sqlis the the main include for ODBC v3.0+ Core functions, corresponding to the
sql.h C header file. It imports publicly etc.c.odbc.sqltypes for conformity with the C header.
Note: The ODBC library itself not a part of the dmd distribution (and typically not a part of the distribution packages of other compilers such as gdc and ldc). To use ODBC, install it per the vendor- and platform-specific instructions and then use the appropriate command-line flags (e.g. for dmd, -L-lodbc on Posix and -Lodbc32.lib on Windows) to link with the ODBC library. On Windows, using pragma(lib, "odbc32") in D code at top level is also appropriate.