BigQuery - Package cloud.google.com/go/bigquery (v1.70.0)

Package bigquery provides a client for the BigQuery service.

The following assumes a basic familiarity with BigQuery concepts. See https://cloud.google.com/bigquery/docs.

See https://godoc.org/cloud.google.com/go for authentication, timeouts, connection pooling and similar aspects of this package.

Creating a Client

To start working with this package, create a client with NewClient:

ctx := context.Background()
client, err := bigquery.NewClient(ctx, projectID)
if err != nil {
    // TODO: Handle error.
}

Querying

To query existing tables, create a Client.Query and call its Query.Read method, which starts the query and waits for it to complete:

q := client.Query(`
    SELECT year, SUM(number) as num
    FROM bigquery-public-data.usa_names.usa_1910_2013
    WHERE name = @name
    GROUP BY year
    ORDER BY year
`)
q.Parameters = []bigquery.QueryParameter{
    {Name: "name", Value: "William"},
}
it, err := q.Read(ctx)
if err != nil {
    // TODO: Handle error.
}

Then iterate through the resulting rows. You can store a row using anything that implements the ValueLoader interface, or with a slice or map of Value. A slice is simplest:

for {
    var values []bigquery.Value
    err := it.Next(&values)
    if err == iterator.Done {
        break
    }
    if err != nil {
        // TODO: Handle error.
    }
    fmt.Println(values)
}

You can also use a struct whose exported fields match the query:

type Count struct {
    Year int
    Num  int
}
for {
    var c Count
    err := it.Next(&c)
    if err == iterator.Done {
        break
    }
    if err != nil {
        // TODO: Handle error.
    }
    fmt.Println(c)
}

You can also start the query running and get the results later. Create the query as above, but call Query.Run instead of Query.Read. This returns a Job, which represents an asynchronous operation.

job, err := q.Run(ctx)
if err != nil {
    // TODO: Handle error.
}

Get the job's ID, a printable string. You can save this string to retrieve the results at a later time, even in another process.

jobID := job.ID()
fmt.Printf("The job ID is %s\n", jobID)

To retrieve the job's results from the ID, first look up the Job with the Client.JobFromID method:

job, err = client.JobFromID(ctx, jobID)
if err != nil {
    // TODO: Handle error.
}

Use the Job.Read method to obtain an iterator, and loop over the rows. Calling Query.Read is preferred for queries with a relatively small result set, as it will call BigQuery jobs.query API for a optimized query path. If the query doesn't meet that criteria, the method will just combine Query.Run and Job.Read.

it, err = job.Read(ctx)
if err != nil {
    // TODO: Handle error.
}
// Proceed with iteration as above.

Datasets and Tables

You can refer to datasets in the client's project with the Client.Dataset method, and in other projects with the Client.DatasetInProject method:

myDataset := client.Dataset("my_dataset")
yourDataset := client.DatasetInProject("your-project-id", "your_dataset")

These methods create references to datasets, not the datasets themselves. You can have a dataset reference even if the dataset doesn't exist yet. Use