SQL*Plus Statements 2

106. Explain CONNECT BY PRIOR?
Retrieves rows in hierarchical order eg.
select empno, ename from emp where.

107. 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.

108. 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 duplicates.

109. 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.

110. What is the fastest way of accessing a row in a table?
Using ROWID.
CONSTRAINTS