What is MERGE statement in Oracle with example?

Merge is one statement that allows you to do either an insert or an update as needed. To use it, you need to state how values in the target table relate to those in the source in the join clause. Then add rows in the when not matched clause. And update them using when matched.

What is Oracle MERGE statement?

The MERGE statement was introduced in Oracle 9i 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.

Is MERGE statement in Oracle performance?

The Oracle “merge” statement combines an insert and update which is why it’s also called an “upsert”. At a high level the merge statement simplifies the syntax, which is essentially a simple “insert, if already exists, update”.

How do you use MERGE statements?

The MERGE statement tries to compare the source table with the target table based on a key field and then do some of the processing. The MERGE statement actually combines the INSERT, UPDATE, and the DELETE operations altogether.

Is MERGE a DML statement?

This statement is a convenient way to combine multiple operations. It lets you avoid multiple INSERT , UPDATE , and DELETE DML statements. MERGE is a deterministic statement. That is, you cannot update the same row of the target table multiple times in the same MERGE statement.

Can we use DELETE in MERGE statement in Oracle?

The Merge statement was introduced in Oracle 9i and improved upon in Oracle 10g. In Oracle 9i only the INSERT and UPDATE parts were supported, in Oracle 10g DELETE was added. DELETE can only occur in the “merge_update_clause” of the above schema. This means that it must occur in the WHEN MATCHED THEN clause.

Can we use parallel hint in MERGE statement?

2 Answers. The PARALLEL hint will enable read-parallelism, but to also enable write-parallelism you will need to either run the above ALTER SESSION command or use the hint /*+ ENABLE_PARALLEL_DML */ .

How can you improve the performance of a MERGE statement in Oracle?

Adding a where-clause in the UPDATE-part to only update records when the values are actually different. If you are merging the same data over and over again and only a smaller subset of the data is actually modified, this will improve performance.

What is the need for MERGE statement?

MERGE statement improves the performance as all the data is read and processed only once whereas in previous versions three different statements have to be written to process three different activities (INSERT, UPDATE or DELETE) in which case the data in both the source and target tables are evaluated and processed …

Can we use DELETE in MERGE statement?

Instead of writing a subquery in the WHERE clause, you can use the MERGE statement to join rows from a source tables and a target table, and then delete from the target the rows that match the join condition.

Is MERGE a DDL statement?

Why we use MERGE statement in Oracle?

Use the MERGE statement to select rows from one or more sources for update or insertion into a table or view. You can specify conditions to determine whether to update or insert into the target table or view. This statement is a convenient way to combine multiple operations.

How does Oracle merge work?

The Oracle MERGE statement selects data from one or more source tables and updates or inserts it into a target table. The MERGE statement allows you to specify a condition to determine whether to update data from or insert data into the target table.

What is SQL MERGE statement?

Merge (SQL) A relational database management system uses SQL MERGE (also called upsert) statements to INSERT new records or UPDATE existing records depending on whether condition matches. It was officially introduced in the SQL:2003 standard, and expanded in the SQL:2008 standard.

What is select in Oracle?

Oracle SELECT Statement. The Oracle SELECT statement is used to retrieve data from one or more than one tables, object tables, views, object views etc. Syntax. 1) expressions: It specifies the columns or calculations that you want to retrieve.