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6 Δεκ 2017 · Learn about several methods to update data using subqueries in UPDATE statements to make them more effective and easier to maintain in Oracle SQL.
If you want to update specific rows (ie where the IDs match) you probably want to do a coordinated subquery. However, since you are using Oracle, it might be easier to create a materialized view for your query table and let Oracle's transaction mechanism handle the details.
Subquery Method. The first option is to do an update of the DEST_TAB table using a subquery to pull the correct data from the SOURCE_TAB table. Notice the EXISTS predicate to exclude rows from the DEST_TAB table with no matching row in the SOURCE_TAB table.
A subquery is a SELECT statement nested inside another statement such as SELECT, INSERT, UPDATE, or DELETE. Typically, you can use a subquery anywhere that you use an expression. Consider this following subquery example that uses the products table from the sample database.
Update using correlated subquery This statement uses a correlated subquery to update a single column across multiple rows in the FLIGHTS table. It increases the duration of all BA flights by thirty minutes.
Use the UPDATE statement to change existing values in a table or in the base table of a view or the master table of a materialized view. Prerequisites. For you to update values in a table, the table must be in your own schema or you must have the UPDATE object privilege on the table. For you to update values in the base table of a view:
To define one or more values to be assigned to existing rows in an UPDATE statement. To provide values for conditions in a WHERE clause, HAVING clause, or START WITH clause of SELECT, UPDATE, and DELETE statements. To define a table to be operated on by a containing query.
