[]byte convert to NULL

[Terry-Mao]

When we use binary as a column type, how to insert a NULL value for the column?
code :
db.Exec("INSERT INTO t(a) VALUES(?)", a);

in my opion, when a is nil then insert a NULL value, but now insert a 0x0000...

[julienschmidt]

Which Go version are you using?

[Terry-Mao]

ENV:

GOARCH="amd64"
GOBIN=""
GOCHAR="6"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GORACE=""
GOROOT="/usr/local/go"
TERM="dumb"
CC="clang"
GOGCCFLAGS="-g -O2 -fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fno-common"
CGO_ENABLED="1"

VERSION:
go version devel +f4d1cb8d9a91 Thu Sep 19 22:34:33 2013 +1000 darwin/amd64

[julienschmidt]

Now the Version of Go-MySQL-Driver.
If the driver was installed via go get please look for the version in the README.md of your local copy,
if you cloned the repository via git, please tell us the SHA1 of the latest commit in your copy.

[Terry-Mao]

Current tagged Release: June 03, 2013 (Version 1.0.1)

[julienschmidt]

a has the type []byte?

Currently NULL is only inserted for nil values with the type interface{}:
https://github.com/go-sql-driver/mysql/blob/v1.0.1/packets.go#L725

Here is why: http://play.golang.org/p/jP9Hj6clfG
[]byte(nil) equals []byte(""), but []byte(nil) != interface{}(nil)

I know this is not intuitive. I'm open for suggestions.

Your example would work this way:

db.Exec("INSERT INTO t(a) VALUES(?)", nil);

or

var a interface{} = nil
db.Exec("INSERT INTO t(a) VALUES(?)", a);

[Terry-Mao]

@ julienschmidt thks a lot, i was shocked about this code:

var a,b []byte
a = nil
b = []byte("")
println(a, b, bytes.Equal(a, b), a == nil, b == nil)

a equals b !!!!!!! looks like a language defect..

[DisposaBoy]

@Terry-Mao that's comparing the contents of the slices. There is no content in either case...

[Terry-Mao]

now i wrote like this:

var b interface{}
if a == nil {
b = nil
}
db.Exec("INSERT INTO t(a) VALUES(?)", b);

[Terry-Mao]

@DisposaBoy
whis this can happen?

var c, d interface{}
c = nil
d = a // is []byte(nil)
println(c, d, c == d, c == nil, d == nil)

d != nil....i am puzzled..
so to the go-sql-driver ,it's hard to distinguish 0x0 and NULL

[DisposaBoy]

@Terry-Mao ofcourse d isn't nil, it's an initialized []byte because that's what a is. http://golang.org/doc/faq#nil_error explains something similar with relation to interfaces

[Terry-Mao]

@DisposaBoy thks a lot..

@julienschmidt
try to think about the :
type Null struct {
Converter ValueConverter
}

sth like NullByte

[julienschmidt]

Please take a look at pull request #147

[Terry-Mao]

@julienschmidt ok，i'll have a look at the PR.