Oracle SQL Interview Preparation Guide

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SQL*PLUS is a command line tool where as SQL and PL/SQL language interface and reporting tool. Its a command line tool that allows user to type SQL commands to be executed directly against an Oracle database. SQL is a language used to query the relational database(DML,DCL,DDL). SQL*PLUS commands are used to format query result, Set options, Edit SQL commands and PL/SQL.

Oracle uses work area to execute SQL statements and store processing information PL/SQL construct called a cursor lets you name a work area and access its stored information A cursor is a mechanism used to fetch more than one row in a Pl/SQl block.

Cursor is a variable.
it is similar to a 2D array .
used for processing multiple rows.
used for storing data temporarily.

Self join-Its a join foreign key of a table references the same table. Outer Join--Its a join condition used where One can query all the rows of one of the tables in the join condition even though they don't satisfy the join condition.
Equi-join--Its a join condition that retrieves rows from one or more tables in which one or more columns in one table are equal to one or more columns in the second table.

-Data base trigger(DBT) fires when a DML operation is performed on a data base table. Form trigger(FT) Fires when user presses a key or navigates between fields on the screen
-Can be row level or statement level No distinction between row level and statement level.
-Can manipulate data stored in Oracle tables via SQL Can manipulate data in Oracle tables as well as variables in forms.
-Can be fired from any session executing the triggering DML statements. Can be fired only from the form that define the trigger.
-Can cause other database triggers to fire.Can cause other database triggers to fire, but not other form triggers.

yes you can assign default value to an actual parameter.. If the actual parameter holds NULL value then the DEFAULT Value will be assigned.

In PL/SQL 2.2 cursor variables cannot be declared in a package.This is because the storage for a cursor variable has to be allocated using Pro*C or OCI with version 2.2, the only means of passing a cursor variable to a PL/SQL block is via bind variable or a procedure parameter.

SUBSTR returns a specified portion of a string eg SUBSTR('BCDEF',4) output BCDE
INSTR provides character position in which a pattern is found in a string. eg INSTR('ABC-DC-F','-',2) output 7 (2nd occurence of '-')

UTL_FILE is a package that adds the ability to read and write to operating system files. Procedures associated with it are FCLOSE, FCLOSE_ALL and 5 procedures to
output data to a file PUT, PUT_LINE, NEW_LINE, PUTF, FFLUSH.PUT, FFLUSH.PUT_LINE,FFLUSH.NEW_LINE. Functions associated with it are FOPEN, ISOPEN.

EXISTS is faster than IN
Because exists returns Boolean value whereas IN returns only value.

SELECT DISTINCT (a.sal) FROM EMP A WHERE &N = (SELECT COUNT (DISTINCT (b.sal)) FROM EMP B WHERE a.sal<=b.sal);
For Eg:-
Enter value for n: 2
SAL
---------
3700

The return type for a cursor must be a record type.It can be declared explicitly as a user-defined or %ROWTYPE can be used. eg TYPE t_studentsref IS REF CURSOR
RETURN students%ROWTYPE

select level, min('col_name') from my_table where level = '&n' connect by prior ('col_name') <
'col_name')
group by level;
Example:
Given a table called emp with the following columns:
-- id number
-- name varchar2(20)
-- sal number
--
-- For the second lowest salary:
-- select level, min(sal) from emp
-- where level=2
-- connect by prior sal < sal
-- group by level

select max(sal)"nth min sal" from(select distinct sal from emp order by sal) where rownum<=&N

Oracle does not allow a user to specifically locate tables, since that is a part of the function of the RDBMS. However, for the purpose of increasing performance, oracle allows a developer to create a CLUSTER. A CLUSTER provides a means for storing data from different tables together for faster retrieval than if the table placement were left to the RDBMS.

it's a temporary and logical memory allocation where we can put several tables.

Functions are named PL/SQL blocks that return a value and can be called with arguments procedure a named block that can be called with parameter. A procedure all is a PL/SQL statement by itself, while a Function call is called as part of an expression.

Function and Procedure both are PL/SQL blocks, main difference between function and procedure is -
Function has to return some value using return clause whereas procedure may or may not return any value( no out parameter).

We can use functions in SQL query but can't use procedure.

the following data types are used to store graphics or binary data
1)long raw
2)binary large object(BLOB)
3)binary file(BFILE)

PL/SQL declares a cursor implicitly for all SQL data manipulation statements, including quries that return only one row. However,queries that return more than one row you must declare an explicit cursor or use a cursor FOR loop. Explicit cursor is a cursor in which the cursor name is explicitly assigned to a SELECT statement via the CURSOR...IS statement. An implicit cursor is used for all SQL
statements Declare, Open, Fetch, Close. An explicit cursors are used to process multirow SELECT statements An implicit cursor is used to process INSERT, UPDATE, DELETE and single row SELECT. .INTO statements.

The implicit cursor is used to process INSERT, UPDATE,
DELETE, and SELECT INTO statements. During the processing of
an implicit cursor,Oracle automatically performs the OPEN,
FETCH, and CLOSE operations.

Where as in explicit cursors,the process of its working is
done in 4 steps namely DECLARE a cursor,OPEN a cursor,
FETCH from cursor and CLOSE a
cursor.

IMPLICT CURSOR:- Automatically porvide by oracle which
perform DML statements. queries returns only one row.

EXPLICT CURSOR:- Defined by user. queries returns more
than rows.

Explicit Cursor:-We are not able to Handle NO_DATA_FOUND
Exception.

Implicit Cursor:-We are able to Handle NO_DATA_FOUND
Exception.