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Explain Connect by Prior ?
Retrieves rows in hierarchical order.e.g. select empno, ename from emp where.
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Difference between SUBSTR and INSTR ?
INSTR (String1,String2(n,(m)),INSTR returns the position of the mth occurrence of the string 2 instring1. The search begins from nth position of string1.SUBSTR (String1 n,m)SUBSTR returns a character string of size m in string1, starting from nth position of string1.
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Explain UNION,MINUS,UNION ALL, 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 queryUNION ALL - returns all rows selected by either query, including all duplicates.
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What is Referential Integrity ?
Maintaining data integrity through a set of rules that restrict the values of one or more columns of the tables based on the values of primary key or unique key of the referenced table.
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What are the usage of SAVEPOINTS ?
SAVEPOINTS are used to subdivide a transaction into smaller parts. It enables rolling back part of a transaction. Maximum of five save points are allowed.
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What are the data types allowed in a table ?
CHAR,VARCHAR2,NUMBER,DATE,RAW,LONG and LONG RAW.
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How many LONG columns are allowed in a table ? Is it possible to use LONG columns in WHERE clause or ORDER BY ?
Only one LONG columns is allowed. It is not possible to use LONG column in WHERE or ORDER BY clause.
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Where the integrity constraints are stored in Data Dictionary ?
The integrity constraints are stored in USER_CONSTRAINTS.
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How will you a activate/deactivate integrity constraints ?
The integrity constraints can be enabled or disabled by ALTER TABLE ENABLE constraint/DISABLE constraint.
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What is CYCLE/NO CYCLE in a Sequence ?
CYCLE specifies that the sequence continues to generate values after reaching either maximum or minimum value. After pan ascending sequence reaches its maximum value, it generates its minimum value. After a descending sequence reaches its minimum, it generates its maximum.NO CYCLE specifies that the sequence cannot generate more values after reaching its maximum or minimum...
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What is ROWID ?
ROWID is a pseudo column attached to each row of a table. It is 18 character long, blockno, rownumber are the components of ROWID.
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SQL*Plus interview Questions
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