QL language reference¶

Learn all about QL, the powerful query language that underlies the code scanning tool CodeQL.

• About the QL language: QL is the powerful query language that underlies CodeQL, which is used to analyze code.

• Predicates: Predicates are used to describe the logical relations that make up a QL program.

• Queries: Queries are the output of a QL program. They evaluate to sets of results.

• Types: QL is a statically typed language, so each variable must have a declared type.

• Modules: Modules provide a way of organizing QL code by grouping together related types, predicates, and other modules.

• Signatures: Signatures provide a typing mechanism to parameters of parameterized modules.

• Aliases: An alias is an alternative name for an existing QL entity.

• Variables: Variables in QL are used in a similar way to variables in algebra or logic. They represent sets of values, and those values are usually restricted by a formula.

• Expressions: An expression evaluates to a set of values and has a type.

• Formulas: Formulas define logical relations between the free variables used in expressions.

• Annotations: An annotation is a string that you can place directly before the declaration of a QL entity or name.

• Recursion: QL provides strong support for recursion. A predicate in QL is said to be recursive if it depends, directly or indirectly, on itself.

• Lexical syntax: The QL syntax includes different kinds of keywords, identifiers, and comments.

• Name resolution: The QL compiler resolves names to program elements.

• Evaluation of QL programs: A QL program is evaluated in a number of different steps.

• QL language specification: A formal specification for the QL language. It provides a comprehensive reference for terminology, syntax, and other technical details about QL.