Federated Syntax

I’ve never used Federated. I’m waiting for the JDBC version capabilities so I can connect to a non MySQL Server (specifically Oracle). In reading the docs, I see that the syntax includes a CONNECTION String.

CREATE TABLE federated_table (
other INT(20) NOT NULL DEFAULT '0',
INDEX name (name),
INDEX other_key (other)

I’m surprised in the state of the syntax for two reasons.

  • First, there are hardcoded variables in the string, this sort of breaks the rules of seperating syntax from authentication specifics
  • Second, if you have multiple FEDERATED tables, you incur a level of duplication of this information, and then multiple necessary changes if the connection string is modified

I can’t ask I’d like to see the following, as I don’t use this syntax, but I’d like to suggest a level of abstraction of this information. Could the CONNECTION point to a referenced object (e.g. CONNECTION=’HOST1′). This would solve my second point. Now, the requirements of the HOST1 object needs to contain a connection string, and where would this be stored. I don’t have an answer for that one. Perhaps somebody else could make a suggestion?

Thanks Mike for your comment, click on comments below to read. Boy it’s been been a long time since I read any ISO Standards documents. Just to clarify Mike’s point for those investigative types. SQL/MED is Management of External Data, and the official ISO document is I believe:

ISO/IEC 9075-9:2003 Information technology – Database Languages – SQL – Part 9: Management of External Data (SQL/MED) ISO Reference

ISO/IEC 9075 defines the SQL language. The scope of the SQL language is the definition of data structure and the operations on data stored in that structure. Parts 1, 2 and 11 encompass the minimum requirements of the language. Others parts define extensions.
ISO/IEC 9075-9:2003 defines extensions to SQL to support management of external data through the use of foreign-data wrappers and datalink types.

This document makes reference to DATALINK, a syntax I remember vaguely from Oracle Days. Will need to vett that. What’s also of note in this document is the reference to using the TABLE TYPE of ‘FOREIGN’.

I wonder why MySQL went with FEDERATED as the TABLE TYPE. I’m sure this is a good reason?


  1. mmpylet says

    We’re actually making federated work a little bit more like SQL/MED (the standard for federated data sources), with an ability to store “server” connection information and refer to it later. Patrick (the person who developed the federated storage engine) already has a working implementation, which should be shipped in 5.2 (MySQL-5.1 is already feature complete).

    We’re also keeping the old format, as for some use cases it’s actually better, especially when trying to do something ad-hoc.