<p>SQL SELECT statement is used to retrieve data from database tables 1. The basic structure is SELECT column FROM table; 2. All columns can be selected by *, but it is recommended to specify the required columns clearly to improve performance; 3. The WHERE clause can filter rows according to conditions, such as salary>50000; 4. ORDER BY sort the result by default ascending order, such as department first and salary descending order. </p> <p><img src="/static/imghw/default1.png" data-src="https://img.php.cn/upload/article/000/000/000/175147880376760.jpeg" class="lazy" alt="What is the basic syntax for a SQL SELECT statement?"></p> <p> A basic SQL SELECT statement retrieves data from one or more tables in a database. The simplest form focuss on selecting specific columns or all columns from a single table. </p> <img src="/static/imghw/default1.png" data-src="https://img.php.cn/upload/article/000/000/000/175147880489904.jpeg" class="lazy" alt="What is the basic syntax for a SQL SELECT statement?"><p> Here's the general structure: </p> <img src="/static/imghw/default1.png" data-src="https://img.php.cn/upload/article/000/000/000/175147880651416.jpeg" class="lazy" alt="What is the basic syntax for a SQL SELECT statement?"><pre class='brush:php;toolbar:false;'> SELECT column1, column2, ... FROM table_name;</pre><p> If you want to select all columns, you can use the asterisk ( <code>*</code> ) wildcard:</p><pre class='brush:php;toolbar:false;'> SELECT * FROM table_name;</pre><p> This gives you the full dataset from that table, but in practice, it's often better to specify only the columns you need for clarity and performance. </p><img src="/static/imghw/default1.png" data-src="https://img.php.cn/upload/article/000/000/000/175147880764916.jpeg" class="lazy" alt="What is the basic syntax for a SQL SELECT statement?" /><hr /><h3 id="Selecting-Specific-Columns"> Selecting Specific Columns</h3><p> When you know exactly which columns you need, it's best to list them explicitly instead of using <code>*</code> .</p><p> For example, if you have a table called <code>employees</code> with columns like <code>id</code> , <code>name</code> , <code>department</code> , and <code>salary</code> , and you're only interested in employee names and departments, your query would look like this:</p><pre class='brush:php;toolbar:false;'> SELECT name, department FROM employees;</pre><p> ? <strong>Tips:</strong></p><ul><li> Use commas to separate multiple column names.</li><li> Column order in the result will match the order you list them.</li><li> Aliasing columns can improve readability:<pre class='brush:php;toolbar:false;'> SELECT name AS employee_name, department AS dept FROM employees;</pre></li></ul><hr /><h3 id="Filtering-Rows-with-WHERE-Clause"> Filtering Rows with WHERE Clause</h3><p> Most of the time, you don't want every row — just the ones that meet certain conditions. That's where the <code>WHERE</code> clause comes in handy.</p><p> Say you only want to see employees earning more than $50,000:</p><pre class='brush:php;toolbar:false;'> SELECT name, salary FROM employees WHERE salary > 50000;</pre><p> ? <strong>Common operators used in WHERE:</strong></p><ul><li> <code>=</code> , <code><></code> (not equal)</li><li> <code><</code> , <code>></code> , <code><=</code> , <code>>=</code></li><li> <code>IN</code> , <code>BETWEEN</code> , <code>LIKE</code> , <code>IS NULL</code></li></ul><p> Example with <code>IN</code> :</p><pre class='brush:php;toolbar:false;'> SELECT name, department FROM employees WHERE department IN (&#39;HR&#39;, &#39;IT&#39;);</pre><p> This makes it easy to filter based on multiple values ??without writing long chains of ORs.</p><hr /><h3 id="Sorting-Results-with-ORDER-BY"> Sorting Results with ORDER BY</h3><p> You can sort the output using the <code>ORDER BY</code> clause. By default, sorting is done in ascending order ( <code>ASC</code> ), but you can also specify descending ( <code>DESC</code> ).</p><p> To get employees sorted by salary from highest to lowest:</p><pre class='brush:php;toolbar:false;'> SELECT name, salary FROM employees ORDER BY salary DESC;</pre><p> You can also sort by multiple columns. For instance, first by department, then by salary within each department:</p><pre class='brush:php;toolbar:false;'> SELECT department, name, salary FROM employees ORDER BY department ASC, salary DESC;</pre><p> This helps organize results logically, especially when presenting data to users or analyzes.</p> <hr> <p> That's basically how a simple SELECT works. It gets more powerful when you start joining tables, aggregating data, or using subqueries, but those are for more advanced uses. For day-to-day querying, knowing how to select, filter, and sort is a solid foundation.</p>

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