Querybyexample

Query by Example (QBE) is a database query language and user interface paradigm that lets users define queries by populating a template rather than writing code. Originating in the 1970s as part of IBM’s research into relational databases, QBE seeks to make data retrieval more approachable for non-programmers.

In a QBE system, the user works with a grid or form that represents one or more tables. Each row corresponds to a potential result pattern, and each column corresponds to an attribute. A user-specified value in a cell establishes a constraint on the corresponding attribute; leaving a cell blank indicates no restriction. Special syntax or separate operator fields allow the expression of comparisons (e.g., =, <, >) or pattern matching (e.g., wildcards). When the example is complete, the system translates the template into a formal query, usually an SQL SELECT statement with appropriate FROM and WHERE clauses. Joins between tables are implied by aligning related attributes in the template.

Benefits include a more declarative view of queries, immediate feedback, and easier construction of simple joins and selections for users familiar with the data schema. QBE influenced later graphical query builders and contributed to the development of declarative querying concepts in database tools. It is still encountered in some database environments and educational settings as a demonstration of query formulation by example.

Limitations include reduced flexibility for complex, nested, or highly specialized queries, and potential scaling challenges on large schemas or dynamic data models.