SQLY: write SQL in SQL

SQL is a fantastic language — one of the most successful programming languages in the world. We should use it, not try to replace it with a bespoke DSL.

Yet there are a couple of things that are nice to have help with in constructing SQL queries:

• dialect-aware safe value substitution: Every database interface has its own syntax for substituting values safely (not to allow SQL injection) — for example, $1 or ? or :varname. They also have different requirements for the format of the sql + values argument lists. I want to able to write my queries with the same value substituion syntax, regardless of which database interface I am using, and know that the SQL will be output correctly for my interface, and that the values will be passed to the database engine safely.
• dynamic attributes: In many applications, I don't know in advance which attributes I am going to select, insert, update, or filter by. I want to SELECT a given list of attributes, or filter WHERE a given key/value mapping, or UPDATE or INSERT particular attributes, without having to rewrite the SQL query.
• block composition: Some SQL queries are very complex. I want to able to compose blocks of SQL into larger queries, so that I can manage this complexity effectively. (Most database query DSLs are unable to deal with complex queries, or they invent a hard-to-learn language for writing those queries. Learning SQL is a better use of our time, but it would be very helpful having some assistance managing/manipulating the different blocks in a query.)

SQLY:

• Dynamic value replacement, rendered in one of the supported dialects: postgres ($1), sqlalchemy (:varname), embedded (:varname), mysql (%(varname)s), sqlite (?). Default style is embedded / :varname.
• Dynamic attribute/value lists in SELECT, WHERE, INSERT, and UPDATE syntax.
• Block composition.
• DB-API 2.0 compatibility.