What is Oracle explain plan?

The Oracle explain plan is a statement that returns execution plans for the requested SELECT, UPDATE, INSERT and DELETE statements. The execution plan for any given statement shows the operations in sequence used by Oracle to run that statement.

How do you get the explain plan for a query in Oracle?

EXPLAIN PLAN FOR SELECT last_name FROM employees; This explains the plan into the PLAN_TABLE table. You can then select the execution plan from PLAN_TABLE . See “Displaying PLAN_TABLE Output”.

What is an explain plan in SQL?

UTLXPLP . SQL. This script displays the plan table output including parallel execution columns. DBMS_XPLAN.DISPLAY table function. This function accepts options for displaying the plan table output.

What is cardinality in Explain plan in Oracle?

The cardinality is the estimated number of rows that will be returned by each operation. The Optimizer determines the cardinality for each operation based on a complex set of formulas that use both table and column level statistics as input (or the statistics derived by dynamic sampling).

How do you write an explain plan?

How to generate explain plan in oracle

Explain plan for a sql_id from cursor. set lines 2000 set pagesize 2000 SELECT * FROM table(DBMS_XPLAN.
Explain plan of a sql_id from AWR: SELECT * FROM table(DBMS_XPLAN.
Explain plan of sql baseline:
Explain plan for sql id from sql tuning set:

How do you read a Explain plan query?

To read the SQL Execution Plan correctly, you should know first that the flow of the execution is starting from the right to the left and from the top to the bottom, with the last operator at the left, which is the SELECT operator in most queries, contains the final result of the query.

How do you read an explain plan?

A statement execution plan is the sequence of operations that the database performs to run the statement. Replace the with your SQL Statement. After running this run the following to view the plan: SELECT * FROM table(dbms_xplan.

What is cost in Explain plan Oracle?

Cost is the estimated amount of work the plan will do. A higher cardinality => you’re going to fetch more rows => you’re going to do more work => the query will take longer. Thus the cost is (usually) higher. All other things being equal, a query with a higher cost will use more resources and thus take longer to run.

How cost is calculated in explain plan?

Cost is the estimated amount of work the plan will do. A higher cardinality => you’re going to fetch more rows => you’re going to do more work => the query will take longer. Thus the cost is (usually) higher. The cost is useful for figuring out why the optimizer chose (e.g.) a full table scan over an index.

What are the joins in explain plan?

Both the RBO and CBO support these three join types: nested loop, merge join and hash join. The driving table is read once and for each row in the driving table, the inner table is processed once. The smaller the inner result set, the faster the Nested Loop will perform.

What is explain plan and execution plan in Oracle?

An explain plan predicts how Oracle will process your query. An execution plan describes the steps it actually took. Just as in the driving example above, Oracle may use a different route than the one it predicted.

How do I run a Explain plan in Oracle SQL Developer?

In SQL Developer, you don’t have to use EXPLAIN PLAN FOR statement. Press F10 or click the Explain Plan icon. It will be then displayed in the Explain Plan window.