Mysql explain ref null

Why does lean_users show NULL in the ref column? MySQL IS NULL Optimization. If you run EXPLAIN , such conditions typically only cause the type column to be show ref _or_ null. Whereas, without the check on NULL , it will be ref.

The posts table is then accessed using the eq _ ref access type. This is an internal optimizer object with no user significance. A semijoin operation. That syntax is still recognized for backward compatibility but extended output is now enabled by default , so the EXTENDED keyword is superfluous and deprecated. Let’s take a look at one more example query.

Here we’ll basically take the union of two tables, products and productvariants, each joined with productline. It is not uncommon for an application to use WHERE conditions like this: Actually, this particular one comes from the real worl some years ago. It uses the TINYINT(1) to represent the BOOLEAN values i. Because the IS NULL is a comparison operator, you can use it anywhere that an operator can be used e. The speed of the query depends on your CPU, and for so few rows, also on available RAM, system loa and disk speed. You can use BENCHMARK to run the query several times and time it with higher precision (e.g. you execute it 100times and divide the total time by 10000).

SELECT or WHERE clause. Now in the EXPLAIN plan in the ref there is the value as func. I want to understand what exactly func in this case means and some details regarding this value. EXPLAIN works as EXPLAIN EXTENDED and EXPLAIN EXTENDED has been deprecated.

These notes gives additional information about the query plan, and do not indicate that there is anything wrong about the query. The following query is using the join buffer and I was wondering if someone could explain to me why this is so. Just trying to gain more understanding about mysql and indexing.

The problem is there is a possible_key but no key is chosen. Content reproduced on this site is the property of the respective copyright holders. It is not reviewed in advance by Oracle and does not necessarily represent the opinion of Oracle or any other party. FROM pub JOIN prod ON pub.

Your explain you sent this time is not even using the index. The collect_cmp_types() function has been modified to heading NULLs in the IN list. NULL , and does not scan through the rest of the rows in tthat have the same id value. HTML Tag Reference HTML Event.

In the example above, if any of the UnitsOnOrder values are NULL , the result will be NULL. Won’t work if the query is a prepared statement though. Hi All, I have a JOIN query that joining tables. I have added indexes for all the fields that are using in the where clause.

When I executed the EXPLAIN command for MySql , I got the first line like below. SIMPLE table: departments partitions: NULL type: index possible_keys: PRIMARY key: dept_name key_len: ref : NULL rows: filtered: 100.