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
It is a function that takes one or more values but returns a single value. It is based on user input and returns a single value.
- UCASE()
- LCASE()
- MID()
- LEN()
- ROUND()
- NOW()
- FORMAT()
The aggregate function performs a calculation on a set of values, and it returns a single value as output. It ignores NULL values when it performs calculation except for the COUNT function.
SQL provides many aggregate functions that are listed below.
- AVG()
- COUNT()
- SUM()
- MIN()
- MAX() etc
UPDATE `table_name` SET new_field=old_field
There are many advantages of SQL, and some of them are mentioned below:
- No coding needed: It is easy to manage without any need to write the substantial amount of code
- Well defined standards: Long established are used by the SQL databases that are being used by ISO and ANSI.
- Portability: We can use this program in PCs, servers, laptops and mobile phones.
- Interactive Language
- Multiple data views
It was initially developed in the early 1970s at IBM by Donald D. Chamberlin and Raymond F. Boyce.
It is a collection of data that is organized to be easily accessed, managed and updated. It is distributed into rows, columns, and tables. It's indexed to make it easier to find related information.
Table: It is a collection of related data that consists of rows and columns. It has a specified number of columns but can have any number of rows.
Field: It is a column in a table that is designed to maintain specific information about all records in the table.
It is a set of one or more than one fields or columns of a table that uniquely identify a record in the table. It is little like a primary key, but it can accept only one null value.
It is a collection of fields in one table that uniquely identifies a row of another table. In simple words, the foreign key is defined in a second table, but it refers to the primary key/unique key in the first table.
SELECT CURDATE();