What is "query"

Consultation or query refers to the act of recovering data previously stored in a computerised system from certain parameters and/or filters by means of a specific command or operator. Usually applies to a database relational, through the operator sql select, but can also be used in non-relational databases ("Nosql") or other structured data repositories.

In a system that supports 4 basic operations CRUD (or VEIN: View, Delete, Insert, Change), the query refers to the act of Visualise the information that was previously inserted (and maintained through changes and removals). This operation should be an explicit and well-defined functionality in such a system, and should not lead to side effects (i.e. should not modify the data being consulted). For the purpose of that tag, the consultation operation must also accept parameters in order to restrict the recovered data set (i.e. an operation that simply returns all the data contained in the system indiscriminately does not consist of a query by that definition).

Summary: use this tag when

• Your program/application/script interacts with a data storage system...
• by means of an interface external... (i.e. which is not simple access to the programme’s own data structures)
• through an explicit operation of visualise that data...
• restricted by means of filters and/or others parameters...
• and without side effects. (i.e. displaying the data does not change the system state)
• And your question relates to the correct use of/troubleshooting with this operation.