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 * FROM orders WHERE id=?", orderId)
    if err != nil {
        log.Fatal(err)
    }
    log.Printf("Successfully queried and receive %d orders", orders.count)
    return orders
}

Are there any easy ways to .count the results? I'd like to keep this database engine agonistic, but FWIW.... I'm using Matt N's sqlite3 driver for my integration tests, but plan on having a different DB in prod.

SELECT count(*) FROM orders WHERE id=....

esdebon
– esdebon

2014-02-27 15:56:45 +00:00
Commented Feb 27, 2014 at 15:56 — esdebon
– esdebon, Commented Feb 27, 2014 at 15:56

Damien Tournoud · Accepted Answer · 2014-02-27 17:02:14Z

4

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.

edited Feb 27, 2014 at 17:02

answered Feb 27, 2014 at 16:50

Damien Tournoud

5962 silver badges4 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Vector · Accepted Answer · 2014-03-03 05:01:01Z

3

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.

edited Mar 3, 2014 at 5:01

answered Mar 3, 2014 at 4:52

Vector

11.9k12 gold badges65 silver badges109 bronze badges

Collectives™ on Stack Overflow

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

2 Answers 2

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related