SQL Interview Questions and Answers
SQL, or Structured Query Language, is a language that is used to interact or communicate with a database. This language assists in performing tasks like retrieval, insertion, updating, and deletion of data from databases. This information is commonly asked in SQL interview questions. An ANSI (American National Standards Institute) standard, SQL helps developers execute queries, insert records in tables, update records, create databases, create tables, or delete tables.
No doubt other programming languages such as ASP, PHP, and ColdFusion helped in making the Internet very dynamic, but SQL has revolutionized how users interact with websites in general. Any reputed webpage that allows the user to provide content uses SQL.
Most Frequently Asked SQL Interview Questions
TRUNCATE
- It removes all rows from a table.
- It does not require a WHERE clause.
- Truncate cannot be used with indexed views.
- It is performance wise faster.
DROP
- It removes a table from the database.
- All table's rows, indexes, and privileges will also be removed when we used this command.
- The operation cannot be rolled back.
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SELECT * FROM employee WHERE name LIKE 'um%';
It is the source of a rowset to be operated upon in a DML statement. These clauses are very common which is used with Select statement, Update statement and Delete statement.
SQL provides with the following clauses that are given below:
- WHERE
- GROUP BY
- HAVING
- ORDER BY etc
count(): It returns the number of rows in a table satisfying the condition specified in the WHERE clause. It would return 0 if there were no matching conditions.
Syntax:
SELECT COUNT(*) FROM category WHERE 'status' = 1;
distinct(): It is used to return only different values. In a table, a column often contains many duplicate values, and sometimes we want to list the different values. It can be used with aggregates functions.
Syntax:
SELECT DISTINCT class FROM College ORDER BY department
This information was frequently asked during SQL interview questions for testers.
It is a set of precompiled SQL statements that are used to perform a particular task. A procedure has a name, a parameter list, and SQL statement, etc. It will help in reduce network traffic and increase the performance.
CREATE PROCEDURE simple_function
AS
SELECT first_name, last_name
FROM employee;
EXEC simple_function;