sql_build: Build and render SQL from a sequence of lazy operations
In sctyner/dplyr050: A Grammar of Data Manipulation

sql_build creates a select_query S3 object, that is rendered to a SQL string by sql_render. The output from sql_build is designed to be easy to test, as it's database diagnostic, and has a hierarchical structure.

sql_build(op, con, ...)

select_query(from, select = sql("*"), where = character(),
  group_by = character(), having = character(), order_by = character(),
  limit = NULL, distinct = FALSE)

join_query(x, y, type = "inner", by = NULL, suffix = c(".x", ".y"))

semi_join_query(x, y, anti = FALSE, by = NULL)

set_op_query(x, y, type = type)

sql_render(query, con = NULL, ...)

`op`	A sequence of lazy operations
`con`	A database connection. The default `NULL` uses a set of rules that should be very similar to ANSI 92, and allows for testing without an active database connection.
`...`	Other arguments passed on to the methods. Not currently used.

sql_build is generic over the lazy operations, lazy_ops, and generates an S3 object that represents the query. sql_render takes a query object and then calls a function that is generic over the database. For example, sql_build.op_mutate generates a select_query, and sql_render.select_query calls sql_select, which has different methods for different databases. The default methods should generate ANSI 92 SQL where possible, so you backends only need to override the methods if the backend is not ANSI compliant.