Some databases extend the energy of indexing by permitting indexes to become produced on functions or expressions. For instance, a catalog might be produced on upper(last_title), which may only keep upper situation versions from the last_title area within the index. An alternative choice sometimes supported is using "strained" indexes, where index records are produced just for individuals records that satisfy some conditional expression. An additional facet of versatility would be to permit indexing on user-defined functions, in addition to expressions created from a variety of built-in functions.
what exactly are individuals databases that support flexible indexes which may be:
- On calculated column like: (col1 + col2) * 100
- strained indexes.
- indexing on user-defined functions.
and what's known terminology with this feature?
So far as I understand, all major RDBSs support this feature. I have personally tried on the extender on MySQL and PostgreSQL, however i could be shocked whether it wasn't obtainable in MSSQL and Oracle.
Regrettably, I don't know any special term with this.
In oracle they're known as function based indexes.
For blocking you may be tricky and make up a function that returns the worthiness when the filter matches or null whether it does not. Nulls aren't saved in btree indexes therefore the index is basically strained. You just need to make certain you apply the same function inside your queries.
In my opinion in sql server you may create a calculated column and index that.
SQL Server 2000+ (a minimum of) supports indexes on function-based posts and calculated posts. Indexes on functions could be duplicated using indexed sights on functions.
You will find conditions of course but mainly around determinism (that is most likely universal)
SQL Server 2008+ has strained indexes.
AFAIK, there's no special term. They are just indexes.