How to Effectively Emulate MySQL's LIMIT Clause in Oracle SQL Queries?

Replicating MySQL's LIMIT in Oracle SQL

MySQL's LIMIT clause simplifies retrieving a specified number of rows after ordering, crucial for paginating data. Oracle, however, requires a different approach.

Why ROWNUM Isn't Enough

While Oracle's ROWNUM pseudocolumn might seem like a solution, it's applied before the ORDER BY clause. This means using ROWNUM for a range of ordered rows yields unpredictable results.

Effective Subquery Approach

A reliable method involves a subquery to order the data first, then apply ROWNUM for limiting:

<code class="language-sql">SELECT *
FROM (
    SELECT *
    FROM emp
    ORDER BY sal DESC
)
WHERE ROWNUM <= 5;</code>

Defining Upper and Lower Bounds

For more precise control, specifying both minimum and maximum row numbers necessitates a more complex query:

<code class="language-sql">SELECT *
FROM (
    SELECT a.*, ROWNUM rnum
    FROM (
        SELECT * FROM <your_table> ORDER BY <your_column>
    ) a
    WHERE ROWNUM <= :MAX_ROW_TO_FETCH
)
WHERE rnum >= :MIN_ROW_TO_FETCH;</code>

Oracle 12c and Later Enhancements

Oracle 12c and later versions offer a cleaner solution using FETCH FIRST and OFFSET:

<code class="language-sql">-- Retrieve the first 10 rows
SELECT *
FROM sometable
ORDER BY name
FETCH FIRST 10 ROWS ONLY;

-- Retrieve rows 20-30
SELECT *
FROM sometable
ORDER BY name
OFFSET 20 ROWS FETCH NEXT 10 ROWS ONLY;</code>

This streamlined syntax provides a more intuitive way to manage row limits and offsets in Oracle.

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