Change a column from required to nullable in a load append job.

## Explore further


For detailed documentation that includes this code sample, see the following:

- [Modifying table schemas](https://docs.cloud.google.com/bigquery/docs/managing-table-schemas)

## Code sample

### Go


Before trying this sample, follow the Go setup instructions in the
[BigQuery quickstart using
client libraries](https://docs.cloud.google.com/bigquery/docs/quickstarts/quickstart-client-libraries).


For more information, see the
[BigQuery Go API
reference documentation](https://godoc.org/cloud.google.com/go/bigquery).


To authenticate to BigQuery, set up Application Default Credentials.
For more information, see

[Set up authentication for client libraries](https://docs.cloud.google.com/bigquery/docs/authentication#client-libs).

    import (
    	"context"
    	"fmt"
    	"os"

    	"cloud.google.com/go/bigquery"
    )

    // relaxTableImport demonstrates amending the schema of a table to relax columns from
    // not allowing NULL values to allowing them.
    func relaxTableImport(projectID, datasetID, tableID, filename string) error {
    	// projectID := "my-project-id"
    	// datasetID := "mydataset"
    	// tableID := "mytable"
    	ctx := context.Background()
    	client, err := bigquery.NewClient(ctx, projectID)
    	if err != nil {
    		return fmt.Errorf("bigquery.NewClient: %w", err)
    	}
    	defer client.Close()

    	sampleSchema := bigquery.https://docs.cloud.google.com/go/docs/reference/cloud.google.com/go/bigquery/latest/index.html#cloud_google_com_go_bigquery_Schema{
    		{Name: "full_name", Type: bigquery.https://docs.cloud.google.com/go/docs/reference/cloud.google.com/go/bigquery/latest/index.html#cloud_google_com_go_bigquery_StringFieldType_BytesFieldType_IntegerFieldType_FloatFieldType_BooleanFieldType_TimestampFieldType_RecordFieldType_DateFieldType_TimeFieldType_DateTimeFieldType_NumericFieldType_GeographyFieldType_BigNumericFieldType_IntervalFieldType_JSONFieldType_RangeFieldType, Required: true},
    		{Name: "age", Type: bigquery.https://docs.cloud.google.com/go/docs/reference/cloud.google.com/go/bigquery/latest/index.html#cloud_google_com_go_bigquery_StringFieldType_BytesFieldType_IntegerFieldType_FloatFieldType_BooleanFieldType_TimestampFieldType_RecordFieldType_DateFieldType_TimeFieldType_DateTimeFieldType_NumericFieldType_GeographyFieldType_BigNumericFieldType_IntervalFieldType_JSONFieldType_RangeFieldType, Required: true},
    	}
    	meta := &bigquery.https://docs.cloud.google.com/go/docs/reference/cloud.google.com/go/bigquery/latest/index.html#cloud_google_com_go_bigquery_TableMetadata{
    		Schema: sampleSchema,
    	}
    	tableRef := client.Dataset(datasetID).Table(tableID)
    	if err := tableRef.Create(ctx, meta); err != nil {
    		return err
    	}
    	// Now, import data from a local file, but specify relaxation of required
    	// fields as a side effect while the data is appended.
    	f, err := os.Open(filename)
    	if err != nil {
    		return err
    	}
    	source := bigquery.https://docs.cloud.google.com/go/docs/reference/cloud.google.com/go/bigquery/latest/index.html#cloud_google_com_go_bigquery_ReaderSource_NewReaderSource(f)
    	source.AutoDetect = true   // Allow BigQuery to determine schema.
    	source.SkipLeadingRows = 1 // CSV has a single header line.

    	loader := client.Dataset(datasetID).Table(tableID).https://docs.cloud.google.com/go/docs/reference/cloud.google.com/go/bigquery/latest/index.html#cloud_google_com_go_bigquery_Table_LoaderFrom(source)
    	loader.SchemaUpdateOptions = []string{"ALLOW_FIELD_RELAXATION"}
    	job, err := loader.Run(ctx)
    	if err != nil {
    		return err
    	}
    	status, err := job.Wait(ctx)
    	if err != nil {
    		return err
    	}
    	if err := status.https://docs.cloud.google.com/go/docs/reference/cloud.google.com/go/bigquery/latest/index.html#cloud_google_com_go_bigquery_JobStatus_Err(); err != nil {
    		return err
    	}
    	return nil
    }

### Java


Before trying this sample, follow the Java setup instructions in the
[BigQuery quickstart using
client libraries](https://docs.cloud.google.com/bigquery/docs/quickstarts/quickstart-client-libraries).


For more information, see the
[BigQuery Java API
reference documentation](https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/overview).


To authenticate to BigQuery, set up Application Default Credentials.
For more information, see

[Set up authentication for client libraries](https://docs.cloud.google.com/bigquery/docs/authentication#client-libs).

    import com.google.cloud.bigquery.https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.BigQuery.html;
    import com.google.cloud.bigquery.https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.BigQueryException.html;
    import com.google.cloud.bigquery.https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.BigQueryOptions.html;
    import com.google.cloud.bigquery.https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.CsvOptions.html;
    import com.google.cloud.bigquery.https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.Field.html;
    import com.google.cloud.bigquery.https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.Job.html;
    import com.google.cloud.bigquery.https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.JobInfo.html;
    import com.google.cloud.bigquery.https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.LoadJobConfiguration.html;
    import com.google.cloud.bigquery.https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.Schema.html;
    import com.google.cloud.bigquery.https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.StandardSQLTypeName.html;
    import com.google.cloud.bigquery.https://docs.cloud.google.com/java/docs/reference/google-cloud-biglake/latest/com.google.cloud.bigquery.biglake.v1.Table.html;
    import com.google.cloud.bigquery.https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.TableId.html;
    import com.google.common.collect.ImmutableList;

    // Sample to append relax column in a table.
    public class RelaxColumnLoadAppend {

      public static void main(String[] args) {
        // TODO(developer): Replace these variables before running the sample.
        String datasetName = "MY_DATASET_NAME";
        String tableName = "MY_TABLE_NAME";
        String sourceUri = "gs://cloud-samples-data/bigquery/us-states/us-states.csv";
        relaxColumnLoadAppend(datasetName, tableName, sourceUri);
      }

      public static void relaxColumnLoadAppend(String datasetName, String tableName, String sourceUri) {
        try {
          // Initialize client that will be used to send requests. This client only needs to be created
          // once, and can be reused for multiple requests.
          https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.BigQuery.html bigquery = https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.BigQueryOptions.html.getDefaultInstance().getService();

          // Retrieve destination table reference
          https://docs.cloud.google.com/java/docs/reference/google-cloud-biglake/latest/com.google.cloud.bigquery.biglake.v1.Table.html table = bigquery.https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.BigQuery.html#com_google_cloud_bigquery_BigQuery_getTable_com_google_cloud_bigquery_TableId_com_google_cloud_bigquery_BigQuery_TableOption____(TableId.of(datasetName, tableName));

          // column as a 'REQUIRED' field.
          https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.Field.html name =
              https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.Field.html.newBuilder("name", https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.StandardSQLTypeName.html.STRING).setMode(https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.Field.html.Mode.REQUIRED).build();
          https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.Field.html postAbbr =
              https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.Field.html.newBuilder("post_abbr", https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.StandardSQLTypeName.html.STRING)
                  .setMode(https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.Field.html.Mode.REQUIRED)
                  .build();
          https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.Schema.html schema = https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.Schema.html.of(name, postAbbr);

          // Skip header row in the file.
          https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.CsvOptions.html csvOptions = https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.CsvOptions.html.newBuilder().setSkipLeadingRows(1).build();

          // Set job options
          https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.LoadJobConfiguration.html loadConfig =
              https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.LoadJobConfiguration.html.newBuilder(table.getTableId(), sourceUri)
                  .setSchema(schema)
                  .setFormatOptions(csvOptions)
                  .setSchemaUpdateOptions(
                      ImmutableList.of(https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.JobInfo.html.SchemaUpdateOption.ALLOW_FIELD_RELAXATION))
                  .setWriteDisposition(https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.JobInfo.html.WriteDisposition.WRITE_APPEND)
                  .build();

          // Create a load job and wait for it to complete.
          https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.Job.html job = bigquery.https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.BigQuery.html#com_google_cloud_bigquery_BigQuery_create_com_google_cloud_bigquery_DatasetInfo_com_google_cloud_bigquery_BigQuery_DatasetOption____(JobInfo.of(loadConfig));
          job = job.https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.Job.html#com_google_cloud_bigquery_Job_waitFor_com_google_cloud_bigquery_BigQueryRetryConfig_com_google_cloud_RetryOption____();
          // Check the job's status for errors
          if (job.https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.Job.html#com_google_cloud_bigquery_Job_isDone__() && job.getStatus().getError() == null) {
            System.out.println("Relax column append successfully loaded in a table");
          } else {
            System.out.println(
                "BigQuery was unable to load into the table due to an error:"
                    + job.getStatus().getError());
          }
        } catch (https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.BigQueryException.html | InterruptedException e) {
          System.out.println("Column not added during load append \n" + e.toString());
        }
      }
    }

### Python


Before trying this sample, follow the Python setup instructions in the
[BigQuery quickstart using
client libraries](https://docs.cloud.google.com/bigquery/docs/quickstarts/quickstart-client-libraries).


For more information, see the
[BigQuery Python API
reference documentation](https://docs.cloud.google.com/python/docs/reference/bigquery/latest).


To authenticate to BigQuery, set up Application Default Credentials.
For more information, see

[Set up authentication for client libraries](https://docs.cloud.google.com/bigquery/docs/authentication#client-libs).

    # from google.cloud import bigquery
    # client = bigquery.Client()
    # project = client.project
    # dataset_ref = bigquery.DatasetReference(project, 'my_dataset')
    # filepath = 'path/to/your_file.csv'

    # Retrieves the destination table and checks the number of required fields
    table_id = "my_table"
    table_ref = dataset_ref.table(table_id)
    table = client.get_table(table_ref)
    original_required_fields = sum(field.mode == "REQUIRED" for field in table.schema)
    # In this example, the existing table has 3 required fields.
    print("{} fields in the schema are required.".format(original_required_fields))

    # Configures the load job to append the data to a destination table,
    # allowing field relaxation
    job_config = bigquery.LoadJobConfig()
    job_config.write_disposition = bigquery.WriteDisposition.WRITE_APPEND
    job_config.schema_update_options = [
        bigquery.SchemaUpdateOption.ALLOW_FIELD_RELAXATION
    ]
    # In this example, the existing table contains three required fields
    # ('full_name', 'age', and 'favorite_color'), while the data to load
    # contains only the first two fields.
    job_config.schema = [
        bigquery.SchemaField("full_name", "STRING", mode="REQUIRED"),
        bigquery.SchemaField("age", "INTEGER", mode="REQUIRED"),
    ]
    job_config.source_format = bigquery.SourceFormat.CSV
    job_config.skip_leading_rows = 1

    with open(filepath, "rb") as source_file:
        job = client.load_table_from_file(
            source_file,
            table_ref,
            location="US",  # Must match the destination dataset location.
            job_config=job_config,
        )  # API request

    job.result()  # Waits for table load to complete.
    print(
        "Loaded {} rows into {}:{}.".format(
            job.output_rows, dataset_id, table_ref.table_id
        )
    )

    # Checks the updated number of required fields
    table = client.get_table(table)
    current_required_fields = sum(field.mode == "REQUIRED" for field in table.schema)
    print("{} fields in the schema are now required.".format(current_required_fields))

## What's next


To search and filter code samples for other Google Cloud products, see the
[Google Cloud sample browser](https://docs.cloud.google.com/docs/samples?product=bigquery).