What is outer join in Oracle?
An outer join extends the result of a simple join. An outer join returns all rows that satisfy the join condition and also returns some or all of those rows from one table for which no rows from the other satisfy the join condition.
When should outer join be used?
We use the SQL OUTER JOIN to match rows between tables. We might want to get match rows along with unmatched rows as well from one or both of the tables. We have the following three types of SQL OUTER JOINS. Let’s explore each of SQL Outer Join with examples.
How use outer join in Oracle?
The syntax for the Oracle RIGHT OUTER JOIN is: SELECT columns FROM table1 RIGHT [OUTER] JOIN table2 ON table1. column = table2.
Does outer join use index?
And here is the same query with a Left Outer Join, as it is written in the view. This does NOT use any of the indexes and runs very slowly. — BAD, does not use indexes select TD.
What left outer join do?
Left Outer Join returns all the rows from the table on the left and columns of the table on the right is null padded. Left Outer Join retrieves all the rows from both the tables that satisfy the join condition along with the unmatched rows of the left table.
Is Outer join same as full join?
The FULL OUTER JOIN keyword returns all records when there is a match in left (table1) or right (table2) table records. Tip: FULL OUTER JOIN and FULL JOIN are the same.
Why We Need left outer join?
Left Outer Join: Left Outer Join returns all the rows from the table on the left and columns of the table on the right is null padded. Left Outer Join retrieves all the rows from both the tables that satisfy the join condition along with the unmatched rows of the left table.
How can I improve my left outer join in Oracle?
The performance techniques include:
- General READ SQL optimization for DB2 and Oracle. Optimize queries based on the query optimization guidelines. Push predicates into the OUTER JOIN clause whenever possible. Duplicate constant condition for different tables whenever possible.
- Using common expression syntax in Oracle.
Is outer join in DBMS?
Database Management System (DBMS) allows retrieving data from more than one table using joins. Joins are mainly Cartesian product of two or more relations (or tables). SQL Joins are broadly categorized as Inner Join and Outer Join. Inner Join selects rows from the tables that fulfills the join condition.
How to use the OUTER JOIN operator (+) in Oracle?
If the OUTER join operator ‘ (+)’ appears with the column of table A, Oracle returns all rows of table B and table A returns NULL for all rows that have no matching row (s). The columns in the conditions need not be part of the SELECT list. SELECT Table1.Column_1, Table2.Column_n FROM Table1, Table2 WHERE Table1.Column_2 (+) = Table2.Column_2;
What is the FULL OUTER JOIN in SQL?
Code language: SQL (Structured Query Language) (sql) For each row in the T1 table, the full outer join compares it with every row in the T2 table. If rows from both tables meet the join_condition, the full outer join includes columns of both rows in the result set. We say that the row in T1 table matches with the row in the T2 table in this case.
What is a join query in Oracle?
A JOIN is a query that combines rows from two or more Tables, View or Materialized View. There are four Oracle proprietary joins, an OUTER join is one of them. An OUTER join returns all rows that satisfy the join condition and also returns non-matching rows from one table and for those non-matching rows other table returns null.
Why OUTER JOIN operator returns only matched rows?
But in the second example, OUTER join operator (+) appears in Dept table (Alias name is D) and it returns only matching rows because all rows of Emp table matched with Dept table rows and there is no any unmatched row in Emp table. That’s why it returns only matched rows.