Query planners use JOIN order to optimize how data is combined—help it out by joining smartly.
The order and structure of your SQL joins can significantly impact performance—especially when working with large tables or complex multi-join queries. Most query planners attempt to reorder joins automatically for efficiency, but providing hints through smart design can dramatically improve execution time.
As a general rule, join smaller tables first when possible, especially in hash join scenarios. This minimizes intermediate result sizes and reduces memory consumption. For example, switching the position of a 100-row table to precede a 1-million-row table in a join can cut processing time by half or more.
Additionally, applying filters early—either in WHERE clauses or as subqueries—helps the database reduce rows before performing the join. Instead of joining two full tables and filtering afterward, it’s far more efficient to narrow one or both tables first.
Galaxy’s AI optimizer detects inefficient join orders and rewrites them automatically. It also flags missed opportunities for pre-join filtering, helping you cut compute costs while speeding up large reporting or analytics workloads. With the right join order, many queries can see 1.5x to 5x faster execution.
SELECT * FROM large_table lt JOIN small_table st ON lt.id = st.id;
SELECT * FROM small_table st JOIN large_table lt ON st.id = lt.id;
1.5–5x faster with better join ordering
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