How to scan a sum value from a PosgreSQL database using PGX for Goland

Question

I am running into trouble getting a sum() value from a Postgres database using PGX drive for Golang.

Here is my code:. I added a second variable because the row is returning two values.

---

var cartItemPriceFloat float64 var secondVariable string

row, err := global.Db.Query(context.Background(), "select sum(shopping_cart_rows.shopping_cart_row_product_quantity * products.product_price) as cart_item_price from shopping_cart_rows inner join products on products.product_id=shopping_cart_rows.shopping_cart_row_product_id where shopping_cart_rows.shopping_cart_row_user_id=$1", userId)

if err != nil {
    fmt.Println("Error retrieving cart item price: ", err)
}

fmt.Println("The output from the query is ", row)

err2 := row.Scan(&cartItemPriceFloat, &secondVariable)
if err2 != nil {
    fmt.Println("Error scanning query result into cartItemPriceFloat: ", err2)
}
fmt.Println("cartItemPriceFloat = ", cartItemPriceFloat)
fmt.Println("secondVariable = ", secondVariable)

---

The terminal output is:

The output from the query is &{0xc0003b6000 0xc0003ac7f0 } Error scanning query result into cartItemPriceFloat: number of field descriptions must equal number of values, got 1 and 0 cartItemPriceFloat = 0 secondVariable =

---

I am probably missing something simple. All I want is the value of cartItemPriceFloat. BTW, when I run this query in the Postgres console, it returns the correct value.

Answer 1

Your query returns a single scalar, cart_item_price:

select
    sum(shopping_cart_rows.shopping_cart_row_product_quantity * products.product_price) as cart_item_price
    from shopping_cart_rows
    inner join products
        on products.product_id=shopping_cart_rows.shopping_cart_row_product_id
    where shopping_cart_rows.shopping_cart_row_user_id=$1

You must scan for only one field and one row. Use QueryRowinstead:

queryString := `
    select
        sum(shopping_cart_rows.shopping_cart_row_product_quantity * products.product_price) as cart_item_price
        from shopping_cart_rows
        inner join products
            on products.product_id=shopping_cart_rows.shopping_cart_row_product_id
        where shopping_cart_rows.shopping_cart_row_user_id=$1
`

var cartItemPriceFloat float32

global.Db.QueryRow(context.Background(), queryString, userId).Scan(&cartItemPriceFloat)

fmt.Println(cartItemPriceFloat)