# ksqlDB for Confluent Platform Reference This reference covers SQL syntax, built-in functions, operators, and server configuration for building and operating ksqlDB applications. - [Syntax and Lexical Structure](sql/lexical-structure.md#ksqldb-lexical-structure): Learn the make-up of the SQL language to write programs. - [Built-in functions](../developer-guide/ksqldb-reference/functions.md#ksqldb-reference-functions): Invoke built-in functions shipped with ksqlDB. - [Operators](../developer-guide/ksqldb-reference/operators.md#ksqldb-reference-operators): Call operators that are built in to the language. - [Server Configuration](server-configuration.md#ksqldb-reference-server-configuration): Control how ksqlDB server behaves. - [Metrics](metrics.md#ksqldb-reference-metrics): Observe how your cluster is behaving over time. - [User-defined Functions](user-defined-functions.md#ksqldb-reference-udfs): Extend ksqlDB to invoke custom code written in Java. - [Processing Log](processing-log.md#ksqldb-reference-processing-log): Log internal events that arise when processing rows. - [Serialization Formats](serialization.md#ksqldb-serialization-formats): Control the format of how data is read and written. - [Java Client](../developer-guide/java-client/java-client.md#ksqldb-developer-guide-java-client): Talk to ksqlDB using Java. - [REST API](../developer-guide/ksqldb-rest-api/overview.md#ksqldb-rest-api): Communicate with ksqlDB over an HTTP REST API. - [Quick Reference](../developer-guide/ksqldb-reference/quick-reference.md#ksqldb-reference-quick-reference): Quickly reference the elements of the language.