Query sui dati con timestamp di commit

Esegui una query sui dati di una tabella contenente una colonna per il commit TIMESTAMP.

Per saperne di più

Per la documentazione dettagliata che include questo esempio di codice, vedi quanto segue:

• Timestamp dei commit nei database dialetto SQL standard di Google
• Timestamp dei commit nei database in dialetto PostgreSQL

Esempio di codice

C++

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta la pagina relativa alle librerie client di Spanner.

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void QueryDataWithTimestamp(google::cloud::spanner::Client client) {
  namespace spanner = ::google::cloud::spanner;

  spanner::SqlStatement select(
      "SELECT SingerId, AlbumId, MarketingBudget, LastUpdateTime"
      "  FROM Albums"
      " ORDER BY LastUpdateTime DESC");
  using RowType =
      std::tuple<std::int64_t, std::int64_t, absl::optional<std::int64_t>,
                 absl::optional<spanner::Timestamp>>;

  auto rows = client.ExecuteQuery(std::move(select));
  for (auto& row : spanner::StreamOf<RowType>(rows)) {
    if (!row) throw std::move(row).status();
    std::cout << std::get<0>(*row) << " " << std::get<1>(*row);
    auto marketing_budget = std::get<2>(*row);
    if (!marketing_budget) {
      std::cout << " NULL";
    } else {
      std::cout << ' ' << *marketing_budget;
    }
    auto last_update_time = std::get<3>(*row);
    if (!last_update_time) {
      std::cout << " NULL";
    } else {
      std::cout << ' ' << *last_update_time;
    }
    std::cout << "\n";
  }
}

C#

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta la pagina relativa alle librerie client di Spanner.

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using Google.Cloud.Spanner.Data;
using System;
using System.Collections.Generic;
using System.Threading.Tasks;

public class QueryDataWithTimestampColumnAsyncSample
{
    public class Album
    {
        public int SingerId { get; set; }
        public int AlbumId { get; set; }
        public DateTime? LastUpdateTime { get; set; }
        public long? MarketingBudget { get; set; }
    }

    public async Task<List<Album>> QueryDataWithTimestampColumnAsync(string projectId, string instanceId, string databaseId)
    {
        string connectionString = $"Data Source=projects/{projectId}/instances/{instanceId}/databases/{databaseId}";

        using var connection = new SpannerConnection(connectionString);
        using var cmd = connection.CreateSelectCommand("SELECT SingerId, AlbumId, MarketingBudget, LastUpdateTime FROM Albums ORDER BY LastUpdateTime DESC");

        var albums = new List<Album>();
        using var reader = await cmd.ExecuteReaderAsync();
        while (await reader.ReadAsync())
        {
            albums.Add(new Album
            {
                SingerId = reader.GetFieldValue<int>("SingerId"),
                AlbumId = reader.GetFieldValue<int>("AlbumId"),
                LastUpdateTime = reader.IsDBNull(reader.GetOrdinal("LastUpdateTime")) ? (DateTime?)null : reader.GetFieldValue<DateTime>("LastUpdateTime"),
                MarketingBudget = reader.IsDBNull(reader.GetOrdinal("MarketingBudget")) ? 0 : reader.GetFieldValue<long>("MarketingBudget")
            });
        }
        return albums;
    }
}

Go

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta la pagina relativa alle librerie client di Spanner.

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import (
	"context"
	"fmt"
	"io"
	"strconv"

	"cloud.google.com/go/spanner"
	"google.golang.org/api/iterator"
)

func queryWithTimestamp(w io.Writer, db string) error {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, db)
	if err != nil {
		return err
	}
	defer client.Close()

	stmt := spanner.Statement{
		SQL: `SELECT SingerId, AlbumId, MarketingBudget, LastUpdateTime
				FROM Albums ORDER BY LastUpdateTime DESC`}
	iter := client.Single().Query(ctx, stmt)
	defer iter.Stop()
	for {
		row, err := iter.Next()
		if err == iterator.Done {
			return nil
		}
		if err != nil {
			return err
		}
		var singerID, albumID int64
		var marketingBudget spanner.NullInt64
		var lastUpdateTime spanner.NullTime
		if err := row.ColumnByName("SingerId", &singerID); err != nil {
			return err
		}
		if err := row.ColumnByName("AlbumId", &albumID); err != nil {
			return err
		}
		if err := row.ColumnByName("MarketingBudget", &marketingBudget); err != nil {
			return err
		}
		budget := "NULL"
		if marketingBudget.Valid {
			budget = strconv.FormatInt(marketingBudget.Int64, 10)
		}
		if err := row.ColumnByName("LastUpdateTime", &lastUpdateTime); err != nil {
			return err
		}
		timestamp := "NULL"
		if lastUpdateTime.Valid {
			timestamp = lastUpdateTime.String()
		}
		fmt.Fprintf(w, "%d %d %s %s\n", singerID, albumID, budget, timestamp)
	}
}

Java

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta la pagina relativa alle librerie client di Spanner.

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static void queryMarketingBudgetWithTimestamp(DatabaseClient dbClient) {
  // Rows without an explicit value for MarketingBudget will have a MarketingBudget equal to
  // null. A try-with-resource block is used to automatically release resources held by
  // ResultSet.
  try (ResultSet resultSet =
      dbClient
          .singleUse()
          .executeQuery(
              Statement.of(
                  "SELECT SingerId, AlbumId, MarketingBudget, LastUpdateTime FROM Albums"
                      + " ORDER BY LastUpdateTime DESC"))) {
    while (resultSet.next()) {
      System.out.printf(
          "%d %d %s %s\n",
          resultSet.getLong("SingerId"),
          resultSet.getLong("AlbumId"),
          // We check that the value is non null. ResultSet getters can only be used to retrieve
          // non null values.
          resultSet.isNull("MarketingBudget") ? "NULL" : resultSet.getLong("MarketingBudget"),
          resultSet.isNull("LastUpdateTime") ? "NULL" : resultSet.getTimestamp("LastUpdateTime"));
    }
  }
}

Node.js

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta la pagina relativa alle librerie client di Spanner.

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// ...

// Imports the Google Cloud client library
const {Spanner} = require('@google-cloud/spanner');

/**
 * TODO(developer): Uncomment the following lines before running the sample.
 */
// const projectId = 'my-project-id';
// const instanceId = 'my-instance';
// const databaseId = 'my-database';

// Creates a client
const spanner = new Spanner({
  projectId: projectId,
});

// Gets a reference to a Cloud Spanner instance and database
const instance = spanner.instance(instanceId);
const database = instance.database(databaseId);

const query = {
  sql: `SELECT SingerId, AlbumId, MarketingBudget, LastUpdateTime
          FROM Albums ORDER BY LastUpdateTime DESC`,
};

// Queries rows from the Albums table
try {
  const [rows] = await database.run(query);

  rows.forEach(row => {
    const json = row.toJSON();

    console.log(
      `SingerId: ${json.SingerId}, AlbumId: ${
        json.AlbumId
      }, MarketingBudget: ${
        json.MarketingBudget ? json.MarketingBudget : null
      }, LastUpdateTime: ${json.LastUpdateTime}`
    );
  });
} catch (err) {
  console.error('ERROR:', err);
} finally {
  // Close the database when finished
  database.close();
}

PHP

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta la pagina relativa alle librerie client di Spanner.

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use Google\Cloud\Spanner\SpannerClient;

/**
 * Queries sample data from a database with a commit timestamp column.
 *
 * This sample uses the `MarketingBudget` column. You can add the column
 * by running the `add_column` sample or by running this DDL statement against
 * your database:
 *
 *      ALTER TABLE Albums ADD COLUMN MarketingBudget INT64
 *
 * This sample also uses the 'LastUpdateTime' commit timestamp column. You can
 * add the column by running the `add_timestamp_column` sample or by running
 * this DDL statement against your database:
 *
 * 		ALTER TABLE Albums ADD COLUMN LastUpdateTime TIMESTAMP OPTIONS (allow_commit_timestamp=true)
 *
 * Example:
 * ```
 * query_data_with_timestamp_column($instanceId, $databaseId);
 * ```
 *
 * @param string $instanceId The Spanner instance ID.
 * @param string $databaseId The Spanner database ID.
 */
function query_data_with_timestamp_column(string $instanceId, string $databaseId): void
{
    $spanner = new SpannerClient();
    $instance = $spanner->instance($instanceId);
    $database = $instance->database($databaseId);

    $results = $database->execute(
        'SELECT SingerId, AlbumId, MarketingBudget, LastUpdateTime ' .
        ' FROM Albums ORDER BY LastUpdateTime DESC'
    );

    foreach ($results as $row) {
        if ($row['MarketingBudget'] == null) {
            $row['MarketingBudget'] = 'NULL';
        }
        if ($row['LastUpdateTime'] == null) {
            $row['LastUpdateTime'] = 'NULL';
        }
        printf('SingerId: %s, AlbumId: %s, MarketingBudget: %s, LastUpdateTime: %s' . PHP_EOL,
            $row['SingerId'], $row['AlbumId'], $row['MarketingBudget'], $row['LastUpdateTime']);
    }
}

Python

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta la pagina relativa alle librerie client di Spanner.

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def query_data_with_timestamp(instance_id, database_id):
    """Queries sample data from the database using SQL.

    This updates the `LastUpdateTime` column which must be created before
    running this sample. You can add the column by running the
    `add_timestamp_column` sample or by running this DDL statement
    against your database:

        ALTER TABLE Performances ADD COLUMN LastUpdateTime TIMESTAMP
        OPTIONS (allow_commit_timestamp=true)

    """
    spanner_client = spanner.Client()
    instance = spanner_client.instance(instance_id)

    database = instance.database(database_id)

    with database.snapshot() as snapshot:
        results = snapshot.execute_sql(
            "SELECT SingerId, AlbumId, MarketingBudget FROM Albums "
            "ORDER BY LastUpdateTime DESC"
        )

    for row in results:
        print("SingerId: {}, AlbumId: {}, MarketingBudget: {}".format(*row))

Ruby

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta la pagina relativa alle librerie client di Spanner.

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# project_id  = "Your Google Cloud project ID"
# instance_id = "Your Spanner instance ID"
# database_id = "Your Spanner database ID"

require "google/cloud/spanner"

spanner = Google::Cloud::Spanner.new project: project_id
client  = spanner.client instance_id, database_id

client.execute("SELECT SingerId, AlbumId, MarketingBudget, LastUpdateTime
                FROM Albums ORDER BY LastUpdateTime DESC").rows.each do |row|
  puts "#{row[:SingerId]} #{row[:AlbumId]} #{row[:MarketingBudget]} #{row[:LastUpdateTime]}"
end

Passaggi successivi

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