CROSS/OUTER APPLY in MySQL
MySQL lacks direct support for the CROSS APPLY syntax, but alternative approaches can be employed to achieve similar functionality.
Nested Sub-query:
In MySQL, a common alternative is to use a correlated sub-query as a predicate in a JOIN statement. This ensures that the sub-query's results are evaluated for each row in the outer query.
Example:
Given the query:
SELECT ORD.ID ,ORD.NAME ,ORD.DATE ,ORD_HIST.VALUE FROM ORD CROSS APPLY ( SELECT TOP 1 ORD_HISTORY.VALUE FROM ORD_HISTORY WHERE ORD.ID = ORD_HISTORY.ID AND ORD.DATE <p>The equivalent query using a nested sub-query would be:</p><pre class="brush:php;toolbar:false">SELECT ORD.ID ,ORD.NAME ,ORD.DATE ,ORD_HISTORY.VALUE FROM ORD INNER JOIN ORD_HISTORY ON ORD_HISTORY.<primary_key> = (SELECT ORD_HISTORY.<primary_key> FROM ORD_HISTORY WHERE ORD.ID = ORD_HISTORY.ID AND ORD.DATE <p><strong>Direct Sub-query:</strong></p><p>In cases where only a single field from the target table is required, a correlated sub-query can be directly integrated into the SELECT statement:</p><pre class="brush:php;toolbar:false">SELECT ORD.ID ,ORD.NAME ,ORD.DATE ,(SELECT ORD_HISTORY.VALUE FROM ORD_HISTORY WHERE ORD.ID = ORD_HISTORY.ID AND ORD.DATE
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