Relational Database Management System (RDBMS) is one of the most extensively used database management systems to date, and so SQL skills are required for the majority of employment jobs. We will introduce you to the most often asked SQL interview questions in this post (Structured Query Language). This page is an excellent resource for learning everything about SQL, Oracle, MS SQL Server, and MySQL databases. Our post on the Top 15 SQL Interview Questions is a one-stop source for interview preparation.
MySQL is one of the most extensively utilized open-source database management systems (database management systems). MySQL is a simple to use, dependable, and quick database management system. A database management system that runs on both embedded and client-server platforms.
To begin, MySQL is an open-source database management system. Second, it is extensively accepted, which means that a substantial amount of code is already accessible. Even whole developed systems are available for reference in prospective projects. MySQL utilizes relational databases, which results in systematic storage rather than a large jumble of disorganized data. Finally, as previously said, MySQL is a fast and robust database management system.
This is a critical MySQL interview question to know. Let's dive into the answer:
MySQL organizes data into logical tables. Tables may be considered as MySQL's primary storage structure. As a result, tables are sometimes referred to as storage engines. MySQL supports the following storage engines:
This requires an ALTER TABLE query. Simply specify the column and its definition once it has been called. As follows:
ALTER TABLE cars ADD COLUMN engine VARCHAR(80) AFTER color;
Two tables are connected using a foreign key. A FOREIGN KEY is a field (or cluster of fields) in one table that refers to another table's PRIMARY KEY. The FOREIGN KEY constraint is utilized to prevent operations that might result in the crushing of joins between tables.
To create a foreign key, it is necessary to indicate it during the table creation process. The FOREIGN KEY query may be used to allocate it. As follows:
EXTERNAL KEY (Any ID) REFERENCES Table to reference(Any ID)
MySQL Workbench is a unified visual toolkit for database designers, modelers, and DBAs. MySQL Workbench is a collection of administrative tools for data modeling, SQL, and server configuration. Simply stated, MySQL workbench enables users to interact with the database management system through a graphical user interface.
It is possible to do this in two ways. One is to use phpMyAdmin, while the other is to utilize MySQL's command line interface. The latter may be accomplished by using the mysqldump command. It goes as follows:
· mysqldump -u username -p databasename > dbsample.sql
To import a database into MySQL, all that is necessary is a sign change using a MySQL command. The command is as follows:
· mysql -u username -p databasename < dbsample.sql
Now, you may easily drop a column by using the ALTER TABLE command followed by the DROP command. It goes as follows:
ALTER TABLE table_name DROP column name;
To drop a row, it is necessary to first create an identity for the row. Once that is convenient, combine the DELETE command with the conditional WHERE command. As follows:
DELETE FROM cars WHERE carID = 3;
Join is used to connect two or more tables together using the values of a common column in both tables. There are four primary kinds of joins:
1. Inner Join - An inner join is one that makes use of a join predicate, which is a condition that is employed to perform the join. The following is the syntax:
SELECT something FROM tablename INNER JOIN another table ON condition;
2. Left Join — Like the right join, the left join needs a join condition. The left join selects data starting with the left table. The left table compares each item in the left table to each entry in the right table. The following is the syntax:
SELECT something FROM tablename LEFT JOIN another table ON condition;
3. Right Join — Contrary to left join, but with one distinction in the query: the name of the join. Here, attention should be made with the arrangement of the tables. The following is the syntax:
SELECT something FROM tablename LEFT JOIN another table ON condition;
4. Cross Join - A cross join is one that does not need a join condition. It creates a cartesian representation of the rows in both tables. The following is the syntax:
SELECT something FROM tablename CROSS JOIN another table;
Self-join is also available when working with a single table.
It is a frequently asked MySQL interview question. Interviewers are interested in determining if the applicant grasps the fundamentals and can connect one of the main ideas.
Yes, it is possible to delete a table's primary key. Once again, the command to use is ALTER TABLE followed by DROP. It goes as follows:
ALTER TABLE table_name DROP PRIMARY KEY;
Procedures (or stored procedures) are embedded subprograms in the database, similar to how they are in a normal language. A stored procedure is composed of the following elements: a name, SQL statement(s), and arguments. As with prepared statements, it makes use of MySQL's caching and so saves time and memory.
In MySQL, a trigger is a database entity that is connected with a table. It is triggered when a particular action occurs.
A trigger might be called after or before an event occurs. It is applicable to INSERT, DELETE, and UPDATE operations. It defines the triggers using the appropriate syntax. For instance, BEFORE INSERT, AFTER DELETE, and so on.
To put it simply, the user may be added by issuing the CREATE command and providing the required credentials. Log in to the MySQL account first, and then execute the syntax. As follows:
CREATE USER ‘testuser’ IDENTIFIED BY ‘sample password’;
Permissions may be provided to users using the following commands:
GRANT SELECT ON * . * TO ‘testuser’;
The primary distinction is that MySQL utilizes a single-model database. That is, it is limited to a single base structure, while Oracle is a multi-model database. This implies that it is capable of supporting a variety of data models, including graphs, documents, and key-value.
Another critical distinction is that Oracle's support is not free for industrial solutions. Whereas MySQL is an open-source project.
Now, this is one of the MySQL interview questions that should be well grasped. Because it is closely related to industry standards and the company's objectives.
Both of these constructs define a string. The fundamental distinction is that CHAR has a set length, but VARCHAR has a variable length. For instance, if CHAR(5) is specified, it requires precisely five characters. When VARCHAR(5) is defined, it can contain no more than five characters. VARCHAR may be stated to be more efficient in terms of memory utilization due to its ability to do dynamic memory allocations.
Once you go through the above questions and answers, you have a good chance of cracking most MySQL interviews.