What command is used to create a table by
copying the structure of another table?
CREATE TABLE .. AS SELECT command
To copy only the structure, the WHERE clause of the SELECT command
should contain a FALSE statement as in the following.
CREATE TABLE NEWTABLE AS SELECT * FROM EXISTINGTABLE WHERE 1=2;
If the WHERE condition is true, then all the rows or rows satisfying the
condition will be copied to the new table.
TRUNCATE TABLE EMP; DELETE FROM EMP; Will the outputs of the above two
Both will result in deleting all the rows in the table EMP..
What is the output of the following query SELECT TRUNC(1234.5678,-2)
What are the wildcards used for pattern matching.?
_ for single character substitution and % for multi-character
What is the parameter substitution symbol used with INSERT INTO command?
What's an SQL injection?
SQL Injection is when form data contains an SQL escape sequence and
injects a new SQL query to be run.
What is difference between TRUNCATE & DELETE ?
TRUNCATE commits after deleting entire table i.e., cannot be rolled
back. Database triggers do not fire on TRUNCATE
DELETE allows the filtered deletion. Deleted records can be rolled back
or committed. Database triggers fire on DELETE.
What is a join? Explain the different types of joins?
Join is a query, which retrieves related columns or rows from multiple
Self Join - Joining the table with itself.
Equi Join - Joining two tables by equating two common columns.
Non-Equi Join - Joining two tables by equating two common columns.
Outer Join - Joining two tables in such a way that query can also
retrieve rows that do not have corresponding join value in the other
What is the sub-query?
Sub-query is a query whose return values are used in filtering
conditions of the main query.
What is correlated sub-query?
Correlated sub-query is a sub-query, which has reference to the main
Explain CONNECT BY PRIOR?
Retrieves rows in hierarchical order eg.
select empno, ename from emp where.
Difference between SUBSTR and INSTR?
INSTR (String1, String2 (n, (m)),
INSTR returns the position of the m-th occurrence of the string 2 in
string1. The search begins from nth position of string1.
SUBSTR (String1 n, m)
SUBSTR returns a character string of size m in string1, starting from n-th
position of string1.
Explain UNION, MINUS, UNION ALL and INTERSECT?
INTERSECT - returns all distinct rows selected by both queries. MINUS -
returns all distinct rows selected by the first query but not by the
second. UNION - returns all distinct rows selected by either query UNION
ALL - returns all rows selected by either query, including all
What is ROWID?
ROWID is a pseudo column attached to each row of a table. It is 18
characters long, blockno, rownumber are the components of ROWID.
What is the fastest way of accessing a row in a table?