The SELECT statement in SQL is used to retrieve data from a database table. To further refine your query and retrieve more specific results, you can use the WHERE clause. The WHERE clause allows you to filter data based on specified conditions.

Syntax

The basic syntax of the SELECT statement with the WHERE clause is as follows:

SELECT column1, column2, ...
FROM table_name
WHERE condition;

Here, column1, column2, ... represents the columns that you want to retrieve from the table, table_name is the name of the table from which data is retrieved, and condition is the filter criteria.

Examples

Example 1: Retrieving specific rows from a table

Suppose we have a table named users with columns id, name, age, and country. To retrieve all rows where the age is greater than 30, the SQL query would be:

SELECT * FROM users
WHERE age > 30;

This query will return all rows from the users table where the age column has a value greater than 30.

Example 2: Using multiple conditions

In some cases, you may want to use multiple conditions to filter data. For instance, let’s say you want to retrieve all rows where the age is greater than 30 and the country is ‘USA’. The SQL query would be:

SELECT * FROM users
WHERE age > 30 AND country = 'USA';

This query will return all rows where the age is greater than 30 and the country is ‘USA’.

Example 3: Using wildcard characters

You can also use wildcard characters like % and _ in the WHERE clause to perform pattern matching. For instance, to retrieve all rows where the name starts with ‘J’, the SQL query would be:

SELECT * FROM users
WHERE name LIKE 'J%';

This query will return all rows where the name column starts with the letter ‘J’.

Conclusion

The WHERE clause in the SQL SELECT statement allows you to filter and retrieve specific data from a database table based on the specified conditions. By using the WHERE clause effectively, you can narrow down the results and extract the data you need for your application.

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