where.html

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            <h1>SQL WHERE Clause</h1>
            <p>The WHERE clause is used to filter records.</p>
            <p>It is used to extract only those records that fulfill a specified condition.</p>

            <h2>WHERE Syntax</h2>
            <pre><code class="language-sql">SELECT column1, column2, ...
FROM tablename
WHERE condition;</code></pre>

            <h2>WHERE Clause Example</h2>
            <p>The following SQL statement selects all the patients with the gender "F", in the "patients" table:</p>

            <pre><code class="language-sql">SELECT * FROM patients
WHERE gender = 'F';</code></pre>

            <h2>Text Fields vs. Numeric Fields</h2>
            <p>SQL requires single quotes around text values (most database systems will also allow double quotes).</p>
            <p>However, numeric fields should not be enclosed in quotes:</p>

            <pre><code class="language-sql">SELECT * FROM patients
WHERE patient_id = 1;</code></pre>

            <h2>Operators</h2>
            <p>The following operators can be used in the WHERE clause:</p>

            <h3>Equal (=)</h3>
            <pre><code class="language-sql">SELECT * FROM patients
WHERE patient_id = 1;</code></pre>

            <h3>Greater Than (>)</h3>
            <pre><code class="language-sql">SELECT * FROM patients
WHERE patient_id > 5;</code></pre>

            <h3>Less Than (&lt;)</h3>
            <pre><code class="language-sql">SELECT * FROM patients
WHERE patient_id < 5;</code></pre>

            <h3>Greater Than Or Equal To (&gt;=)</h3>
            <pre><code class="language-sql">SELECT * FROM patients
WHERE patient_id >= 5;</code></pre>

            <h3>Less Than Or Equal To (&lt;=)</h3>
            <pre><code class="language-sql">SELECT * FROM patients
WHERE patient_id <= 5;</code></pre>

            <h3>Not Equal (&lt;&gt; or !=)</h3>
            <pre><code class="language-sql">SELECT * FROM patients
WHERE patient_id <> 5;

-- No patient_id 5 row</code></pre>

            <h3>Between (inclusive range)</h3>
            <pre><code class="language-sql">SELECT * FROM patients
WHERE patient_id BETWEEN 4 AND 6;</code></pre>

            <h3>Like (pattern search)</h3>
            <pre><code class="language-sql">SELECT * FROM patients
WHERE first_name LIKE 'a%';

-- First names starting with 'a'.
-- View sql patterns for more info.</code></pre>

            <h3>IN (in a collection)</h3>
            <pre><code class="language-sql">SELECT * FROM patients
WHERE patient_id IN (1, 3, 6, 9);

-- the values can be replaced with a sub-query.</code></pre>
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