[racket] DB and named query parameters

From: Sean McBeth (sean.mcbeth at gmail.com)
Date: Sun Feb 16 11:14:52 EST 2014

aaah, okay, thanks.

On Sun, Feb 16, 2014 at 11:13 AM, Ryan Culpepper <ryanc at ccs.neu.edu> wrote:

> On 02/15/2014 05:11 PM, Sean McBeth wrote:
>> All of the examples in the documentation for the db package use either
>> question-mark placeholders or numbered placeholders, i.e.
>> "select * from some_table where some_column = ?"
>> "select * from some_table where some_column = $1"
>> The three databases that I use (SQL Server, MySQL, and Postgres) all
>> support the question mark syntax, but you can only refer to a single
>> parameter once in a query with the question mark.
>> MySQL and Postgres support numbered parameters, but SQL Server does not.
>> Or at least, not that I'm aware of. I've never seen anyone use it that
>> way, and I can't find any examples online.
>> Regardless, I rather much prefer named parameters, anyway, as it makes
>> the queries easier to read.
>> "select * from some_table where some_column = $param1"
>> I know MySQL, Postgres, AND SQL Server all can support this style (well,
>> replacing $ with @ for SQL Server), because I have a boat load of C#
>> code doing it right now.
>> But there is no indication of how to execute such a query in Racket with
>> DB.
> The PostgreSQL server itself only supports "$N" parameters. The MySQL
> server (AFAIK) only supports "?" parameters.
> Support for other parameter syntaxes may be added by the particular
> library or driver you're using to communicate with the back end. For
> example, I think ODBC drivers all support "?" placeholders.
> The Racket db library doesn't add support for other parameter syntaxes,
> and I have no plans to add it. (Not in terms of rewriting strings of SQL
> code, anyway; possibly from a structured representation of SQL code.)
> You could write the translation(s) using proper tokenizer(s) or regexps
> that happen to work on the queries in your program and then create a
> statement wrapper using prop:statement that would run the translator for
> the appropriate dialect.
> Ryan
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