How to tell SQL returns empty result

[Tong Sun]

Hi,

A typical GO SQL query snip looks like this:

1. rows, _ := db.Query("SELECT id, name FROM users;")
2. for rows.Next() {
3. rows.Scan(&user)
4. }

However,  how can I tell if the SQL query returns empty results?

Thanks

[Jesse McNelis]

You can count them.

i := 0

for rows.Next(){

  i++

  err := rows.Scan(&user)

  //handle error and process user

}

if i == 0 {

  //there were zero rows

}

--
=====================
http://jessta.id.au

[Tong Sun]

On Thu, Nov 14, 2013 at 8:18 PM, Jesse McNelis <jes...@jessta.id.au> wrote:

However,  how can I tell if the SQL query returns empty results?

You can count them.

That was my backup plan. Was hoping for something more elegant...

Thanks anyway.

[Julien Schmidt]

It depends on how many rows you want:

If you are only interested in if there is a result, you should do this with SQL in the query and not with client code.

If you only want 1 row or no result, you could use QueryRow:

if err := db.QueryRow("SELECT id, name FROM users").Scan(&user); err == nil {

     // 1 row

} else if err == sql.ErrNoRows {

     // empty result

} else {

     // error

}

If you want multiple rows, you could do something like this (but nor really more elegant):

rows, err := db.Query("SELECT id, name FROM users")

if err != nil {

     // error

}

if rows.Next() {

     // first row

     rows.Scan(&user)

     ...

} else {

     // empty result

}

for rows.Next() {

     // additional rows

     rows.Scan(&user)

}

[Julien Schmidt]

Or a slightly cleaner variant for multiple rows:

rows, err := db.Query("SELECT id, name FROM users")

if err != nil {

     // error

}

if rows.Next() {

     // first row

     rows.Scan(&user)

     ...

     // additional rows

     for rows.Next() {

         rows.Scan(&user)

         ...

     }

} else {

     // empty result

}

[Tong Sun]

On Fri, Nov 15, 2013 at 12:59 PM, Julien Schmidt <g...@julienschmidt.com> wrote:

Or a slightly cleaner variant for multiple rows:

Super! Thanks!