GO：根据参数号在if else中获取各种查询结果

I am using go-mysql-driver to make queries to my database. I have a function In which I am passing id and warehouseId.

Now I am modifying my mysql query based on if warehouseId value is 0 or not.

The problem is the parameters that I pass in db.Query(). Following is my mysql query where I am appending additional query if warehouseId is not 0.

query := "select id,description from offers inner join offer_entities on offers.id = offer_entities.offer_id where offer_entities.entity_id = ?"
if warehouseId != 0 {
    query += `and offer_entities.warehouse_id = ? `
}
query += `group by offer_id`

I parse it like this:

if warehouseId != 0 {
    rows, err := db.Query(query, variantId, warehouseId)
} else {
    rows, err := db.Query(query, variantId)
}

However, the problem is when I run it, I get an error undefined: rows. I know that it is because rows should be defined outside the if-else conditions. But I don't understand how to define rows outside if-else or If there is any other way I could achieve my requirements.

How should I tackle this problem.

Thanks in advance.

the problem is because of variables are defined in the scope in which they are declared.

The difference between = and := is that = is just assignment and := is used for assignment and declaration

for example

 rows := 1 
//it basically means 
 var rows int 
 rows = 1

what you want is to declare rows outside the if-else and then use them, will solve the problem.

Scope visibility

Each block has itself visibility scope. A general rule is visible from inner, invisible from outer. It means you can see variables from superior scope in subject scope but not vise versa.

I believe you use rows declared in if statement out of the block, so it doesn't exist there.

var err error
var rows string
if warehouseId != 0 {
    rows, err := db.Query(query, variantId, warehouseId)
} else {
    rows, err := db.Query(query, variantId)
}
fmt.Println(rows) // It is now possible to use `rows` outside of the block

Declaration styles

var name <type> is a common declaration way. The variable with typed nil value will be declared.

name := <value of type> is a short declaration form. It will declare a variable of a type and assign a value to it at the same time. Allowed only in functions.