Top 50 Sql Query Interview Questions You Must Practice In 2023

By Author: Datacademy.ai
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SQL Query Interview Questions

1. What is SQL and why is it used?
SQL (Structured Query Language) is a programming language used to communicate with and manipulate databases. It is used to create, alter, and query relational databases, which store data in tables consisting of rows and columns.

2. What are the different types of SQL commands?
There are several types of SQL commands, including:

Data Definition Language (DDL) commands: These commands are used to define the database structure or schema. Examples include CREATE, ALTER, and DROP.
Data Manipulation Language (DML) commands: These commands are used to manipulate data within the database. Examples include SELECT, INSERT, UPDATE, and DELETE.
Data Control Language (DCL) commands: These commands are used to control access to the database. Examples include GRANT and REVOKE.
3. How do you select all columns from a table?
To select all columns from a table, use the following syntax:

SELECT * FROM table_name;
4. How do you select a specific column from a table?
To select a specific column from a table, ...
... use the following syntax:

SELECT column_name FROM table_name;
5. How do you select distinct values from a column?
To select distinct values from a column, use the DISTINCT keyword in your SELECT statement:

SELECT DISTINCT column_name FROM table_name;
6. How do you count the number of rows in a table?
To count the number of rows in a table, use the COUNT function:

SELECT COUNT(*) FROM table_name;
7. How do you create a new table in a database?
To create a new table in a database, use the CREATE TABLE statement:

CREATE TABLE table_name (
column_1 datatype constraint,
column_2 datatype constraint,
...
);
8. How do you add a column to an existing table?
To add a column to an existing table, use the ALTER TABLE and ADD COLUMN statements:

ALTER TABLE table_name
ADD COLUMN column_name datatype constraint;
9. How do you update data in a table?
To update data in a table, use the UPDATE and SET statements:

UPDATE table_name
SET column_name = new_value
WHERE condition;

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