WHERE before or after join SQL?

By Laura S. Harris
Jul 6, 2021

5 Answers. Logical order becomes important with outer joins and more complex queries: applying WHERE on an OUTER table changes the logic completely. Again, it doesn't matter how the optimiser does it internally so long as the query semantics are maintained by following logical processing order.

Can you use WHERE after join SQL?

To use the WHERE clause to perform the same join as you perform using the INNER JOIN syntax, enter both the join condition and the additional selection condition in the WHERE clause. The tables to be joined are listed in the FROM clause, separated by commas. This query returns the same output as the previous example.

How do I write a SQL join?

The join is done by the JOIN operator. In the FROM clause, the name of the first table ( product ) is followed by a JOIN keyword then by the name of the second table ( category ). This is then followed by the keyword ON and by the condition for joining the rows from the different tables.

What is order of execution in SQL?

The SQL order of execution defines the order in which the clauses of a query are evaluated. Some of the most common query challenges people run into could be easily avoided with a clearer understanding of the SQL order of execution, sometimes called the SQL order of operations.

Which join is like inner join?

The most important and frequently used of the joins is the INNER JOIN. They are also referred to as an EQUIJOIN. The INNER JOIN creates a new result table by combining column values of two tables (table1 and table2) based upon the join-predicate.

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References

• https://stackoverflow.com (Mar 29, 2011) WHERE clause better execute before IN and JOIN or after - Stack Overflow
• https://www.ibm.com (Jul 23, 2021) Db2 for i SQL: Inner join using the WHERE clause - IBM
• https://learnsql.com (Sep 16, 2020) How to Join Two Tables in SQL | LearnSQL.com
• https://www.sisense.com (Jan 7, 2020) SQL Query Order of Execution | Sisense
• https://www.tutorialspoint.com (Jul 23, 2021) SQL - INNER JOINS - Tutorialspoint