union all 
  select 'M' from dual union all 
  select 'F' from dual union all 
  select 'F' from dual)
;

I am so happy

Let’s try a few queries

SQL> desc t
 Name              Null?    Type
 ----------------- -------- ------
 F                          NUMBER

SQL> select f from t;

         F
----------
         ~

SQL> select f/2 from t;
select f/2 from t
        *
ERROR at line 1:
ORA-01426: numeric overflow

SQL> select -f from t;

        -F
----------
        -~

SQL> select cast(f as binary_double) from t;

CAST(FASBINARY_DOUBLE)
----------------------
                   Inf

SQL> select * from t
  2  where cast(f as binary_double) = binary_double_infinity;

         F
----------
         ~

Now expect a lot of bugs with your oracle clients

Toad 9 for example returns

SQL>  select f from t
select f from t
              *
Error at line 1
OCI-22065: number to text translation for the given 
format causes overflow

create table t(
  deptno number, 
  firstname varchar2(10), 
  lastname varchar2(10), 
  hiredate date);

insert into t values (
  10,'Jo','Smith',date '2001-01-01');

insert into t values (
  10,'Jack','River',date '2002-02-02');

to get the latest hiredate per department

select deptno, 
  max(hiredate) hiredate
from t 
group by deptno;

    DEPTNO HIREDATE 
---------- ---------
        10 02-FEB-02

if you want to get the name of the employee at that date, you could by mistake believe the following works

select deptno, 
  max(firstname) keep (dense_rank last 
    order by hiredate) firstname,
  max(lastname) keep (dense_rank last 
    order by hiredate) lastname,
  max(hiredate) hiredate
from t
group by deptno;

    DEPTNO FIRSTNAME  LASTNAME   HIREDATE 
---------- ---------- ---------- ---------
        10 Jack       River      02-FEB-02

This will produce wrong result if hiredate is not unique

insert into t values (10,'Bob','Zhong', date '2002-02-02');
select deptno, 
  max(firstname) keep (dense_rank last 
    order by hiredate) firstname,
  max(lastname) keep (dense_rank last 
    order by hiredate) lastname,
  max(hiredate) hiredate
from t
group by deptno;

    DEPTNO FIRSTNAME  LASTNAME   HIREDATE 
---------- ---------- ---------- ---------
        10 Jack       Zhong      02-FEB-02

of course there is Jack Zhong.

To get a consistent record, it is possible to add all the columns in the order by

select deptno, 
  max(firstname) keep (dense_rank last 
    order by hiredate,firstname,lastname) firstname,
  max(lastname) keep (dense_rank last 
    order by hiredate,firstname,lastname) lastname,
  max(hiredate) hiredate
from t
group by deptno;

    DEPTNO FIRSTNAME  LASTNAME   HIREDATE 
---------- ---------- ---------- ---------
        10 Jack       River      02-FEB-02

begin
  dbms_output.put_line(
    to_char(
      timestamp '9999-12-31 23:59:59.999999999',
      'FF9SP'));
end;
/ 
NINE HUNDRED NINETY-NINE MILLION NINE HUNDRED NINETY-NINE 
THOUSAND NINE HUNDRED NINETY-NINE

Unfortunately, I could not get this in sql/10.2.0.2

select 
  to_char(
    timestamp '9999-12-31 23:59:59.999999999',
    'FF9SP') X
from
  dual;
ORA-01877: string is too long for internal buffer

Well, since the string is too long, let’s try with a LONGER string

select 
  regexp_substr(
    to_char(
      timestamp '9999-12-31 23:59:59.999999999',
'FF9SP/FMDAY MONTH DDTHSP YYYYSP A.D. HH24SP MISP SSSP')
    ,'[^/]+')X
from
  dual;

X                                                                                          
---------------------------------------------------------
----------------------------------
NINE HUNDRED NINETY-NINE MILLION NINE HUNDRED NINETY-NINE 
THOUSAND NINE HUNDRED NINETY-NINE