we use base package to store common things for all databases. what we will do after adding one more protocol? for example mysql X or mariaDB or mssql?)
okay, we want return type aware values line Int/String/Bytes which knows how to encode value according to DBs protocol. okay, there is great place for design patterns)

we can introduce fabric that can create new Int/String/Bytes values that will implement EncodingValue with methods like EncodeToBinary/EncodeToInt:

type TypeFactory interface {
  NewBytesValue(...) EncodingValue
  NewIntValue(...) EncodingValue
  NewStringValue(...) EncodingValue
}

Then update common function EncodeDefault and accept +1 parameter func EncodeDefault(..., typeFactory TypeFactory) and use it to create new Int/String values instead of calling functions NewBytesValue that should implement methods for mysql/postgresql/etc

After that target db package should implement own fabric that will return own implementations of EncodedValue and return them.

Yeah, you are right. It was one of the possible implementations, but I thought that it has much complexity. But current implementation is hard to extend. So, good idea!

it's mysql related functions. they should be stored in mysql package, not in base)

nice)

can you explain why we expect \x in this strings? documentation tells that binary data should be sent as hex literals like X'<hex_val>' or as 0x<hex_val>. As I remember, \x<hex_val> it is postgresql specific literals

Don't forget that this is a go string :)
The first byte(s) of encoded string is a length of that string. It out case, length is 6. So, to insert a 06 byte I used escaping.
Another way of writing that is:

[]byte{06, 's', 't', 'r', 'i', 'n', 'g'}

Which, imho, is less readable

aaaaaaaa, understood. thanks for explanation. you r right

same here, why we expect \x, not 0x<hex_val>?