SQL.DB interface and Select() implementation

[elh]

sql implements a SQL-backed, SQL-queryable, bitemporal database. This implements the key-value oriented interface of bitempura.DB and provides SQL querying.

There is a new interface in sql with 1 major addition

// Select executes a SQL query (as of optional valid and transaction times).
Select(query squirrel.SelectBuilder, opts ...bt.ReadOpt) (*sql.Rows, error)

Example time traveling SQL query

s := squirrel.Select("type", "SUM(balance)").
    From("balances").
    GroupBy("type").
    OrderBy("SUM(balance) DESC")
rows, err := db.Select(s, bt.AsOfValidTime(t3), bt.AsOfTransactionTime(t2))

Current explorations optimizing for easiness and speed. squirrel for query building and sqlite for test db.

Status

• No support for setting up SQL tables
• All SQL DB functions are unimplemented
• Decide if scoping the sql.DB around a single table makes sense
• Interface changes?
  • Still need to decide what to do about versioning information + public interfaces
  • Consider just promoting a separate interface. KV interface and SQL interface should feel different