oracle merge join
时间: 2023-08-28 10:35:09 浏览: 53
Oracle Merge Join is a type of join operation used in Oracle databases. It is used when two tables need to be joined based on a common column, and both tables are already sorted on that column.
The merge join operation works by comparing the values in the common column of both tables and merging the rows with matching values into a single result set. This method is generally faster than other join methods like nested loops or hash join, especially when dealing with large datasets.
To perform a merge join in Oracle, the following conditions must be met:
- Both tables must be sorted on the join column
- The join column must be indexed
- The query must include an ORDER BY clause to ensure that both tables are sorted correctly
Here's an example of a merge join query in Oracle:
```
SELECT *
FROM table1
MERGE JOIN table2
ON table1.join_column = table2.join_column
ORDER BY table1.join_column;
```