DQL 是 SQL 的子语言，用于查询 关系模型 数据库 中数据的语言。
Data query language (DQL) is part of the base grouping of SQL sub-languages. DQL statements are used for performing queries on the data within schema objects. The purpose of DQL commands is to get the schema relation based on the query passed to it.
Although often considered part of DML, the SQL SELECT statement is strictly speaking an example of DQL. When adding FROM or WHERE data manipulators to the SELECT statement the statement is then considered part of the DML.