constraint.html

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            <h1>SQL Constraints</h1>

            <p>SQL constraints are used to specify rules for data in a table.</p>
            <p>Constraints can be specified when the table is created with the <strong>CREATE TABLE</strong> statement,
                or after the table is created with the <strong>ALTER TABLE</strong> statement.</p>

            <h2>CREATE Table with Constraints Syntax</h2>
            <pre><code class="language-sql">CREATE TABLE table_name (
    column1 datatype constraint,
    column2 datatype constraint,
    column3 datatype constraint,
    ....
);</code></pre>

            <h2>About SQL Constraints</h2>
            <p>Constraints are used to limit the type of data that can go into a table. This ensures the accuracy and
                reliability of the data.
                If a constraint is violated, the action is aborted.</p>
            <p>Constraints can be <strong>column level</strong> (applies to a single column) or <strong>table
                    level</strong> (applies to the whole table).</p>

            <h2>Common SQL Constraints</h2>
            <ul>
                <li><strong>NOT NULL</strong> - Ensures that a column cannot have a NULL value</li>
                <li><strong>UNIQUE</strong> - Ensures that all values in a column are different</li>
                <li><strong>PRIMARY KEY</strong> - A combination of NOT NULL and UNIQUE. Uniquely identifies each row in
                    a table</li>
                <li><strong>FOREIGN KEY</strong> - Prevents actions that would destroy links between tables</li>
                <li><strong>CHECK</strong> - Ensures that the values in a column satisfy a specific condition</li>
                <li><strong>DEFAULT</strong> - Sets a default value for a column if no value is specified</li>
            </ul>
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