1. To see current user name
Sql> show user;
2. Change SQL prompt name
SQL> set sqlprompt “Manimara > “
Manimara >
Manimara >
3. Switch to DOS prompt
SQL> host
4. How do I eliminate the duplicate rows ?
SQL> delete from table_name where rowid not in (select max(rowid) from table group by duplicate_values_field_name);
or
SQL> delete duplicate_values_field_name dv from table_name ta where rowid <(select min(rowid) from table_name tb where ta.dv=tb.dv); Example. Table Emp Empno Ename 101 Scott 102 Jiyo 103 Millor 104 Jiyo 105 Smith delete ename from emp a where rowid < ( select min(rowid) from emp b where a.ename = b.ename); The output like, Empno Ename 101 Scott 102 Millor 103 Jiyo 104 Smith 5. How do I display row number with records? To achive this use rownum pseudocolumn with query, like SQL> SQL> select rownum, ename from emp;
Output:
1 Scott
2 Millor
3 Jiyo
4 Smith
6. Display the records between two range
select rownum, empno, ename from emp where rowid in
(select rowid from emp where rownum <=&upto minus select rowid from emp where rownum<&Start); Enter value for upto: 10 Enter value for Start: 7 ROWNUM EMPNO ENAME --------- --------- ---------- 1 7782 CLARK 2 7788 SCOTT 3 7839 KING 4 7844 TURNER 7. I know the nvl function only allows the same data type(ie. number or char or date Nvl(comm, 0)), if commission is null then the text “Not Applicable” want to display, instead of blank space. How do I write the query? SQL> select nvl(to_char(comm.),'NA') from emp;
Output :
NVL(TO_CHAR(COMM),'NA')
-----------------------
NA
300
500
NA
1400
NA
NA
8. Oracle cursor : Implicit & Explicit cursors
Oracle uses work areas called private SQL areas to create SQL statements.
PL/SQL construct to identify each and every work are used, is called as Cursor.
For SQL queries returning a single row, PL/SQL declares all implicit cursors.
For queries that returning more than one row, the cursor needs to be explicitly declared.
9. Explicit Cursor attributes
There are four cursor attributes used in Oracle
cursor_name%Found, cursor_name%NOTFOUND, cursor_name%ROWCOUNT, cursor_name%ISOPEN
10. Implicit Cursor attributes
Same as explicit cursor but prefixed by the word SQL
SQL%Found, SQL%NOTFOUND, SQL%ROWCOUNT, SQL%ISOPEN
Tips : 1. Here SQL%ISOPEN is false, because oracle automatically closed the implicit cursor after executing SQL statements.
: 2. All are Boolean attributes.
11. Find out nth highest salary from emp table
SELECT DISTINCT (a.sal) FROM EMP A WHERE &N = (SELECT COUNT (DISTINCT (b.sal)) FROM EMP B WHERE a.sal<=b.sal); Enter value for n: 2 SAL --------- 3700 12. To view installed Oracle version information SQL> select banner from v$version;
13. Display the number value in Words
SQL> select sal, (to_char(to_date(sal,'j'), 'jsp'))
from emp;
the output like,
SAL (TO_CHAR(TO_DATE(SAL,'J'),'JSP'))
--------- -----------------------------------------------------
800 eight hundred
1600 one thousand six hundred
1250 one thousand two hundred fifty
If you want to add some text like,
Rs. Three Thousand only.
SQL> select sal "Salary ",
(' Rs. '|| (to_char(to_date(sal,'j'), 'Jsp'))|| ' only.'))
"Sal in Words" from emp
/
Salary Sal in Words
------- ------------------------------------------------------
800 Rs. Eight Hundred only.
1600 Rs. One Thousand Six Hundred only.
1250 Rs. One Thousand Two Hundred Fifty only.
14. Display Odd/ Even number of records
Odd number of records:
select * from emp where (rowid,1) in (select rowid, mod(rownum,2) from emp);
1
3
5
Even number of records:
select * from emp where (rowid,0) in (select rowid, mod(rownum,2) from emp)
2
4
6
15. Which date function returns number value?
months_between
16. Any three PL/SQL Exceptions?
Too_many_rows, No_Data_Found, Value_Error, Zero_Error, Others
17. What are PL/SQL Cursor Exceptions?
Cursor_Already_Open, Invalid_Cursor
18. Other way to replace query result null value with a text
SQL> Set NULL ‘N/A’
to reset SQL> Set NULL ‘’
19. What are the more common pseudo-columns?
SYSDATE, USER , UID, CURVAL, NEXTVAL, ROWID, ROWNUM
20. What is the output of SIGN function?
1 for positive value,
0 for Zero,
-1 for Negative value.
21. What is the maximum number of triggers, can apply to a single table?
12 triggers.
More Oracle Questions
What is a CO-RELATED SUBQUERY
A CO-RELATED SUBQUERY is one that has a correlation name as table or view designator in the FROM clause of the outer query and the same correlation name as a qualifier of a search condition in the WHERE clause of the subquery.
2. eg
3. SELECT field1 from table1 X
4. WHERE field2>(select avg(field2) from table1 Y
5. where
field1=X.field1);
(The subquery in a correlated subquery is revaluated for every row of the table or view named in the outer query.)
What are various joins used while writing SUBQUERIES
Self join-Its a join foreign key of a table references the same table.
Outer Join–Its a join condition used where One can query all the rows of one of the tables in the join condition even though they don’t satisfy the join condition.
Equi-join–Its a join condition that retrieves rows from one or more tables in which one or more columns in one table are equal to one or more columns in the second table.
What are various constraints used in SQL
NULL
NOT NULL
CHECK
DEFAULT
What are different Oracle database objects
TABLES
VIEWS
INDEXES
SYNONYMS
SEQUENCES
TABLESPACES etc
What is difference between Rename and Alias
Rename is a permanent name given to a table or column whereas Alias is a temporary name given to a table or column which do not exist once the SQL statement is executed.
What is a view
A view is stored procedure based on one or more tables, its a virtual table.
What are various privileges that a user can grant to another user
SELECT
CONNECT
RESOURCE
What is difference between UNIQUE and PRIMARY KEY constraints
A table can have only one PRIMARY KEY whereas there can be any number of UNIQUE keys. The columns that compose PK are automatically define NOT NULL, whereas a column that compose a UNIQUE is not automatically defined to be mandatory must also specify the column is NOT NULL.
Can a primary key contain more than one columns
Yes
How you will avoid duplicating records in a query
By using DISTINCT
What is difference between SQL and SQL*PLUS
SQL*PLUS is a command line tool where as SQL and PL/SQL language interface and reporting tool. Its a command line tool that allows user to type SQL commands to be executed directly against an Oracle database. SQL is a language used to query the relational database(DML,DCL,DDL). SQL*PLUS commands are used to format query result, Set options, Edit SQL commands and PL/SQL.
Which datatype is used for storing graphics and images
LONG RAW data type is used for storing BLOB’s (binary large objects).
How will you delete duplicating rows from a base table
DELETE FROM table_name A WHERE rowid>(SELECT min(rowid) from table_name B where B.table_no=A.table_no);
CREATE TABLE new_table AS SELECT DISTINCT * FROM old_table;
DROP old_table RENAME new_table TO old_table DELETE FROM table_name A WHERE rowid NOT IN (SELECT MAX(ROWID) FROM table_name GROUP BY column_name)
What is difference between SUBSTR and INSTR
SUBSTR returns a specified portion of a string eg SUBSTR(’BCDEF’,4) output BCDE INSTR provides character position in which a pattern is found in a string. eg INSTR(’ABC-DC-F’,'-’,2) output 7 (2nd occurence of ‘-’ )
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