Inner join returns only the matching rows between both the tables, non matching rows are eliminated. Left Join or Left Outer Join returns only the matching rows between both the tables, plus non matching rows from the left table.
Different Types of SQL JOINs
(INNER) JOIN : Returns records that have matching values in both tables. LEFT (OUTER) JOIN : Returns all records from the left table, and the matched records from the right table. RIGHT (OUTER) JOIN : Returns all records from the right table, and the matched records from the left table.
In SQL, a join is used to compare and combine — literally join — and return specific rows of data from two or more tables in a database. An inner join finds and returns matching data from tables, while an outer join finds and returns matching data and some dissimilar data from tables.
Inner joins have no variations, but outer joins can be left joins, right joins, or full joins. A left outer join returns all records from the left table and matching records from the right table. A right outer join returns all records from the right table and matching records from the left table.
Four types of joins: left, right, inner, and outer. In general, you'll only really need to use inner joins and left outer joins.
B. LEFT JOIN
This join returns all the rows of the table on the left side of the join and matches rows for the table on the right side of the join. For the rows for which there is no matching row on the right side, the result-set will contain null. LEFT JOIN is also known as LEFT OUTER JOIN.
If the tables involved in the join operation are too small, say they have less than 10 records and the tables do not possess sufficient indexes to cover the query, in that case, the Left Join is generally faster than Inner Join. As you can see above, both the queries have returned the same result set.
Theta Join, Equijoin, and Natural Join are called inner joins.
You can use an INNER JOIN operation in any FROM clause. This is the most common type of join. Inner joins combine records from two tables whenever there are matching values in a field common to both tables. You can use INNER JOIN with the Departments and Employees tables to select all the employees in each department.
The INNER JOIN keyword selects all rows from both tables as long as there is a match between the columns in both tables. The LEFT JOIN keyword returns all rows from the left table (table1), with the matching rows in the right table (table2). The result is NULL in the right side when there is no match.
A join combines the set of two tables only. A left join is used when a user wants to extract the left table's data only. Left join not only combines the left table's rows but also the rows that match alongside the right table.
LEFT JOIN , also called LEFT OUTER JOIN , returns all records from the left (first) table and the matched records from the right (second) table. If there is no match for a specific record, you'll get NULLs in the corresponding columns of the right table.
INNER JOIN vs LEFT JOIN? Actually, that is not the question at all. You'll use INNER JOIN when you want to return only records having pair on both sides, and you'll use LEFT JOIN when you need all records from the “left” table, no matter if they have pair in the “right” table or not.
There are few ways to combine the two tables without a common column including Cross Join (Cartesian Product) and UNION.
The biggest difference between an INNER JOIN and an OUTER JOIN is that the inner join will keep only the information from both tables that's related to each other (in the resulting table). An Outer Join, on the other hand, will also keep information that is not related to the other table in the resulting table.
It is possible to use multiple join statements together to join more than one table at the same time. To do that you add a second INNER JOIN statement and a second ON statement to indicate the third table and the second relationship.
Yes, you can.
Using an INNER JOIN with two, three, four, or many more tables is possible. You simply add the INNER JOIN keyword to the end of the join criteria for the previous join. The syntax looks like this: SELECT your_columns FROM table1 INNER JOIN table2 ON table1.
TLDR: The most efficient join is also the simplest join, 'Relational Algebra'. If you wish to find out more on all the methods of joins, read further. Relational algebra is the most common way of writing a query and also the most natural way to do so.
Inner Join is one of the most frequently used joins. The left and right tables are joined by predicates. Only the rows that appear in both the left table and the right table meet the condition. It means the rows are in the set intersection of the left and right tables.
The Merge join is the most efficient join in SQL Server. In simple terms, if you see a Merge Join, your query plan is an efficient query plan and you do not need to do many changes to improve query performances. Since the Merge Join operator uses sorted data inputs, it can use any two large datasets.
Left Outer Join returns all of the rows in the current data and all the data from the matching rows in the joined data, adding rows when there is more than one match. This can result in an expanded row count.
One of the easiest ways to remove duplicate data in SQL is by using the DISTINCT keyword. You can use the DISTINCT keyword in a SELECT statement to retrieve only unique values from a particular column.
LEFT JOIN will return all the records from the left table and only the matching rows from the right table. RIGHT JOIN will do exactly the opposite. It outputs all the records from the right table and the matching rows from the left one.
If you dont include the items of the left joined table, in the select statement, the left join will be faster than the same query with inner join. If you do include the left joined table in the select statement, the inner join with the same query was equal or faster than the left join.