JSTL (JavaServer Pages Standard Tag Library) SQL tags allow you to execute SQL queries and manipulate the resulting data within JSP (JavaServer Pages) pages. Here's an example of using JSTL SQL tag to execute a SELECT query:

<%@ taglib uri="http://java.sun.com/jsp/jstl/sql" prefix="sql" %>
<sql:setDataSource
  var="dataSource"
  driver="com.mysql.jdbc.Driver"
  url="jdbc:mysql://localhost/test"
  user="root"
  password="password"/>

<sql:query var="result" dataSource="${dataSource}">
  SELECT * FROM customers;
</sql:query>

<c:forEach var="row" items="${result.rows}">
  <c:out value="${row.id}"/><br/>
  <c:out value="${row.name}"/><br/>
  <c:out value="${row.email}"/><br/>
</c:forEach>

In the above example, we first define the data source using the sql:setDataSource tag. This specifies the driver, URL, username, and password for connecting to the database. We then use the sql:query tag to execute a SELECT query and store the results in a variable called result. Finally, we use the c:forEach tag to iterate over the rows in result and display the values of the id, name, and email columns.

Note that JSTL SQL tags have been deprecated since JSTL 1.2, so it is recommended to use a different method for database access, such as JDBC or an ORM (Object-Relational Mapping) framework like Hibernate.