Menu
If I run the following SQL query
SELECT *
FROM A
LEFT JOIN B
ON A.foo=B.foo
WHERE A.date = "Yesterday"
Does the WHERE statement get evaluated before or after the JOIN?
If after, what would be a better way to write this statement so that returns only rows in A from "Yesterday" are joined to B?
852
Six Operations to Order: SELECT, FROM, WHERE, GROUP BY, HAVING, and ORDER BY.
The order of execution can significantly affect the resulting value. Operators have the precedence levels shown in the following table.
After the ORDER BY keyword, add the name of the column by which you'd like to sort records first (in our example, salary). Then, after a comma, add the second column (in our example, last_name ). You can modify the sorting order (ascending or descending) separately for each column.
The go to solution for removing duplicate rows from your result sets is to include the distinct keyword in your select statement. It tells the query engine to remove duplicates to produce a result set in which every row is unique.
It depends on the database.
On SQL Server, run: SET SHOWPLAN_ALL ON then run the query, you will get an idea of what happens when it runs.
70
Your idea of "evaluation" is not correct as SQL is a declarative language.
BTW you can see the query execution plan. In MySQL prefix your query with keyword describe to see the execution plan.
23
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
