Why Does My Oracle UPDATE Query with a Join Cause an Infinite Loop?

Update with Join Query in Oracle: Troubleshooting an Infinite Loop

The provided Oracle UPDATE query executes indefinitely, prompting the question of what could be causing this issue. The query attempts to update columns in table1 using a correlated subquery that joins two other tables.

The root cause of the infinite loop is likely due to the absence of a condition in the subquery that would ensure it returns a single row for each row in table1. Without such a condition, the subquery may return multiple rows, which would result in a violation of the UPDATE statement's requirement for a single-row update operation.

To resolve this issue, it is necessary to add a condition to the subquery that relates rows in table1 to rows in the subquery. This would typically involve matching primary or unique keys between the tables using an AND clause. For example:

UPDATE table1 t1 SET (t1.col,t1.Output) = (
  SELECT t2.col, t3.Output + t2.col
  FROM tabl2 t3 
  LEFT JOIN table1 t2 ON t3.Join_Key = t2.Join_Key
  WHERE t2.col is not NULL
    AND t1.some_key = t2.some_key);

In this example, the condition AND t1.some_key = t2.some_key ensures that the subquery will return at most one row for each row in table1, thereby preventing an infinite loop.

Another important consideration is whether the UPDATE statement is intended to update all rows in table1 or only a subset of them. The original query does not contain any WHERE clause, indicating that it would update all rows, which may not be the desired behavior. If only a specific subset of rows should be updated, a WHERE clause should be added to filter the rows that meet the update criteria.

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