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 agnostic, and has
a hierarchical structure.sql_build(op, con = NULL, ...)sql_optimise(x, con = NULL, ...)
select_query(from, select = sql("*"), where = character(),
group_by = character(), having = character(), order_by = character(),
limit = NULL, distinct = FALSE)
join_query(x, y, vars, 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, ...)
NULL uses a set of
rules that should be very similar to ANSI 92, and allows for testing
without an active database connection.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.