List of 90 SQL Server Interview Questions and Answers
Q #1) What is SQL?
Answer: Structured Query Language SQL is a database tool that is used to create and access the database to support software applications.
Q #2) What are tables in SQL?
Answer: The table is a collection of records and information in a single view.
Q #3) What are the different types of statements supported by SQL?
Answer:
statements supported by SQL
There are 3 types of SQL statements:
a) DDL (Data Definition Language): It is used to define the database structure such as tables. It includes three statements such as CREATE, ALTER, and DROP.
Some of the DDL Commands are listed below:
CREATE: It is used for creating the table.
CREATE TABLE table_name
column_name1 data_type(size),
column_name2 data_type(size),
column_name3 data_type(size),
ALTER: The ALTER table is used for modifying the existing table object in the database.
ALTER TABLE table_name
ADD column_name datatype
OR
ALTER TABLE table_name
DROP COLUMN column_name
b) DML (Data Manipulation Language): These statements are used to manipulate the data in records. Commonly used DML statements are INSERT, UPDATE, and DELETE.
The SELECT statement is used as a partial DML statement, used to select all or relevant records in the table.
c) DCL (Data Control Language): These statements are used to set privileges such as GRANT and REVOKE database access permission to the specific user.
Q #4) How do we use the DISTINCT statement? What is its use?
Answer: The DISTINCT statement is used with the SELECT statement. If the record contains duplicate values then the DISTINCT statement is used to select different values among duplicate records.
Syntax:
SELECT DISTINCT column_name(s)
FROM table_name;
Q #5) What are different Clauses used in SQL?
Answer:
Clauses used in SQL
WHERE Clause: This clause is used to define the condition, extract and display only those records which fulfill the given condition.
Syntax:
SELECT column_name(s)
FROM table_name
WHERE condition;
GROUP BY Clause: It is used with a SELECT statement to group the result of the executed query using the value specified in it. It matches the value with the column name in tables and groups the end result accordingly.
Syntax:
SELECT column_name(s)
FROM table_name
GROUP BY column_name;
HAVING clause: This clause is used in association with the GROUP BY clause. It is applied to each group of results or the entire result as a single group. It is much similar to the WHERE clause but the only difference is you cannot use it without the GROUP BY clause
Syntax:
SELECT column_name(s)
FROM table_name
GROUP BY column_name
HAVING condition;
ORDER BY clause: This clause is used to define the order of the query output either in ascending (ASC) or descending (DESC). Ascending (ASC) is set as the default one but descending (DESC) is set explicitly.
Syntax:
SELECT column_name(s)
FROM table_name
WHERE condition
ORDER BY column_name ASC|DESC;
USING clause: USING clause comes in use while working with SQL JOIN. It is used to check equality based on columns when tables are joined. It can be used instead of the ON clause in JOIN.
Syntax:
SELECT column_name(s)
FROM table_name
JOIN table_name
USING (column_name);
