How to Select Cars That Have Passed All Tests in a List?

Filtering Cars That Successfully Completed All Tests

Efficiently identifying cars that have passed all required tests from a given list requires a method more sophisticated than simple IN operator checks, especially when dealing with multiple tests. A more accurate approach leverages the power of GROUP BY and HAVING clauses.

Consider this SQL query to select cars that have passed every test in a predefined set:

<code class="language-sql">SELECT carname
FROM PassedTest
GROUP BY carname
HAVING COUNT(DISTINCT testtype) = 4</code>

This query groups results by carname and uses the HAVING clause with COUNT(DISTINCT testtype). This ensures only cars that have passed four distinct test types (assuming four tests are in the list) are included in the output.

For a more comprehensive result, incorporating this as a subquery with the cars table allows retrieval of additional car details:

<code class="language-sql">SELECT *
FROM cars
WHERE carname IN (
    SELECT carname
    FROM PassedTest
    GROUP BY carname
    HAVING COUNT(DISTINCT testtype) = 4
)</code>

This improved query offers a precise and complete selection of cars that successfully passed all tests in the defined list.

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