sqlglot/tests/fixtures/optimizer/optimize_joins.sql

SELECT * FROM x JOIN y ON y.a = 1 JOIN z ON x.a = z.a AND y.a = z.a;
SELECT * FROM x JOIN z ON x.a = z.a AND TRUE JOIN y ON y.a = 1 AND y.a = z.a;

SELECT * FROM x JOIN y ON y.a = 1 JOIN z ON x.a = z.a;
SELECT * FROM x JOIN y ON y.a = 1 JOIN z ON x.a = z.a;

SELECT * FROM x CROSS JOIN y JOIN z ON x.a = z.a AND y.a = z.a;
SELECT * FROM x JOIN z ON x.a = z.a AND TRUE JOIN y ON y.a = z.a;

SELECT * FROM x LEFT JOIN y ON y.a = 1 JOIN z ON x.a = z.a AND y.a = z.a;
SELECT * FROM x JOIN z ON x.a = z.a AND TRUE LEFT JOIN y ON y.a = 1 AND y.a = z.a;

SELECT * FROM x INNER JOIN z ON x.id = z.id;
SELECT * FROM x JOIN z ON x.id = z.id;

SELECT * FROM x LEFT OUTER JOIN z;
SELECT * FROM x LEFT JOIN z ON TRUE;

SELECT * FROM x CROSS JOIN z;
SELECT * FROM x CROSS JOIN z;

SELECT * FROM x JOIN z;
SELECT * FROM x CROSS JOIN z;

SELECT * FROM x FULL JOIN z;
SELECT * FROM x FULL JOIN z ON TRUE;

SELECT * FROM x NATURAL JOIN z;
SELECT * FROM x NATURAL JOIN z ON TRUE;

SELECT * FROM x RIGHT JOIN z;
SELECT * FROM x RIGHT JOIN z ON TRUE;

SELECT * FROM x JOIN z USING (id);
SELECT * FROM x JOIN z USING (id);

SELECT * FROM x CROSS JOIN z ON TRUE;
SELECT * FROM x CROSS JOIN z;