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Questions for SQL Interviews

1. What exactly is a database?

A database is a digitally stored and retrieved collection of data from a remote or local computer system. Databases can be large and sophisticated, and they are built using pre-determined design and modeling methodologies.

2. What is a database management system (DBMS)

The term DBMS refers to a database management system. A database management system (DBMS) is a piece of software that allows you to create, retrieve, update, and manage databases. By acting as an interface between the database and its end-users or application software, it ensures that our data is consistent, organized, and easily available.

3. What is a relational database management system (RDBMS)? What distinguishes it from a database management system (DBMS)?

Relational Database Management System (RDBMS) is an acronym for Relational Database Management System. The main distinction between RDBMS and DBMS is that RDBMS stores data in the form of a collection of tables, with relations specified between the tables' common fields. RDBMS is the foundation of most modern database management systems, including MySQL, Microsoft SQL Server, Oracle, IBM DB2, and Amazon Redshift.

4. What exactly is SQL?

Structured Query Language (SQL) is an acronym for Structured Query Language. It's the industry standard for database management systems that use relational databases. It's notably handy for dealing with structured data made up of entities (variables) and relationships between them. Here check the sql server interview questions tips and information.

5. How do SQL and MySQL differ from one another?

SQL is a programming language that is used to retrieve and manipulate organized databases. MySQL, on the other hand, is a relational database management system used to manage SQL databases, similar to SQL Server, Oracle, or IBM DB2.

6. What are the differences between tables and fields?

A table is a collection of data that is structured into rows and columns. Vertical columns and horizontal rows are the two types of columns and rows, respectively. A table's columns are known as fields, while the rows are known as records.

7. What are SQL Constraints?

Constraints are used to define the rules that govern the table's data. It can be used on a single or multiple fields in a SQL table when the table is created or after it has been created using the ALTER TABLE command. The following are the limitations:

  • NOT NULL - Prevents the insertion of a NULL value into a column.
  • CHECK - Checks that all values in a field meet a set of criteria.
  • DEFAULT - If no value has been specified for the field, it will be assigned a default value.
  • UNIQUE - Ensures that the field's values are unique.
  • INDEX - Indexes a field to allow for speedier record retrieval.
  • PRIMARY KEY - Identifies each record in a database in a unique way.
  • FOREIGN KEY - Protects a record in another table's referential integrity.

8. What is the definition of a primary key?

Each row in a table is uniquely identified by the PRIMARY KEY constraint. It contains an implied NOT NULL constraint and must include UNIQUE data.

In SQL, a table can only have one and only one primary key, which can be made up of single or multiple fields (columns).

9. What does it mean to have a UNIQUE constraint?

A UNIQUE constraint guarantees that each value in a column is unique. This ensures that the column(s) are unique and that each row can be identified separately. Unlike primary keys, each table can have several unique constraints. UNIQUE has a code syntax that is very similar to PRIMARY KEY and can be used interchangeably.

10. What is a Foreign Key, exactly?

A FOREIGN KEY is a single field or a group of fields in a table that refers to the PRIMARY KEY in another table. The foreign key constraint assures that the relationship between two tables is referentially sound.

The child table is the one with the foreign key constraint, while the referred or parent table is the one with the candidate key.

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