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SQL Reference Guide
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16. SQL Order of Execution Reference

How the database engine executes SQL query clauses under the hood.

FROM
Return: Value

Step 1: Identify source tables.

Syntax signature:FROM table
Code snippet:
python
Determines query context.
Expected Output:Initial raw set loaded.
Remember: Always ensure correct syntax formatting when calling FROM.
JOIN
Return: Table

Step 2: Combine joined tables on keys.

Syntax signature:JOIN table2 ON keys
Code snippet:
python
Correlates rows.
Expected Output:Composite dataset in memory.
Remember: Always ensure correct syntax formatting when calling JOIN.
WHERE
Return: Value

Step 3: Filter base tables rows before grouping.

Syntax signature:WHERE condition
Code snippet:
python
Discards rows.
Expected Output:Subset of rows.
Remember: Always ensure correct syntax formatting when calling WHERE.
GROUP BY
Return: Value

Step 4: Collapse rows sharing target column values.

Syntax signature:GROUP BY columns
Code snippet:
python
Groups categories.
Expected Output:Aggregated bucket lists.
Remember: Always ensure correct syntax formatting when calling GROUP BY.
HAVING
Return: Value

Step 5: Filter aggregated buckets.

Syntax signature:HAVING group_condition
Code snippet:
python
Discards groups.
Expected Output:Subset of grouped records.
Remember: Always ensure correct syntax formatting when calling HAVING.
SELECT
Return: Table

Step 6: Extract matching columns and assign expressions.

Syntax signature:SELECT columns
Code snippet:
python
Extracts fields.
Expected Output:Selected fields.
Remember: Always ensure correct syntax formatting when calling SELECT.
DISTINCT
Return: Value

Step 7: Deduplicate columns cells.

Syntax signature:DISTINCT
Code snippet:
python
Removes duplicate rows.
Expected Output:Unique output set.
Remember: Always ensure correct syntax formatting when calling DISTINCT.
ORDER BY
Return: Value

Step 8: Sort matching output rows.

Syntax signature:ORDER BY columns
Code snippet:
python
Sorts fields layout.
Expected Output:Sorted result dataset.
Remember: Always ensure correct syntax formatting when calling ORDER BY.
LIMIT
Return: Value

Step 9: Slice resulting rows.

Syntax signature:LIMIT count
Code snippet:
python
Restricts rows count.
Expected Output:Sliced output rows.
Remember: Always ensure correct syntax formatting when calling LIMIT.
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