SQL SELECT Query

The SQL SELECT statement retrieves data from a table. List the columns you need after SELECT and the table after FROM.

SELECT id, name, class, mark
FROM student;

This returns the four selected columns for every row in the student table.

SQL SELECT Syntax Top ↑

SELECT column1, column2
FROM table_name;

Use a comma to separate multiple column names. The semicolon ends the SQL statement in tools and scripts that support multiple statements.

For example:

SELECT name, class
FROM student;

Select Only the Columns You Need Top ↑

When an application needs only a few fields, name those columns explicitly:

SELECT id, name, mark
FROM student;

This is usually clearer than retrieving every column. It also avoids transferring columns the application does not use.

Using SELECT * Top ↑

An asterisk means all columns:

SELECT *
FROM student;

SELECT * is convenient while exploring a small table or when every column is genuinely needed. In application code, explicit column lists are often preferable because the required result structure remains clear even if the table later gains more columns.

Column Aliases and Expressions Top ↑

Use AS to give a result column a readable alias:

SELECT name AS student_name, mark AS score
FROM student;

A SELECT list can also contain expressions and functions. For example, CONCAT() can combine values:

SELECT CONCAT(name, ' - ', class) AS student_details
FROM student;

The alias changes the result-column label; it does not rename the column in the table.

Return Unique Values with DISTINCT Top ↑

To return each class value once:

SELECT DISTINCT class
FROM student;

DISTINCT applies to the selected result values. Multiple selected columns make each unique combination significant.

Filter Rows with WHERE Top ↑

SELECT returns all matching rows unless a condition restricts them. Use WHERE to filter the rows:

SELECT id, name, class, mark
FROM student
WHERE class = 'Four';

Other dedicated filtering tutorials cover LIKE, BETWEEN, IN, AND/OR and NULL conditions.

Sort and Limit SELECT Results Top ↑

Use ORDER BY when the order matters:

SELECT id, name, mark
FROM student
ORDER BY mark DESC, id ASC;

Here the highest marks appear first. The additional id ASC provides a consistent tie-breaker when students have the same mark.

Use LIMIT in MySQL to return only part of the result:

SELECT id, name, mark
FROM student
ORDER BY mark DESC, id ASC
LIMIT 3;

For pagination, LIMIT is normally combined with a deterministic ORDER BY so moving between pages does not depend on an unspecified row order.

Common SELECT Clause Order Top ↑

A more complete SELECT query can contain several clauses. They are written in this order:

SELECT column_list
FROM table_name
WHERE condition
GROUP BY column_list
HAVING group_condition
ORDER BY column_list
LIMIT row_count;

Not every SELECT query needs every clause. Use only the parts required by the result.

Display SELECT Results with PHP PDO Top ↑

After creating a PDO database connection, a fixed SELECT query can be executed with query(). Select only the columns needed by the output.

<?php
require 'config.php';

$sql="SELECT id,name,class,mark
      FROM student
      ORDER BY id
      LIMIT 4";

$stmt=$dbo->query($sql);

echo '<table>';
echo '<tr><th>ID</th><th>Name</th><th>Class</th><th>Mark</th></tr>';

while($row=$stmt->fetch(PDO::FETCH_ASSOC)){
    $id=(int)$row['id'];
    $name=htmlspecialchars((string)$row['name'],ENT_QUOTES,'Windows-1252');
    $class=htmlspecialchars((string)$row['class'],ENT_QUOTES,'Windows-1252');
    $mark=(int)$row['mark'];

    echo "<tr><td>$id</td><td>$name</td><td>$class</td><td>$mark</td></tr>";
}

echo '</table>';

If the query includes external values such as a user-selected class or ID, use a PDO prepared statement instead of concatenating the value into SQL.

SQL SELECT Video Tutorials Top ↑

Common SQL SELECT Problems Top ↑

Assuming Rows Have a Default Order Top ↑

A table has no guaranteed presentation order. Add ORDER BY whenever the result must be consistently sorted.

Using SELECT * Everywhere Top ↑

SELECT * is useful for exploration, but application queries are often clearer and more efficient when they request only the required columns.

Writing Clauses in the Wrong Order Top ↑

For example, WHERE is written before ORDER BY and LIMIT. Follow the normal SELECT clause order shown above.

Using = NULL in a WHERE Condition Top ↑

NULL is tested with IS NULL or IS NOT NULL, not ordinary equality. See the SQL NULL tutorial.

Building SQL with Untrusted Application Input Top ↑

SELECT syntax does not protect an application from SQL injection. When values come from a form, URL or other external source, validate them and use prepared statements in the application layer.

Selecting More Data Than the Page Needs Top ↑

Large tables and large columns can make unnecessary result sets expensive. Select the required columns and apply appropriate filtering or limits for the task.

Related SQL SELECT Tutorials Top ↑

Frequently Asked Questions Top ↑

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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