How do I get the number of rows returned while using database/sql?

Question

Given the following function:

func (me *OrderService) GetOrders(orderTx *sql.Tx, orderId int) (orders *sql.Rows) {
    orders, err := ecommTx.Query(\"SELECT * FR         


        

Answer 1

There is no portable way to know the number of rows returned by a statement in advance, meaning without iterating through the returned cursor and counting.

There are two typical solutions to this:

• Run a separate COUNT(*) query. The problem with this approach is that it's very racy (the result set can be modified between the two queries, at least in some transaction isolation modes), so it is really only useful for things like pagers where you do a query that returns only part of the result set, and want to know how many other rows there are.

• Iterate through the cursor and count. In Go, that means calling .Next() and then .Scan the result into your Order struct.

Answer 2

sql.Query() returns *Rows. Rows is a reader, not a collection, so calls such as count() or len() etc. are not relevant. You have to read through Rows to know how many entries you've got:

count := 0
for orders.Next() {
    count++
}

log.Printf("Successfully queried and receive %d orders", count)

You are not adding any extra overhead by doing so. Other languages, such as C# or Delphi, that might return a collection with a count property are simply doing the reading for you and packaging the results into a collection for your convenience.