> For the complete documentation index, see [llms.txt](https://til.notdu.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://til.notdu.com/database/intro-to-database-systems/tree-indexes-i/selection-conditions.md).

# Selection conditions

The DBMS can use a B+Tree index if the query provides any of the attributes of the search key.

Example: Index on \<a,b,c>

-> Supported: (a=5 AND b=3)

-> Supported: (b=3)

Not all DBMSs support this.

For hash index, we must have all attributes in search key.