Inner Join vs. WHERE Clause in Oracle: Is There a Performance Difference?

Performance difference between INNER JOIN and WHERE clauses in Oracle database

Many people question: In Oracle database, is there a performance difference when using INNER JOIN and WHERE clauses to query data based on common columns from two tables?

The answer is: no performance difference. To prove this, we provide execution plans for two query methods:

-- INNER JOIN执行计划

EXPLAIN PLAN FOR
SELECT * FROM table1 t1
INNER JOIN table2 t2 ON t1.id = t2.id;

SELECT *
FROM TABLE (DBMS_XPLAN.DISPLAY);

-- 0 select statement
-- 1 hash join (access("T1"."ID"="T2"."ID"))
-- 2 table access full table1
-- 3 table access full table2

-- WHERE子句执行计划

EXPLAIN PLAN FOR
SELECT * FROM table1 t1, table2 t2
WHERE t1.id = t2.id;

SELECT *
FROM TABLE (DBMS_XPLAN.DISPLAY);

-- 0 select statement
-- 1 hash join (access("T1"."ID"="T2"."ID"))
-- 2 table access full table1
-- 3 table access full table2

As can be seen from the execution plan, both queries used hash joins for performance optimization and obtained the same results. Therefore, in Oracle, when the goal is to join tables based on common columns, there is no significant performance advantage in choosing INNER JOIN over the WHERE clause.

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