It looks like the information here for MySQL is essentially correct, though they use different terminology so it's a bit confusing:
- what most people call a "partial index" doesn't seem to have a name in the MySQL world
- MySQL supports indexes on prefixes of string columns, which is often called a "partial index" in the MySQL world (e.g., bug report, forum post, blog post)
The link given in Wikipedia today as support for "MySQL as of version 5.4 does not support partial indexes" is actually about "functional indexes", which PostgreSQL calls "indexes on expressions". I don't know if this feature has a generic name. The Index (database) article simply refers to this as "indexing on user-defined functions, as well as expressions formed from an assortment of built-in functions".
It is true, however, that MySQL does not currently support partial indexes. Since MySQL uses this term for something else, I don't know of any official documentation that states this, other than looking at the CREATE INDEX documentation and observing that it does not allow a WHERE clause. —Preceding unsigned comment added by 18.104.22.168 (talk) 20:53, 1 October 2010 (UTC)