Relax a column in a query append job

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

Explore further

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

• Modifying table schemas

Code sample

Go

Before trying this sample, follow the Go setup instructions in the BigQuery quickstart using client libraries. For more information, see the BigQuery Go API reference documentation.

To authenticate to BigQuery, set up Application Default Credentials. For more information, see Set up authentication for client libraries.

import (
	"context"
	"fmt"

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

// relaxTableQuery demonstrates relaxing the schema of a table by appending query results to
// enable the table to allow NULL values.
func relaxTableQuery(projectID, datasetID, tableID 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.Schema{
		{Name: "full_name", Type: bigquery.StringFieldType, Required: true},
		{Name: "age", Type: bigquery.IntegerFieldType, Required: true},
	}
	meta := &bigquery.TableMetadata{
		Schema: sampleSchema,
	}
	tableRef := client.Dataset(datasetID).Table(tableID)
	if err := tableRef.Create(ctx, meta); err != nil {
		return err
	}
	// Now, append a query result that includes nulls, but allow the job to relax
	// all required columns.
	q := client.Query("SELECT \"Beyonce\" as full_name")
	q.QueryConfig.Dst = client.Dataset(datasetID).Table(tableID)
	q.SchemaUpdateOptions = []string{"ALLOW_FIELD_RELAXATION"}
	q.WriteDisposition = bigquery.WriteAppend
	q.Location = "US"
	job, err := q.Run(ctx)
	if err != nil {
		return err
	}
	_, err = job.Wait(ctx)
	if err != nil {
		return err
	}
	return nil
}

Java

Before trying this sample, follow the Java setup instructions in the BigQuery quickstart using client libraries. For more information, see the BigQuery Java API reference documentation.

To authenticate to BigQuery, set up Application Default Credentials. For more information, see Set up authentication for client libraries.

import com.google.cloud.bigquery.BigQuery;
import com.google.cloud.bigquery.BigQueryException;
import com.google.cloud.bigquery.BigQueryOptions;
import com.google.cloud.bigquery.Job;
import com.google.cloud.bigquery.JobInfo;
import com.google.cloud.bigquery.JobInfo.SchemaUpdateOption;
import com.google.cloud.bigquery.JobInfo.WriteDisposition;
import com.google.cloud.bigquery.QueryJobConfiguration;
import com.google.cloud.bigquery.TableId;
import com.google.cloud.bigquery.TableResult;
import com.google.common.collect.ImmutableList;

public class RelaxTableQuery {

  public static void main(String[] args) throws Exception {
    // TODO(developer): Replace these variables before running the sample.
    String projectId = "MY_PROJECT_ID";
    String datasetName = "MY_DATASET_NAME";
    String tableName = "MY_TABLE_NAME";
    relaxTableQuery(projectId, datasetName, tableName);
  }

  // To relax all columns in a destination table when you append data to it during a query job
  public static void relaxTableQuery(String projectId, String datasetName, String tableName)
      throws Exception {
    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.
      BigQuery bigquery = BigQueryOptions.getDefaultInstance().getService();

      TableId tableId = TableId.of(datasetName, tableName);

      String sourceTable = "`" + projectId + "." + datasetName + "." + tableName + "`";
      String query = "SELECT word FROM " + sourceTable + " WHERE word like '%is%'";

      QueryJobConfiguration queryConfig =
          QueryJobConfiguration.newBuilder(query)
              // Use standard SQL syntax for queries.
              // See: https://cloud.google.com/bigquery/sql-reference/
              .setUseLegacySql(false)
              .setSchemaUpdateOptions(ImmutableList.of(SchemaUpdateOption.ALLOW_FIELD_RELAXATION))
              .setWriteDisposition(WriteDisposition.WRITE_APPEND)
              .setDestinationTable(tableId)
              .build();

      Job queryJob = bigquery.create(JobInfo.newBuilder(queryConfig).build());

      queryJob = queryJob.waitFor();

      // Check for errors
      if (queryJob == null) {
        throw new Exception("Job no longer exists");
      } else if (queryJob.getStatus().getError() != null) {
        // You can also look at queryJob.getStatus().getExecutionErrors() for all
        // errors, not just the latest one.
        throw new Exception(queryJob.getStatus().getError().toString());
      }

      // Get the results.
      TableResult results = queryJob.getQueryResults();

      // Print all pages of the results.
      results
          .iterateAll()
          .forEach(
              rows -> {
                rows.forEach(row -> System.out.println("row: " + row.toString()));
              });

      System.out.println("Successfully relaxed all columns in destination table during query job");
    } catch (BigQueryException | InterruptedException e) {
      System.out.println("Columns not relaxed during query job \n" + e.toString());
    }
  }
}

What's next

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