FreeTDS Development Group

["Lowden, James K" <LowdenJK AT bernstein.com>]

> From: Thompson, Bill D (London)
> Sent: Friday, November 11, 2005 11:20 AM
> 
> From the thread it looks very much like DBD:Sybase is using the
> ct_dynamic() method in ct-library, which supports placeholders as
> you say.  It seems to be segmenting on ct_send(CS_DESCRIBE_INPUT).
> 
> ct_dynamic() and friends are now implemented in the latest snapshot,
> with one significant exception.  Unfortunately, this is the
> CS_DESCRIBE_INPUT parameter to ct_send(), when using SQL server.
> 
> Sybase supports this functionality by a bespoke TDS message which
> describes the number, type etc of your placeholders.  SQL Server
> has no means that I could discover of providing this information
> to a client.

Hi Bill, 

I had a vague feeling I was understating your progress with ct-lib
placeholders.  Sorry about that.  Thanks for straightening me out.  

It looks like the ODBC analog to CS_DESCRIBE_INPUT is
SQLDescribeParam().  This link provides sample source code.  

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/odbcsql
/od_odbc_d_1not.asp

I see that we don't implement SQLDescribeParam() in our ODBC driver
either. :-(

And I see why. :-(

I compiled their source against their library made this call:

        "select * from systypes where name = ? "

I then called SQLDescribeParam() and used windump to get this answer:

[log in reply]
...      0001 0000 e317 0002 0a75 0073 005f 0065        .........u.s._.e
0x00d0   006e 0067 006c 0069 0073 0068 0000 ab70        .n.g.l.i.s.h...p
0x00e0   0047 1600 0001 0027 0043 0068 0061 006e        .G.....'.C.h.a.n
0x00f0   0067 0065 0064 0020 006c 0061 006e 0067        .g.e.d...l.a.n.g
0x0100   0075 0061 0067 0065 0020 0073 0065 0074        .u.a.g.e...s.e.t
0x0110   0074 0069 006e 0067 0020 0074 006f 0020        .t.i.n.g...t.o..
0x0120   0075 0073 005f 0065 006e 0067 006c 0069        .u.s._.e.n.g.l.i
0x0130   0073 0068 002e 000b 4100 4300 3200 4b00        .s.h....A.C.2.K.
0x0140   4100 4d00 4100 3000 3800 3400 3800 0000        A.M.A.0.8.4.8...
0x0150   00ad 3600 0171 0000 0116 4d00 6900 6300        ..6..q....M.i.c.
0x0160   7200 6f00 7300 6f00 6600 7400 2000 5300        r.o.s.o.f.t...S.
0x0170   5100 4c00 2000 5300 6500 7200 7600 6500        Q.L...S.e.r.v.e.
0x0180   7200 0000 0000 0800 0332 e313 0004 0434        r........2.....4
0x0190   0030 0039 0036 0004 3400 3000 3900 3600        .0.9.6..4.0.9.6.
0x01a0   fd00 0000 0000 0000 00                         .........

[to server]
0x0000   4500 00a2 2eb1 4000 8006 0000 0a51 24a0        E.....@......Q$.
0x0010   0a50 3adc 1252 09c4 39ce de32 cad3 4948        .P:..R..9..2..IH
0x0020   5018 4205 74b1 0000 0101 007a 0000 0100        P.B.t......z....
0x0030   5300 4500 5400 2000 4600 4d00 5400 4f00        S.E.T...F.M.T.O.
0x0040   4e00 4c00 5900 2000 4f00 4e00 2000 7300        N.L.Y...O.N...s.
0x0050   6500 6c00 6500 6300 7400 2000 2000 6e00        e.l.e.c.t.....n.
0x0060   6100 6d00 6500 2000 6600 7200 6f00 6d00        a.m.e...f.r.o.m.
0x0070   2000 7300 7900 7300 7400 7900 7000 6500        ..s.y.s.t.y.p.e.
0x0080   7300 2000 5300 4500 5400 2000 4600 4d00        s...S.E.T...F.M.
0x0090   5400 4f00 4e00 4c00 5900 2000 4f00 4600        T.O.N.L.Y...O.F.
0x00a0   4600                                           F.

[to client]
0x0000   4500 0063 fbfb 4000 7d06 8d7c 0a50 3adc        E..c..@.}..|.P:.
0x0010   0a51 24a0 09c4 1252 cad3 4948 39ce deac        .Q$....R..IH9...
0x0020   5018 4274 ee3b 0000 0401 003b 003b 0100        P.Bt.;.....;.;..
0x0030   fd01 00b9 0000 0000 0081 0100 0001 0a00        ................
0x0040   e700 0109 0400 0100 046e 0061 006d 0065        .........n.a.m.e
0x0050   00fd 0100 c100 0000 0000 fd00 00ba 0000        ................
0x0060   0000 00                                        ...

[to server]
0x0000   4500 0165 2ebf 4000 8006 0000 0a51 24a0        E..e..@......Q$.
0x0010   0a50 3adc 1252 09c4 39ce deac cad3 4983        .P:..R..9.....I.
0x0020   5018 41ca 7574 0000 0301 013d 0000 0100        P.A.ut.....=....
0x0030   ffff 0d00 0000 0001 2604 04ff ffff ff00        ........&.......
0x0040   0063 2200 0000 0904 0001 0022 0000 0040        .c"........"...@
0x0050   0050 0031 0020 006e 0076 0061 0072 0063        .P.1...n.v.a.r.c
0x0060   0068 0061 0072 0028 0031 0032 0038 0029        .h.a.r.(.1.2.8.)
0x0070   0000 0063 5000 0000 0904 0001 0050 0000        ...cP........P..
0x0080   0073 0065 006c 0065 0063 0074 0020 002a        .s.e.l.e.c.t...*
0x0090   0020 0066 0072 006f 006d 0020 0073 0079        ...f.r.o.m...s.y
0x00a0   0073 0074 0079 0070 0065 0073 0020 0077        .s.t.y.p.e.s...w
0x00b0   0068 0065 0072 0065 0020 006e 0061 006d        .h.e.r.e...n.a.m
0x00c0   0065 0020 003d 0020 0040 0050 0031 0020        .e...=...@.P.1..
0x00d0   0000 00e7 0001 0904 0001 0088 00cd 00cd        ................
0x00e0   00cd 00cd 00cd 00cd 00cd 00cd 00cd 00cd        ................
0x00f0   00cd 00cd 00cd 00cd 00cd 00cd 00cd 00cd        ................

As you can see, the Microsoft ODBC driver implements SQLDescribeParam()
by  parsing the SQL locally and asking the server for the datatypes of
the placeholders.  

Anybody want to break out lex & yacc and build us a parser?  

If not, I think we should document that this is basically never going to
work.

--jkl



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