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Post #914
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SQL EXECUTION ORDER
SQL Doesn’t Run the Way You Think It Does!
Most people assume SQL runs top to bottom—
but in reality, the database follows a completely different process.
Here’s what actually happens when you hit Run:
🔹 FROM & JOIN – First, SQL figures out where to pull the data from.
🔹 WHERE – Then, it filters out rows that don’t match your conditions.
🔹 GROUP BY – If needed, it groups the remaining rows together.
🔹 HAVING – Now, it filters those groups (not individual rows).
🔹 SELECT – Finally, it picks the columns you asked for.
🔹 ORDER BY – It sorts the result.
🔹 LIMIT – At the very end, it restricts the output.
Why does this matter?
⤷ You can’t use column aliases in WHERE
because SELECT runs later.
⤷ Filtering after grouping (HAVING)
is less efficient than filtering before (WHERE).
⤷ Understanding this helps you write faster, better queries.
Most analysts assume SQL reads queries like English.
✅ But databases have their own logic—and mastering it makes
you a 10x better analyst!
SQL Doesn’t Run the Way You Think It Does!
Most people assume SQL runs top to bottom—
but in reality, the database follows a completely different process.
Here’s what actually happens when you hit Run:
🔹 FROM & JOIN – First, SQL figures out where to pull the data from.
🔹 WHERE – Then, it filters out rows that don’t match your conditions.
🔹 GROUP BY – If needed, it groups the remaining rows together.
🔹 HAVING – Now, it filters those groups (not individual rows).
🔹 SELECT – Finally, it picks the columns you asked for.
🔹 ORDER BY – It sorts the result.
🔹 LIMIT – At the very end, it restricts the output.
Why does this matter?
⤷ You can’t use column aliases in WHERE
because SELECT runs later.
⤷ Filtering after grouping (HAVING)
is less efficient than filtering before (WHERE).
⤷ Understanding this helps you write faster, better queries.
Most analysts assume SQL reads queries like English.
✅ But databases have their own logic—and mastering it makes
you a 10x better analyst!
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