CHAR pads blank spaces to the maximum length.
VARCHAR2 does not pad blank spaces.
For CHAR the maximum length is 255 and 2000 for VARCHAR2.
What Are The Data Types Allowed In A Table?
CHAR, VARCHAR2, NUMBER, DATE, RAW, LONG and LONG RAW.
What Is On Delete Cascade?
When ON DELETE CASCADE is specified Oracle maintains referential integrity by automatically removing dependent foreign key values if a referenced primary or unique key value is removed.
What Is 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.
What Is Referential Integrity Constraint?
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.
What Is An Integrity Constraint?
Integrity constraint is a rule that restricts values to a column in a table.
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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.
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.
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 Connect By Prior?
Retrieves rows in hierarchical order
eg: select empno, ename from emp where.
What Is Correlated Sub-query?
Correlated sub-query is a sub-query, which has reference to the main query.
What Is The Sub-query?
Sub-query is a query whose return values are used in filtering conditions of the main query.
What Is Hit Ratio?
It is a measure of well the data cache buffer is handling requests for data.
Hit Ratio = (Logical Reads – Physical Reads – Hits Misses)/ Logical Reads.
What Is A Rollback Segment Entry?
It is the set of before image data blocks that contain rows that are modified by a transaction.
Each rollback segment entry must be completed within one rollback segment.
A single rollback segment can have multiple rollback segment entries.
What Is Use Of Rollback Segments In Oracle Database?
They allow the database to maintain read consistency between multiple transactions.
What Is Advantage Of Having Disk Shadowing / Mirroring?
Shadow set of disks save as a backup in the event of disk failure. In most operating systems if any disk failure occurs it automatically switchover to place of failed disk.
Improved performance because most OS support volume shadowing can direct file I/O request to use the shadow set of files instead of the main set of files. This reduces I/O load on the main set of disks.
What Is Redo Log File Mirroring? How Can Be Achieved?
Process of having a copy of redo log files is called mirroring.
This can be achieved by creating group of log files together, so that LGWR will automatically writes them to all the members of the current on-line redo log group. If any one group fails then database automatically switch over to next group. It degrades performance.
How To Implement The Multiple Control Files For An Existing Database?
Shutdown the database
Copy one of the existing controlfile to new location
Edit Config ora file by adding new control filename
Restart the database.
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