Difference Between Left and Right Join (With Table)

Join is a typical moniker and command element that will appear from time to time while dealing with SQL. The join clause facilitates the combining of records from various tables in data collection. The join generates a table that may be used alone or combined with one another. It is thus recommended to comprehend these joins and the distinctions between them to determine the specific join as well as whether right or left should be chosen in unique cases.

Left Join vs Right Join

The main difference between left join and right join is that the incorporation of non-matched entries is the primary distinction between both these types of joins. LEFT JOIN processes all entries from the left side as well as paired rows from the right table, whilst RIGHT JOIN delivers all rows from the right side as well as mismatched rows from the left panel.

Even though there is no matching on the right side of the table, the SQL LEFT process incoming all entries from the left table. This implies that when the ON clause contains 0 (zero) entries on the right side of the table, the join would still return a record with NULL within every field from the main table. This implies that a left join delivers all of the data first from the left table, as well as any matched values from the right table, or NULL if no suitable join predicate exists.

The right join, on the other hand, finds that even in the left table, the SQL RIGHT receives and sends all entries from the right table. This implies that even if the ON clause contains 0 (zero) entries in the left database, the join would still produce a row with a NULL value in each field from the left table just like the left join but, vice versa.

This implies that a right join delivers all of the data from the right table, as well as any accepted values from the tables, or NULL if no fitting join predicate exists for this operation.

Comparison Table Between Left and Right Join

Parameters of ComparisonLeft JoinRight Join
UsageIt connects multiple tables and provides all records from the left table as well as matching rows as from right.It joins multiple tables and delivers all data from the right table as well as matching rows first from the left table.
Query ExecutionDuring the implementation of the query including the left join, all the entries of the tables are received first, and then the matching data of the right table column values are obtained using stacked loops, and the NULL value is replaced for other unmatched data.During the implementation of the query including the right join, all data of the right table is obtained first, and afterwards the matched records of the left table column values are collected using stacked loops.
Result SetResult set value will be NULL or zero if no matching data is found in the right table.Result set value will be NULL or zero if no matching data is found in the left table.
Synonymous TermLEFT OUTER JOINRIGHT OUTER JOIN
SyntaxSELECT column_name(s)
FROM table1
LEFT JOIN table2
ON table1.column_name = table2.column_name;
SELECT column_name(s)
FROM table1
RIGHT JOIN table2
ON table1.column_name = table2.column_name;

What is Left Join?

To merge data from two databases depending on a column containing matching values, we use JOIN in SQL. For instance, if you’ve had a table containing client data (client ID, first surname, identifier, etc.) and then another table containing order data for a particular time (transaction ID, time, client ID, product ID, etc.), you may link the two datasets using the columns that include customer ID numbers. This will provide you with order and customer information for each client and the Left join clause plays an essential role in doing this operation.

Let’s look at the syntax of the Left Join to understand its utility properly:

SELECT column_name(s)

FROM table1

LEFT JOIN table2

ON table1.column_name = table2.column_name

  1. ‘SELECT’ – Begin by selecting the categories that we wish to view in the dataset.
  2. ‘FROM’ – Enter the data of the tables, wherein we wish to maintain all of the information.
  3. ‘LEFT JOIN’ – Enter the data of the second table that is mentioned.
  4. ‘ON’ – Use this phrase to specify which fields will be utilized to connect the tables.

To begin, the databases examine each entry in the left table then seek for a match in the right table depending on the linked columns. If a match is found, data from the right table is added to the matching row of the left table. If there are multiple finds which are matching, the column in the left table is duplicated to include all data directly from the right table. If no match is found, it preserves the row as from the left table and then inserts NULL into the relevant columns of the right table.

What is Right Join?

To put it bluntly, the right join operation is very similar to the left join, just the opposite. For better understanding, we will go through the syntax analysis and the general usage of right join as well as the link to the left table is important in this case.

The SQL right join delivers all of the information from the right table’s rows. It also contains the confirmed values as from the left table; however, if no matches are found in both databases, it delivers NULL value. Right joins essentially are very similar to left joins in that they retrieve all rows out from the table specified in the RIGHT JOIN phrase but only corresponding rows from the table specified in the FROM clause.

The RIGHT JOIN is infrequently used since the contents of a RIGHT JOIN may be obtained by simply swapping the labels of the two connected tables in a LEFT JOIN.

The tradition about always using LEFT JOIN arises most likely to make queries easier to understand and verify, although there is not a compelling reason to avoid using RIGHT JOIN. It’s worth mentioning that LEFT JOIN and RIGHT JOIN may also be expressed as LEFT OUTER JOIN as well as RIGHT OUTER JOIN.

The syntax for Right Join is described further below. The operations of the right and left joins are identical, but in reverse order:

SELECT column_name(s)
FROM table1
RIGHT JOIN table2
ON table1.column_name = table2.column_name

Main Differences Between Left Join and Right Join

  1. A left join exhibits all rows from the table’s left side, whereas a right join exhibits all rows from the table’s right side.
  2. A left join is also known as left outer join whereas the right join is also known as right outer join.
  3. The left join contains unmatched records from the left table whereas the right join consists of the unmatched data from the right table.
  4. The left join phrase is more commonly used over the right join phrase.
  5. The formula for left join is all the matching records + unmatched records of the left table whereas the formula for right join is all the matching records + unmatched records of the right table.

Conclusion

When interacting with these different joins, it is vital to know that in a left outer join, all the columns from the left of the table are visible in the database. The results appear regardless of whether matched columns are available in the correct table. It makes no difference whether you use the left or right outer join because the consequences are the same. The process information by a right outside join is the same as that provided by a left outer join.

References

  1. https://www.tutorialspoint.com/sql/sql-left-joins.htm#:~:text=The%20SQL%20LEFT%20JOIN%20returns,matches%20in%20the%20right%20table.&text=This%20means%20that%20a%20left,of%20no%20matching%20join%20predicate.
  2. https://mode.com/sql-tutorial/sql-right-join/#:~:text=Right%20joins%20are%20similar%20to,names%20in%20a%20LEFT%20JOIN%20.

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