In Oracle Database 11g , when you need to update values of certain records from one table, and the value and the records to update are determined by a second table, you can use a subquery in the update statement to achieve the update.
Using “EMPLOYEE” and “EMPLOYEE_STAGING” tables as an example , we want to update field “SALARY” – table “EMPLOYEE” with the values from field “SALARY” – table “EMPLOYEE_STAGING”.
Base data :
EMPLOYEE table :
EMPLOYEE_STAGING table :
Desire Output :
EMPLOYEE table :
Because Oracle does not allow multiple tables within the same update statement, we know at least one subquery will be needed. My first approach, which was incorrect, was this:
If we run this example, SQL Developer will report : “SQL Error: ORA-00904: “A”.”SALARY”: invalid identifier “.
The second approach that I made :
Running on SQL Developer the script had updated 3 rows from “EMPLOYEE ” table. The result is inefficient. The output was this :
Finally, I use the MERGE statement. The MERGE
statement was introduced in Oracle to conditionally insert or update data depending on its presence, a process also known as an “upsert”. The MERGE
statement reduces table scans and can perform the operation in parallel if required.
Running on SQL Developer the script had merged 1 row from “EMPLOYEE ” table. The output was is the correct one:
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