first-value.html

<!-- SECCIÓN FIRST_VALUE WINDOW FUNCTION -->
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            <h1>SQL FIRST_VALUE() Window Function</h1>

            <p>The <strong>FIRST_VALUE()</strong> function is a window function that returns the first value in an
                ordered partition of a result set.</p>

            <h2>Syntax</h2>
            <pre><code class="language-sql">FIRST_VALUE ( scalar_expression )  
OVER ( 
    [PARTITION BY partition_expression, ... ]
    ORDER BY sort_expression [ASC | DESC], ...
)</code></pre>

            <h2>Parameter Values</h2>
            <ul>
                <li><strong>scalar_expression</strong>: Required. An expression evaluated against the value of the first
                    row in an ordered partition. Can be a column, subquery, or expression that evaluates to a single
                    value. Cannot be a window function.</li>
            </ul>

            <h2>FIRST_VALUE() Example</h2>
            <p>The following SQL statement displays the oldest patient's <strong>birth_date</strong> for the province
                the patient is in:</p>

            <pre><code class="language-sql">SELECT
  patient_id,
  province_id,
  FIRST_VALUE(birth_date) 
    OVER(
      PARTITION BY province_id   -- group by province_id
      ORDER BY birth_date         -- order by birth_date
      ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
    ) AS oldest_birth_date
FROM patients
ORDER BY patient_id;</code></pre>

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