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Oracle Materials-Free Download
1. What are Schema Objects?
A schema is said to be a collection of the logical structures of schema objects or data. A schema has the same name as that user and is owned by the database user. Schema objects are manipulated and created with SQL which comprises of the following object types: Clusters, Database links, Dimensions, Indexes, Java sources, Tables, Views, Operators, Sequences, Synonyms, etc.
2. What is the difference between varchar & varchar2 data types?
Varchar is capable of storing up to 2000 bytes whereas Varchar2 stores up to 4000 bytes. Varchar occupies space for NULL values and Varchar2 won’t occupy any space. Both are different with respect to space.
3. In what language Oracle has been built?
Oracle is developed with the use of C language
4. What is known as Raw datatype?
Raw datatype has been used to store the values in the binary data format. The maximum size for a raw present in a table is said to be 32767 bytes.
5. Define the use of NVL function
The NVL function has been used for replacing the NULL values using given value or another value. For e.g., NVL(Value, replace value)
6. What commands are used for months calculation?
In Oracle, the months_between function has been used to identify the number of months which exists between the given dates. For e.g., Months_between(Date 1, Date 2)
7. Define nested tables
The nested table is referred as a data type in Oracle. It has been used to support columns which comprise of multi-valued attributes. Also, it holds all the subtable.
8. What is known as COALESCE function?
COALESCE function is used for returning the value that is set to be null present in the list. If all values in the list are said to be null, then the coalesce function returns NULL.
Coalesce(value1, value2, value3, …)
9. Define BLOB datatype
A BLOB datatype is considered to be a varying length binary string that has been used for storing two gigabytes memory. Length must be particularly in Bytes for the BLOB.
10. How will we represent comments in Oracle?
Comments in Oracle are represented in two ways. They are
1. Single statement: Two dashes(-) before starting the line.
2. Block of statement: /*¬¬¬–*/ has been used to represent it as comments.
3. Describe the difference between Replace and Translate?
Replace has been used to substitute a single character using a word whereas the Translate has been used for the character by character substitution.
12. Define DML
DML is known as Data Manipulation Language which is used to manipulate and access data in the existing objects. DML statements include select, insert, delete and update. It will not entirely commit the current transaction.
13. How can we display rows in the table without the duplicates?
Duplicate rows may be removed with the help of the keyword DISTINCT in the select statement.
14. Define the usage of Merge statement
Merge statement is said to be used for selecting rows from one or more data source for the purpose of insertion and updating into a table or view. It is used to merge multiple operations.
15. What is referred as a NULL value in Oracle?
NULL value represents unknown or missing data. This has been used as a placeholder or it is represented in as the default entry in order to indicate which there has no actual data present.
16. What is known as USING Clause? Give example.
The USING clause has been used to represent the column to test for equality if two tables are joined together.
[sql]Select * from the employee to join salary using the employee ID[/sql]
Employee tables join the Salary tables using the Employee ID.
17. Define the Key preserved table
A table has been set to be a key-preserved table if every table key may also be the result key of the join. It guarantees to return the only single copy of each row from the base table.
18. What is referred as WITH CHECK option?
The WITH CHECK option clause refers the check level to be done in the DML statements. It has been used to prevent the changes to a view which would deliver results that are not contained in the subquery.
19. What is the use of the aggregate functions in Oracle?
An aggregate function is said to be a function where the values of the multiple records or rows have been combined together to obtain a single value output. The common aggregate functions include average, count, sum.
20. What is known as GROUP BY clause?
A GROUP BY clause has been used in choosing the statement where it gathers data from the multiple records and collects the results by one or more columns.
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