The true utility of any database, however, is the ability to query it for certain results, and the commands `search`, `delete` and `slice` all support a simple query language to select which calculation results to interrogate. This query language functions similarly to the filter language for the `digichem result` command. Each query starts by identifying an attribute to search against, for example the HOMO energy, followed by a comparison operator, the most common of which are '<' (less than), '<=' (less than or equal to), '=' (equal to), '==' (exactly equal to, which is case sensitive for text), '>' (greater than) or '>=' (greater than or equal to). Digichem also supports more advanced queries to allow comparison of a single item in a list, and for molecular substructure searching. Each query is then completed with a value to search against. As a full example, the command `digichem database main search orbitals:values:any:label==HOMO:energy:value<-0.5` would retrieve all calculation results from the main Digichem database with a HOMO energy of less than -0.5 eV. Multiple queries can be specified simultaneously and combine in a logical AND fashion, which permits querying for results that fall between a given range.