SQL : Updating Oracle table with data using subquery


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 :




Desire Output :

EMPLOYEE table :

EMPLOYEE  table 1

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:

Incorrect Example

If we run this example, SQL Developer will report : “SQL Error: ORA-00904: “A”.”SALARY”: invalid identifier “.

The second approach that I made :

Inefficient Example

Running on SQL Developer the script had updated 3 rows from “EMPLOYEE ” table. The result is inefficient. The output was this :

Output 1Finally, 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.

Efficient Example

Running on SQL Developer the script had merged 1 row from “EMPLOYEE ” table. The output was is the correct one:

Desire output


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