Using SQL to Update an Oracle Table with Data from Another
Oracle SQL offers efficient methods for updating one table with data from another. This can be achieved using correlated updates or alternative syntax.
Let's illustrate with example tables:
Table 1: id | name | description ----------------------- 1 | a | abc 2 | b | def 3 | c | adf
Table 2: id | name | description ----------------------- 1 | x | 123 2 | y | 345
Method 1: Correlated Subquery Update
This approach uses a correlated subquery to fetch matching data from Table 2
for each row in Table 1
:
UPDATE table1 t1 SET (name, description) = (SELECT t2.name, t2.description FROM table2 t2 WHERE t1.id = t2.id) WHERE EXISTS ( SELECT 1 FROM table2 t2 WHERE t1.id = t2.id );
The WHERE EXISTS
clause ensures that only rows with matching IDs in both tables are updated.
Method 2: Alternative Syntax using a Subquery
This method employs a subquery to create a temporary view combining both tables, then updates this view:
UPDATE (SELECT t1.id, t1.name name1, t1.description desc1, t2.name name2, t2.description desc2 FROM table1 t1 JOIN table2 t2 ON t1.id = t2.id) SET name1 = name2, desc1 = desc2;
This approach leverages a JOIN
to efficiently combine the tables. The update then modifies the selected columns (name1
, desc1
) based on the corresponding columns from Table 2
(name2
, desc2
). The id
column serves as the join key, ensuring accurate updates to Table 1
.
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