DQL

DQL commonly stands for Data Query Language or Doctrine Query Language, and its meaning depends on context. In academic and database-literacy discussions, DQL is used as a broad label for the subset of SQL that retrieves data, focusing on queries and the SELECT statement. This usage treats SQL as consisting of several sublanguages: DDL (data definition), DML (data manipulation), DCL (data control), and DQL (data query). Not all sources treat DQL as a formal separate language within the SQL standard; rather, it is a conceptual category emphasizing data retrieval tasks such as filtering, sorting, joining, and projecting results.

Doctrine Query Language, the other prominent meaning of DQL, is a database-agnostic query language used by the Doctrine ORM in PHP. DQL allows developers to write queries in terms of application entities and their fields rather than directly in terms of tables and columns. The ORM translates DQL into database-specific SQL, enabling portability across different database systems. DQL syntax resembles SQL in structure but uses entity names, field names, and associations, supporting joins, subqueries, functions, and parameters.

In practice, DQL as a data-retrieval concept helps people discuss the querying role within SQL, while Doctrine DQL is a concrete implementation used within PHP applications to fetch and relate objects through mappings. Users should distinguish the two meanings to avoid confusion: the former is a general category of data queries, the latter a specific ORM query language. See also SQL, DDL, DML, DCL, TCL, Doctrine ORM.