Indexing for BINARY LIKE operations in MySQL

问题

I know that varchar_pattern_ops exists in Postgresql for fast, index-based searches in a LIKE query, but is there any similar functionality for MySQL?

I currently have a Django-MySQL setup where I have this query which runs on a non-indexed field and with a BINARY LIKE operation, and it takes over a minute to complete.

My query is a partial search from the beginning of the text - text%.

This is the table structure. The table actually contains over 20 fields, but I've included just the primary key and the field I'm searching on

+---------+---------------+------+-----+---------+-------+

| Field   | Type          | Null | Key | Default | Extra |

+-------------------------+---------------+------+-----+--

| id      | varchar(255)  | NO   | PRI | NULL    |       |

| mid     | varchar(255)  | NO   | MUL | NULL    |       |

And this is the query -

select count(*) from table where mid binary like 'text%';

These are the indexes -

PRIMARY KEY index has cardinality 102820460
mid index has cardinality 756032

回答1:

Do the fact that MySQL indexes the left side of a string.

Then a string column can use the index if the query use wildcard right side :

 SELECT * FROM your_table WHERE field LIKE "text%" # can use an index

but remember that for index there is a limit of 767 bytes

From Mysql DOC

A B-tree index can be used for column comparisons in expressions that use the =, >, >=, <, <=, or BETWEEN operators. The index also can be used for LIKE comparisons if the argument to LIKE is a constant string that does not start with a wildcard character.

https://dev.mysql.com/doc/refman/8.0/en/index-btree-hash.html

来源：https://stackoverflow.com/questions/55685275/indexing-for-binary-like-operations-in-mysql