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A self join means in a table each row is joined to other ROWS in the table and also to itself

Here, the standard JOIN command is used in which both the tables in the join are the same tables.

SELECT T2.name

FROM category T1

JOIN category T2

ON T2.parent = T1.id

WHERE T1.name = 'Best INTERVIEW QUESTIONS.'

Here is the syntax:-

SELECT columns

FROM table1

INNER JOIN table2

ON table1.column = table2.column;

An Inner join is ALSO called a SIMPLE join, and it is the MOSTLY used join.

Left join returns all the RECORDS from the left-hand SIDE of the table which is specified in the ON condition, only those records from the right table where the join condition is met.

syntax:-

SELECT columns

FROM TABLE1

LEFT JOIN table2

ON table1.column = table2.column;

When the data required by the user is in more than one table, then JOIN comes into the picture. ORACLE Join is used to combine the rows from more than one tables. Join also retrieves data from MULTIPLE tables and creates a new table.

Dynamic SQL is the PROGRAMMING methods in which the SQL STATEMENTS are constructed at the run time. Dynamic SQL is USED when there is a requirement of the DDL(database DEFINITION language) statements while writing the programs or when the user is not aware of the compilation time of the SQL statement.

DROP constraint is used for removing the constraints from the table.

Syntax:-

ALTER TABLE table_name

DROP CONSTRAINT constraint_name

For example:- if the table NAME is INTERVIEW. QUESTIONS and the constraint name is TEST_ CONST

Once the table is created, then the user can add any value in the table, but the values have to be VALIDATED. In this case, the CONSTRAINTS act as a validator which checks the data validity.

• NOT NULL:-The column will not accept the NULL value
• UNIQUE:-It will check whether the record entered is unique or not.
• PRIMARY:-The column will have a value, and it will be unique. In a table, only one primary key should be there.
• CHECK:-when the user wants the record in the column to be of a PARTICULAR type.
• FOREIGN KEY:-to relate more than one table that means matching the value of one table with that of another table.

The translate FUNCTION replaces the characters in a string with the new set of characters one by one. For example:- the first character in the string is replaced by the first character of the original string and so on. The translate function always RETURNS a string value.

Syntax:-

TRANSLATE( STRING1, string_to_replace, replacement_string )

String1:-the string which has to be replaced

string_to_replace:-the string that has to be SEARCHED in the string 1

replacement_string:-the new string with which string1 will be replaced.

The compound trigger was in introduced in Oracle 11g. This single trigger on a table enables the user to specify the actions for each of the four timing points:

• Before the firing STATEMENT
• Before each row that the firing statement affects
• After each row that the firing statement changes
• After the firing statement

In other words, Compound trigger MERGES all the four triggering EVENTS into the single piece of CODE, and as a result, the performance of the DATABASE server is improved during the bulk operations. The Compound trigger is only for the DML triggers.

The trigger is the PROCEDURE which is IMPLICITLY executed by the Oracle SERVER when the INSERT, UPDATE, DELETE statement is executed against the associated table in the Oracle database.

Based on the EVENT these are the TYPES of trigger:-

• DDL Trigger:-INSERT/UPDATE/DELETE
• DML Trigger:-CREATE/ALTER
• DATABASE Trigger:-LOGON/LOGOFF/STARTUP/SHUTDOWN

• Character Datatypes-CHAR, VARCHAR2, VARCHAR, NCHAR, NVARCHAR2, etc
• Numeric Datatypes:-NUMBER, BINARY_FLOAT, BINARY_DOUBLE
• DATE DATATYPE:-DATE, DD-MON-YY, TIMESTAMP, etc
• LOB Datatypes:-BLOB, CLOB, NCLOB, etc
• RAW and LONG RAW Datatypes
• ROWID and UROWID Datatypes
• ANSI, DB2, and SQL/DS Datatypes
• XML Datatypes:-XMLType
• URI Datatypes:-UriType

ORACLE 12c created the change in the architecture of the ORACLE DATABASE. In this VERSION CAME with the concept of the Container Database (CDB) and the Pluggable Database (PDB)

• Container Database (CDB) :- Container database contains the Oracle Metadata.This database includes control files, data files, temp files, etc. and this includes the data dictionary for those objects which are owned by the root container.
• Pluggable Database (PDB):- Pluggable Database contains the data files and temp files to handle PDB's objects only, and this includes the data dictionary for those objects which are in PDB only.

This is the favorite interviewer question in Oracle interview questions for experienced.

An INSERT statement is USED in the ORACLE database to insert the single record or the multiple records in a table.

This particular ORACLE INTERVIEW question explains the importance of keys in the database.

SYNTAX:-

INSERT INTO table (column1, column2, ... column_n ) VALUES

(expression1, expression2, ... expression_n );

An UPDATE statement is used to update the records that already exist in the table.

SYNTAX:-

UPDATE table

SET column1 = expression1,

column2 = expression2,

  ...

column_n = expression_n

[WHERE conditions];

PL/SQL is the language which is USED to write the codes in the database.

For Example - PL/SQL is used to write the ORACLE database.PL/SQL is basically to combine the SQL and the procedural feature of the programming language. This language was developed to enhance the CHARACTERISTICS of the SQL language.

Some of the features of the PL/SQL are:-

• PL/SQL FUNCTIONS can be called directly from the SQL.
• PL/SQL can run without the involvement of human.
• Programs can run on the different Operating Systems.
• PL/SQL SUPPORTS Loops, CONDITIONS, and OOPS concepts.

The TRUNCATE STATEMENT removes all the RECORDS from the table in the ORACLE database. If once the TRUNCATE statement truncate the table then the data cannot be recovered back.

Syntax:- TRUNCATE TABLE table_name

Here are some of the features of the ORACLE:-

• Backup and RECOVERY of Data:-ORACLE provides Flashback technology which LEADS to efficient recovery of data.
• Portable:-The ORACLE database has been ported to many platforms, and as a result, the applications on Oracle are safe when the OS is changed.
• Speed:-Speed of the ORACLE database is good
• Multiple Database Management:-ORACLE manages various databases at the same TIME. The user can quickly move at a place where data is actually stored from the node to node in a network
• Efficient Data Integrity:-ORACLE uses the integrity constraints due to which invalid data entry is restricted to be entered into the database tables.
• Provides Cursor Support:-With the help of cursor, programming becomes easy due to the row-to-row processing.

ORACLE was developed by Lawrence Ellison and his co-workers BOB Miner and ED Oates

in the year 1977. The first version ORACLEv2 was released in the year 1979 which was the

first AVAILABLE SQL based RDBMS.

The LATEST version of Oracle DATABASE is 18c. This version got RELEASED on 16TH February 2018.

Oracle is fundamentally a relational database management system. By using ORACLE, the user can directly access the objects through the Structured QUERY Language(SQL). Oracle is DESIGNED to support multiple data models. Oracle runs on Windows, UNIX, Linux, and Mac OS.Oracle is written in Assembly language, C & C++.

Because of the FOLLOWING reasons Oracle is the most used database software.

• Flashback Technology:-Recovery of the data is done efficiently
• ACID tool:-maintains the integrity of the information
• Oracle can be used for small business applications as well as large business applications.

Here is the list of Oracle12c new features:-

• Pluggable DATABASE:-This feature has CHANGED the ORACLEdatabase ARCHITECTURE. In this, the Metadata is stored in the container database, and the user data is stored in the Pluggable Database.
• Data Redaction:-This is the essential feature of 12C.Data Redaction basically means masking of the data.
• RMAN command:-RMAN (Recovery Manager)command is used to restore a particular table which used to be a hard job before.
• Multiple indexes:-Now, the column can be in more than one INDEX. For example -Column can be included in the B-tree index as well as a Bit Map index but only one used at a time.