You have not stated whether you are sending your transactions while connected to the blockchain via geth (on-blockchain), or whether you are crafting your transaction while not connected to the blockchain (off-blockchain).
The answer by Paul S is referring to the off-blockchain crafting of transaction where you have to specify a nonce in the raw transactions you are then executing on the blockchain.
If you are sending your transaction on-blockchain, you can use the eth.sendTransaction(...) without a nonce.
For example, here are 3 transactions from the same "from" account to the same "to" account. There is no need to specify a nonce as it is automatically generated:
> eth.sendTransaction({from: '0x5e83b635f96da0752f991f0ebddc31249f452dea', to: '0x68acc3a13441b69016560d23e134c7931bbb27bb', value: web3.toWei(1, "ether")});
"0x92d6d2285b198b6b5cf80eca6d4292c9675fb53f47f786063df600d3be06dd09"
> eth.sendTransaction({from: '0x5e83b635f96da0752f991f0ebddc31249f452dea', to: '0x68acc3a13441b69016560d23e134c7931bbb27bb', value: web3.toWei(2, "ether")});
"0x0c1280c8b2f38aec032494913c1d0e65edd511fcd15e2424483f9bbf51c7172e"
> eth.sendTransaction({from: '0x5e83b635f96da0752f991f0ebddc31249f452dea', to: '0x68acc3a13441b69016560d23e134c7931bbb27bb', value: web3.toWei(3, "ether")});
"0x8b6998eea8b343a0f754cf2732a1f28caac3acdfbe97cca69f244f0614ea546a"
> eth.getTransaction("0x92d6d2285b198b6b5cf80eca6d4292c9675fb53f47f786063df600d3be06dd09");
{
blockHash: "0x8456088424a4cacd8b394b4e11732e3c96ca77ab4a999c6ba62b38ab61116b58",
blockNumber: 225,
from: "0x5e83b635f96da0752f991f0ebddc31249f452dea",
gas: 90000,
gasPrice: 20000000000,
hash: "0x92d6d2285b198b6b5cf80eca6d4292c9675fb53f47f786063df600d3be06dd09",
input: "0x",
nonce: 0,
to: "0x68acc3a13441b69016560d23e134c7931bbb27bb",
transactionIndex: 0,
value: 1000000000000000000
}
> eth.getTransaction("0x0c1280c8b2f38aec032494913c1d0e65edd511fcd15e2424483f9bbf51c7172e");
{
blockHash: "0x8456088424a4cacd8b394b4e11732e3c96ca77ab4a999c6ba62b38ab61116b58",
blockNumber: 225,
from: "0x5e83b635f96da0752f991f0ebddc31249f452dea",
gas: 90000,
gasPrice: 20000000000,
hash: "0x0c1280c8b2f38aec032494913c1d0e65edd511fcd15e2424483f9bbf51c7172e",
input: "0x",
nonce: 1,
to: "0x68acc3a13441b69016560d23e134c7931bbb27bb",
transactionIndex: 1,
value: 2000000000000000000
}
> eth.getTransaction("0x8b6998eea8b343a0f754cf2732a1f28caac3acdfbe97cca69f244f0614ea546a");
{
blockHash: "0x8456088424a4cacd8b394b4e11732e3c96ca77ab4a999c6ba62b38ab61116b58",
blockNumber: 225,
from: "0x5e83b635f96da0752f991f0ebddc31249f452dea",
gas: 90000,
gasPrice: 20000000000,
hash: "0x8b6998eea8b343a0f754cf2732a1f28caac3acdfbe97cca69f244f0614ea546a",
input: "0x",
nonce: 2,
to: "0x68acc3a13441b69016560d23e134c7931bbb27bb",
transactionIndex: 2,
value: 3000000000000000000
}
Best Answer
No. It indicates that you cannot send two transaction with the same nonce from the same address.
Yes.
I think (if someone could confirme or correct) it is the first one that gets mined. But I'm not sure at all because that miners' configuration migth have an influence on that.
From @Зелёный in the comments, you could set an higher gas price in one of yoru transaction so that it is processed before the other one. You then don't have to worry about nonce anymore.