Table of Contents
WHY IS LEFT join not working SQL?
The reason it does this is because the WHERE clause is evaluated after the LEFT JOIN , which then filters out your NULL results from the LEFT JOIN . Including the right-hand table of a LEFT JOIN (or the left-hand table of a RIGHT JOIN ) in the WHERE clause effectively transforms the OUTER JOIN into an INNER JOIN .
Does LEFT join return all rows?
The SQL LEFT JOIN returns all rows from the left table, even if there are no matches in the right table. This means that a left join returns all the values from the left table, plus matched values from the right table or NULL in case of no matching join predicate.
What does a LEFT join return?
The LEFT JOIN keyword returns all records from the left table (table1), and the matching records from the right table (table2). The result is 0 records from the right side, if there is no match.
Which rows do the LEFT join return?
The LEFT JOIN returns all rows from the left table and the matching rows from the right table. If no matching rows are found in the right table, NULL are used. In this syntax, T1 and T2 are the left and right tables, respectively.
Why we use left join in SQL?
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.
Why would you use a left join?
We use a LEFT JOIN when we want every row from the first table, regardless of whether there is a matching row from the second table. This is similar to saying, “Return all the data from the first table no matter what.
Why we use left join and right join?
The LEFT JOIN includes all records from the left side and matched rows from the right table, whereas RIGHT JOIN returns all rows from the right side and unmatched rows from the left table….LEFT JOIN vs. RIGHT JOIN.
| LEFT JOIN | RIGHT JOIN |
|---|---|
| It is also known as LEFT OUTER JOIN. | It is also called as RIGHT OUTER JOIN. |
When would you choose a left join over an inner join?
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.
When to use left join and inner join in SQL?
Why LEFT join is required?
This join returns all the rows from the left table in conjunction with the matching rows from the right table. If there are no columns matching in the right table, it returns NULL values. This JOIN returns all the rows from the right table in conjunction with the matching rows from the left table.