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Introduction

Kwil's database language is the world's first SQL Smart Contract language. It is designed to be a powerful, expressive, and secure language for building decentralized applications. Kwil's language features a subset of standard SQL, with additional features for building data smart contracts.

Features​

SQL Compatibility​

Kwil's language supports standard SQL syntax, such as SELECT, INSERT, UPDATE, and DELETE statements. It also supports normal DDL statements like CREATE TABLE, CREATE INDEX, etc. This makes it easy for developers to get started with Kwil, as they can leverage their existing SQL knowledge.

There are some features that are not supported in Kwil's language, due to them either being insecure for a smart contract language, or simply because they have not been implemented yet. Below is a list of features that are commonly supported in SQL, but are not supported in Kwil:

  • Floating point numbers (only integers and fixed-point decimals are supported)
  • VIEWs (these simply haven't been implemented yet, so if you find yourself wanting these, please let us know!)
  • TRIGGERs (these are not supported because they are insecure for a smart contract language)
  • Stored Procedures (these are not supported because they are insecure for a smart contract language, howevever we do have an "action" feature that is similar)
  • RETURNING clause at the end of an INSERT, UPDATE, or DELETE statement (this simply hasn't been implemented yet, so if you find yourself wanting this, please let us know!)

Actions​

Actions are the primary way in which SQL Smart Contracts are defined. They are pre-defined functions that can be executed by end users. Since end users likely will not have permissions to execute arbitrary INSERT/UPDATE/DELETE statements against your database, they will need to execute pre-defined actions that you have created. Using actions, you can define the SQL statements and associated logic that end users can execute.

Contextual Variables​

Kwil's language supports contextual variables, which allows you to access information about the current transaction, such as the sender's wallet address. This allows you to build smart contracts that respond to the current transaction, and can enforce rules based on the sender's identity. Contextual variables can be referenced using @ followed by the variable name. For example, to access the caller's wallet address in an INSERT statement, you would do:

INSERT INTO table_name (column_name) VALUES (@caller);

A full list of contextual variables can be found below:

Variable NameDescription
@callerThe wallet address (text) of the caller of the current transaction, equivalent to Solidity's msg.sender
@txidThe transaction ID of the current transaction
@signerThe wallet address (bytea) that signed the current transaction
@heightThe block height of the current transaction
@block_timestampThe timestamp of the current block
@authenticatorThe authenticator of the current transaction

Next Steps​

To get started with Kwil's language, check out the Tables guide to learn how to create and manage tables.