Sql And Plsql Interview Questions And Answers
Comprehensive SQL and PL/SQL Interview Questions and Answers
Sql And Plsql Interview Questions And Answers
In a SQL interview, expect to be asked questions about querying databases using SELECT statements, managing data with INSERT, UPDATE, DELETE, joining tables, aggregating data with GROUP BY, and filtering results with WHERE and HAVING clauses. PL/SQL interview questions typically focus on procedural language constructs like variables, loops, conditional statements, cursors, and exception handling in addition to understanding packages, functions, and triggers. Be prepared to showcase your SQL skills in manipulating data and your PL/SQL expertise in developing stored procedures and functions.
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1 - What is SQL and PL/SQL?
SQL stands for Structured Query Language, which is a standard language for accessing and manipulating databases. PL/SQL stands for Procedural Language/Structured Query Language, and it is an extension of SQL that allows developers to write procedural logic within SQL statements.
2) What are the differences between SQL and PL/SQL?
SQL statements are used to perform operations on the database, such as querying or updating data. PL/SQL, on the other hand, allows us to write procedural code like loops, conditions, and exception handling within SQL statements.
3) What are the basic data types in PL/SQL?
Basic data types in PL/SQL include VARCHAR2, NUMBER, DATE, CHAR, BOOLEAN, etc. VARCHAR2 is used for storing variable length character strings, NUMBER is used for numeric values, DATE is used for date and time values, CHAR is used for fixed length character strings, and BOOLEAN is a boolean data type that can have values TRUE, FALSE, or NULL.
4) What is a cursor in PL/SQL?
A cursor in PL/SQL is a pointer that allows us to process individual rows returned by a query. It provides a way to iterate over the result set and perform operations on each row.
5) What is an exception in PL/SQL?
Exceptions in PL/SQL are errors that occur during the execution of a block of code. We can handle exceptions using the EXCEPTION block in PL/SQL, which allows us to take appropriate actions when an error occurs.
6) How do you declare variables in PL/SQL?
Variables in PL/SQL are declared using the DECLARE keyword followed by the variable name, data type, and optional default value. For example, DECLARE
v_name VARCHAR2(50) := ‘John’;
7) How do you write a PL/SQL block?
A PL/SQL block typically starts with the DECLARE section where variables are declared, followed by the BEGIN section where the actual code logic is written, and ends with the EXCEPTION section to handle any errors that occur. For example,
DECLARE
v_num NUMBER := 10;
BEGIN
IF v_num > 5 THEN
DBMS_OUTPUT.PUT_LINE('Number is greater than 5');
END IF;
END;
8) Explain the difference between TRUNCATE and DELETE in SQL.
TRUNCATE is a DDL statement that removes all rows from a table, but it does not log individual row deletions. DELETE is a DML statement that removes specific rows from a table based on a condition, and it logs each row deleted.
9) What is a trigger in PL/SQL?
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A trigger in PL/SQL is a database object that automatically executes in response to certain events on a particular table or view. Triggers can be used to enforce business rules, audit changes, or maintain data integrity.
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