Trino, with its robust query engine, offers various types of joins to facilitate seamless data integration and analysis. Understanding these join types and how they are optimized can significantly enhance query performance and streamline analytical workflows. In this detailed guide, we explore the different types of joins supported by Trino and delve into the optimization techniques employed to maximize efficiency.
Inner Joins: Inner joins in Trino return rows when there is at least one match in both tables being joined. These joins are optimized for performance by leveraging techniques such as broadcast join and partition pruning.
Example:
SELECT *
FROM table1
INNER JOIN table2 ON table1.id = table2.id;
Output:
+----+--------+-----+--------+
| id | name | id | value |
+----+--------+-----+--------+
| 1 | Anand | 1 | 100 |
| 2 | Baby | 2 | 200 |
| 3 | Chandy | 3 | 300 |
+----+--------+-----+--------+
Left Joins: Left joins in Trino return all rows from the left table and matching rows from the right table, with nulls in place where there is no match. These joins are optimized using techniques such as block nested loop join and hash join.
Example:
SELECT *
FROM table1
LEFT JOIN table2 ON table1.id = table2.id;
Output:
+----+--------+------+--------+
| id | name | id | value |
+----+--------+------+--------+
| 1 | Anand | 1 | 100 |
| 2 | Baby | 2 | 200 |
| 3 | Chandy| NULL | NULL |
+----+--------+------+--------+
Right Joins: Right joins in Trino return all rows from the right table and matching rows from the left table, with nulls in place where there is no match. Similar optimization techniques as left joins are applied for efficiency.
Full Outer Joins: Full outer joins in Trino return all rows from both tables being joined, with nulls in place where there is no match. These joins are optimized using techniques such as merge join and sort-merge join.
Example:
SELECT *
FROM table1
FULL OUTER JOIN table2 ON table1.id = table2.id;
+----+--------+------+--------+
| id | name | id | value |
+----+--------+------+--------+
| 1 | Anand | 1 | 100 |
| 2 | Baby | 2 | 200 |
| 3 | Chandy| NULL | NULL |
| NULL| NULL | 4 | 400 |
+----+--------+------+--------+
Cross Joins: Cross joins in Trino produce the Cartesian product of the two tables being joined, resulting in every possible combination of rows. While inherently less optimized due to the potential for large result sets, Trino employs optimization techniques such as block nested loop join to enhance performance where possible.
Example:
SELECT *
FROM table1
CROSS JOIN table2;
+----+--------+------+--------+
| id | name | id | value |
+----+--------+------+--------+
| 1 | Anand | 1 | 100 |
| 2 | Baby | 1 | 100 |
| 3 | Chandy| 1 | 100 |
| 1 | Anand | 2 | 200 |
| 2 | Baby | 2 | 200 |
| 3 | Chandy| 2 | 200 |
| ...| ... | ... | ... |
+----+--------+------+--------+
