PLSQL interview questions - part1

PL/SQL Interview Questions

oracle pl sql interview questions for 3+ years experience

1. Tell me about yourself
2. What is difference between TRUNCATE & DELETE?
1. Truncate is a DDL command
2. We can remove bulk amount of records at a time
3. We can't rollback the records
4. Release the space in database
5. Truncate reset the high water mark
6. Truncate explicitly commit
                                                 1. Delete is a DML command
                                                 2. We can delete record by record
                                                 3. We can rollback the records
                                                 4. Can’t release the memory in database
                                                 5. Delete can’t reset the water mark
                                                 6. Delete implicitly commit
                                              (OR)
Ans: Differences:
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.
3. Difference between view and materialized view
Difference
View is a logical table
View can hold the query
We can’t create indexes on view
View will create security purpose
                                                     Mv is a physical table
                                                     Mv can hold the query with refresh data
                                                     We can create indexes on mv
                                                     Mv will create performance issues
4. Difference between procedure and function?
Procedure:
Procedure allow the DML statements without any restrictions
We can’t call procedure in sql language
We can store images in stored procedure
Function:
Function not allow the DML statements (If you need to use we can use pragma)
We can call Function in sql language
Function can’t store images
5. What is cursor?
Cursor is private sql area which is used to execute sql statements and store processing information
6. What is explicit and implicit cursor and examples?
The implicit cursor is automatically declared by oracle every time an sql statement is executed whenever you issue a sql statement, the oracle server opens an area of memory in which the command is parsed and executed. Every implicit cursor attribute start with sql%.
An explicit cursor is created and managed by the user. And used for multi row select statement.     
7.What do u understand by database and what is objects in oracle
Ans: A database is defined as a collection of meaningful data. Objects in oracle means Table, Views, Procedures, Triggers, Synonym etc
8.What is a table, view, snapshot?
Table: A table is the basic unit of data storage in an Oracle database. The tables of a database hold all of the user accessible data. Table data is stored in rows and columns.a
Views: A view is a virtual table. Every view has a query attached to it. (The query is a SELECT statement that identifies the columns and rows of the table(s) the view uses.)
Snapshot: A Snapshot is a recent copy of a table from database or in some cases ,a subset of rows/columns of a table. It is also known as Materialized view.
9.Do a view contain data?            
Ans: Views do not contain or store data
What are the advantages of views?
Ans: Provide an additional level of table security, by restricting access to a predetermined set of rows and columns of a table.
- Hide data complexity.
- Simplify commands for the user.
- Present the data in a different perspective from that of the base table.
- Store complex queries.
10.What is an Oracle sequence?
Ans: A Sequence generates a serial list of unique numbers for numerical columns of a database's tables.
11.What is a synonym?
Ans: A synonym is an alias for a table, view, sequence or program unit.
12.What are the types of synonyms?
Ans: There are two types of synonyms private and public.
13.What is a private synonym?
Ans: Only its owner can access a private synonym.
14.What is a public synonym?
Ans: Any database user can access a public synonym
15.What is an Oracle index?
Ans: An index is an optional structure associated with a table to have direct access to rows, which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table. Index may also be considered as a ordered list of content of a column.
16.What is a schema?
Ans: The set of objects owned by user account is called the schema.
17.What is a join? Explain the different types of joins?
Ans: Join is a query, which retrieves related columns or rows from multiple tables.
Self Join          - Joining the table with itself.
Equi Join         - Joining two tables by equating two common columns.
Non-Equi Join - Joining two tables by not 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 table.
18.Difference between SUBSTR and INSTR?
Ans: 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.
19.What is difference between CHAR and VARCHAR2? What is the maximum SIZE allowed for each type?
Ans: 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
20.How to access the current value and next value from a sequence?
Ans: Current Value : Sequence name.CURRVAL
Next Value sequence name.NEXTVAL.


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