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Computer Science Data Query Language (DQL) command DQL is used to fetch the data from the
database. It uses only one command, which is SELECT. Its syntax is SELECT
column1, column2, ...FROM table_name; Example: If you want to retrieve the first
name and middle name only from the student-registration table, the query is such
that: SELECT FirstName, MiddleName FROM student_registration OUTPUT (see
FOR ONLINE READING ONLY
Figure 8.24):

Mwakatope Mkinga
Mkinga Mwakalinga

Mwakalinga Mwakatope

Figure 8.24: The output of the SELECT query

Data Query Language (DQL) commands
Data Query Language (DQL) commands are a type of SQL commands primarily
used for querying and retrieving data from databases. The main DQL command is
‘SELECT’, which fetches data from one or more tables. This command allows users
to specify which columns to retrieve, filter results using conditions, join tables,
and sort the output. DQL is fundamental for accessing and analyzing data stored in
relational databases. Example of a Data Query Language (DQL) command in SQL:
SELECT name, age, email
FROM users
WHERE age > 45

ORDER BY name ASC;
This query retrieves the name, age, and email columns from the users table where
the age is greater than 45, and it orders the results by name in ascending (ASC) order.
The primary DQL command in SQL is the SELECT statement. However, SQL uses
other statements for querying data indirectly through the SELECT statement, such
as using operators and clauses.

Common operators and clauses used with SELECT command
These functions are such as ‘JOIN’, ‘WHERE’, ‘ORDER BY’, ‘GROUP BY’,
‘HAVING’, and ‘UNION’, ‘EXISTS’, ‘IN’, ‘BETWEEN’, and ‘LIKE’

(a) SELECT
This ‘SELECT’ command retrieves data from a database. For example,
SELECT * FROM employees;

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for Advanced Secondary Schools

Computer Science Form 5.indd 472 23/07/2024 12:35