What is a left join?

Left Join is a keyword, which is used to select all rows from the left table and also the matched values between the two tables.

What is the meaning of left join?

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.

Why would you use a left join?

Use a left join when you want all the results from Table A, but if Table B has data relevant to some of Table A's records, then you also want to use that data in the same query. Use a full join when you want all the results from both Tables.

What is a left join vs right join?

The main difference between these joins is the inclusion of non-matched rows. 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.

What is the left join condition in SQL?

The SQL LEFT JOIN returns all rows from the left table, even if there are no matches in the right table. This means that if the ON clause matches 0 (zero) records in the right table; the join will still return a row in the result, but with NULL in each column from the right table.

Inner Join, Left Join, Right Join and Full Outer Join in SQL Server | SQL Server Joins

What is difference between left join and left outer join?

There really is no difference between a LEFT JOIN and a LEFT OUTER JOIN. Both versions of the syntax will produce the exact same result in PL/SQL. Some people do recommend including outer in a LEFT JOIN clause so it's clear that you're creating an outer join, but that's entirely optional.

Does left join create duplicates?

Avoiding Duplicates

Again, if we perform a left outer join where date = date, each row from Table 5 will join on to every matching row from Table 4. However, in this case, the join will result in 4 rows of duplicate dates in the joined DataSet (see Table 6).

What are the 4 types of joins in SQL?

Why is left join better than right join?

The most substantial difference between the left and right outer join lies in the unmatched records that are obtained besides matched records. The left join takes all matching records and unmatched records of the left table while the right join takes all matching records and unmatched records of the right table.

Which join is faster in SQL?

In case there are a large number of rows in the tables and there is an index to use, INNER JOIN is generally faster than OUTER JOIN. Generally, an OUTER JOIN is slower than an INNER JOIN as it needs to return more number of records when compared to INNER JOIN.

What are the rules in left join?

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.

What can we use instead of left join?

We can use INNER JOIN or just JOIN. In both the cases we get only the matching rows from both the tables (LEFT and RIGHT).

Is a join or left join more efficient?

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.

What is the opposite of a left join?

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.

How many rows are in a left join?

The total number of rows can be i * j, or less then i * j depending on the join conditions and the data.

Which join is most efficient?

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.

Why is right join rarely ever used?

Wikipedia states: "In practice, explicit right outer joins are rarely used, since they can always be replaced with left outer joins and provide no additional functionality."

What are the 5 basic SQL commands?

How to combine two tables in SQL without join?

What are the most common SQL JOINs?

There are four main types of JOINs in SQL: INNER JOIN, OUTER JOIN, CROSS JOIN, and SELF JOIN.

How to join 5 tables in SQL?

Can a left join remove rows?

The left join clause is used to select all rows from the left table, even if they have or don't have matching in the right table. Delete left join table is used to delete rows from the left table that do not have matching records in the right table.

Are left joins bad?

Left joins are a perfectly acceptable type of join which map onto a very common need: get me all x's, if they have associated y's then get those too. Save this answer.

Can I do 2 left joins in SQL?

Yes, indeed! You can use multiple LEFT JOINs in one query if needed for your analysis.

Can a left join create more rows?

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.