SQL Sync proposal

[abourget]

First draft proposal, please comment on.

Here's what a SQL Sync config could look like:

sqlsync:
  tables_prefix: "eosio_chain1_"  # Global prefix, for all tables

  whitelist_contracts:
    "*":
      tables: "*"

    # - or -

    eosio.token:
      tables: ["table1", "table2", "table3"]

  blacklist_contracts:
  - skipcontract
  - skipcontract2
  - skipcontract3

  mappings:
  - label: "All currency contracts"

    # Select which contracts, tables, these mappings apply to
    contracts: "*"
    scopes: "*"
    tables: ["accounts"]

    # If set to true, use:
    #    [prefix]_[contract]_[table]_[scope]
    # instead of:
    #    [prefix]_[contract]_[tableName]
    scoped_table_name: false  # Mutually opposed to `scope_as_field`.
    scope_as_field: true  # Creates a compound primary key (_key, _scope)

    # If true, include the contract name in the SQL table name
    # Otherwise, strips  `[contract]_` from SQL tables names.
    full_table_name: true  

    # Some mapping definitions
    sql_type_by_field:
      amount: "character varying(26)"
      memo: "varchar(255) | STRING(?)"
    sql_type_by_type:  # For other fields
      string: "varchar(64)"

  - label: "Positions"
    contracts: ["nav_past", "nav_going"]
    scopes: "*"
    tables: ["positions"]

    # Some ways of combining some fields into one when in SQL, etc..
    sql_type_by_field:
      lat: "character varying(26) | POINT({lat}, {lon})"
      lon: "SKIP"
    sql_type_by_type:  # For other fields
      string: "varchar(64)"