ODBC 中的 Haskell Unicode 列名

Question

I am trying to query some data from a MSSQL database through HDBC and ODBC . I have however run into a problem when trying to query data from a table with unicode in the column names.

Consider the following MWE:

mwe :: IConnection conn => conn -> IO [[SqlValue]]
mwe conn =
  do r <- quickQuery' conn
          "SELECT [Højde] FROM [Table]"
          []
     return r

When executing the above and passing it a connection object to the database i get the following error message:

*** Exception: SqlError {seState = "[\"42S22\",\"42000\"]", seNativeError = -1, seErrorMsg = "execute execute: [\"207: [Microsoft][ODBC Driver 17 for SQL Server][SQL Server]Invalid column name 'H\\195\\184jde'.\",\"8180: [Microsoft][ODBC Driver 17 for SQL Server][SQL Server]Statement(s) could not be prepared.\"]"}

The relevant part most likely being that H\\\\195\\\\184jde is not a valid column name.

My research has mostly led to results about unicode in the parameters to the query. I have tried to use bytestrings instead of normal strings, but since the argument for QuickQuery' is a string that did not help.

Answer 1

I don't have an MS SQL instance to test this, but the code in HDBC-odbc encodes the query using UTF-8. Meanwhile, this documentation suggests that for modern ODBC drivers, the character set used for queries depends on the process locale at the time the driver is initialized. If it's "C" , which is the usual process default, then the driver will use the UTF-8 character set. However, if the process executes:

setlocale(LC_ALL,"")

before initializing the driver, and the current Windows locale is, say, English using the Latin-1 1252 code page, then the ODBC driver will expect Latin-1 encoded queries. Unfortunately for you, the GHC runtime does run setlocale(LC_ALL,"") , so that's probably what's going wrong.

If you reset the locale to "C" at the start of "main" , that may fix the issue:

{-# LANGUAGE ForeignFunctionInterface #-}

import Control.Monad
import Foreign.C
import Foreign.Ptr

foreign import ccall "locale.h setlocale" c_setlocale :: CInt -> CString -> IO CString

setCLocale :: IO ()
setCLocale = do
  rc <- withCString "C" $ c_setlocale 0
  when (rc == nullPtr) $ error "setCLocale failed"

main = do
  setCLocale
  print "whatever"

I'm not sure if this will cause other problems (eg, with terminal input/output). If it does, you may be able to set the locale to "C" before initializing the driver and then reset it to "" right after.