SQL Syntax

Last modified on: December 2, 2024

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<h3><strong>SQL Syntax: A Comprehensive Guide</strong></h3>
<h4><strong>What is SQL Syntax?</strong></h4>
<p>SQL syntax refers to the rules and structure used to write SQL statements for interacting with relational databases. It defines how commands, clauses, and keywords should be arranged to perform database operations like querying, updating, and managing data.</p>
<p>SQL syntax is standardized and relatively easy to learn, making it an essential skill for developers and data analysts.</p>
<hr />
<h4><strong>Key Components of SQL Syntax</strong></h4>
<ol>
<li><strong>Keywords</strong>: Reserved words like <code>SELECT</code>, <code>FROM</code>, <code>WHERE</code>, <code>INSERT</code>, and <code>UPDATE</code> that define operations.</li>
<li><strong>Clauses</strong>: Parts of an SQL statement, such as <code>WHERE</code>, <code>GROUP BY</code>, and <code>ORDER BY</code>, that refine queries.</li>
<li><strong>Expressions</strong>: Combinations of values, operators, and functions used to perform calculations or comparisons.</li>
<li><strong>Statements</strong>: Complete commands like <code>CREATE TABLE</code> or <code>SELECT</code> that perform tasks.</li>
</ol>
<hr />
<h4><strong>SQL Syntax Rules</strong></h4>
<ol>
<li><strong>Case Sensitivity</strong>:
<ul>
<li>SQL commands are <strong>not case-sensitive</strong>. For example, <code>SELECT</code> and <code>select</code> are the same.</li>
<li>Conventionally, keywords are written in uppercase for readability.</li>
</ul>
</li>
<li><strong>Semicolon</strong>:
<ul>
<li>Statements often end with a semicolon (<code>;</code>), especially in scripts.</li>
</ul>
</li>
<li><strong>Comments</strong>:
<ul>
<li>Single-line comments: <code>-- This is a comment</code></li>
<li>Multi-line comments: <code>/* This is a multi-line comment */</code></li>
</ul>
</li>
</ol>
<hr />
<h4><strong>Basic SQL Statement Structure</strong></h4>
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<pre class="language-php"><code>SELECT column1, column2
FROM table_name
WHERE condition
GROUP BY column
HAVING condition
ORDER BY column ASC|DESC;
</code></pre>
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<hr />
<h4><strong>SQL Syntax Examples</strong></h4>
<h5><strong>1. Retrieving Data (<code>SELECT</code>)</strong></h5>
<p>Retrieve all records from a table:</p>
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<pre class="language-php"><code>SELECT * FROM employees;
</code></pre>
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<p><strong>Output:</strong></p>
<table>
<thead>
<tr>
<th>id</th>
<th>name</th>
<th>position</th>
<th>salary</th>
</tr>
</thead>
<tbody>
<tr>
<td>1</td>
<td>John Doe</td>
<td>Manager</td>
<td>75000</td>
</tr>
<tr>
<td>2</td>
<td>Jane Smith</td>
<td>Developer</td>
<td>60000</td>
</tr>
</tbody>
</table>
<hr />
<h5><strong>2. Filtering Data (<code>WHERE</code>)</strong></h5>
<p>Retrieve employees earning more than $50,000:</p>
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<pre class="language-php"><code>SELECT name, salary 
FROM employees 
WHERE salary &gt; 50000;
</code></pre>
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<p><strong>Output:</strong></p>
<table>
<thead>
<tr>
<th>name</th>
<th>salary</th>
</tr>
</thead>
<tbody>
<tr>
<td>John Doe</td>
<td>75000</td>
</tr>
<tr>
<td>Jane Smith</td>
<td>60000</td>
</tr>
</tbody>
</table>
<hr />
<h5><strong>3. Sorting Data (<code>ORDER BY</code>)</strong></h5>
<p>Retrieve all employees and sort them by salary in descending order:</p>
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<pre class="language-php"><code>SELECT name, salary 
FROM employees 
ORDER BY salary DESC;
</code></pre>
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<p><strong>Output:</strong></p>
<table>
<thead>
<tr>
<th>name</th>
<th>salary</th>
</tr>
</thead>
<tbody>
<tr>
<td>John Doe</td>
<td>75000</td>
</tr>
<tr>
<td>Jane Smith</td>
<td>60000</td>
</tr>
<tr>
<td>Alice Brown</td>
<td>50000</td>
</tr>
</tbody>
</table>
<hr />
<h5><strong>4. Inserting Data (<code>INSERT</code>)</strong></h5>
<p>Add a new employee to the table:</p>
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<pre class="language-php"><code>INSERT INTO employees (name, position, salary) 
VALUES ('Alice Brown', 'Analyst', 50000);
</code></pre>
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<hr />
<h5><strong>5. Updating Data (<code>UPDATE</code>)</strong></h5>
<p>Increase salary for all Managers by 10%:</p>
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<pre class="language-php"><code>UPDATE employees
SET salary = salary * 1.10
WHERE position = 'Manager';
</code></pre>
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<hr />
<h5><strong>6. Deleting Data (<code>DELETE</code>)</strong></h5>
<p>Remove an employee by ID:</p>
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<pre class="language-php"><code>DELETE FROM employees 
WHERE id = 3;
</code></pre>
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<hr />
<h4><strong>Tips for Writing SQL Syntax</strong></h4>
<ol>
<li><strong>Use Indentation</strong>: Format complex queries for better readability.</li>
<li><strong>Alias Columns and Tables</strong>: Simplify queries using aliases (e.g., <code>SELECT e.name FROM employees AS e</code>).</li>
<li><strong>Test Queries</strong>: Always test queries on a backup database to avoid accidental data loss.</li>
</ol>
<hr />
<h4>&nbsp;</h4>
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