Controlla l'esistenza del set di dati
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Una funzione per verificare se esiste un set di dati.
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Per la documentazione dettagliata che include questo esempio di codice, vedi quanto segue:
Esempio di codice
Salvo quando diversamente specificato, i contenuti di questa pagina sono concessi in base alla licenza Creative Commons Attribution 4.0, mentre gli esempi di codice sono concessi in base alla licenza Apache 2.0. Per ulteriori dettagli, consulta le norme del sito di Google Developers. Java è un marchio registrato di Oracle e/o delle sue consociate.
[[["Facile da capire","easyToUnderstand","thumb-up"],["Il problema è stato risolto","solvedMyProblem","thumb-up"],["Altra","otherUp","thumb-up"]],[["Difficile da capire","hardToUnderstand","thumb-down"],["Informazioni o codice di esempio errati","incorrectInformationOrSampleCode","thumb-down"],["Mancano le informazioni o gli esempi di cui ho bisogno","missingTheInformationSamplesINeed","thumb-down"],["Problema di traduzione","translationIssue","thumb-down"],["Altra","otherDown","thumb-down"]],[],[[["\u003cp\u003eThis content provides code samples in Java and Python for checking if a dataset exists in BigQuery.\u003c/p\u003e\n"],["\u003cp\u003eThe Java code sample uses the \u003ccode\u003eBigQuery\u003c/code\u003e client library to check for a dataset's existence by name and returns whether it was found or not.\u003c/p\u003e\n"],["\u003cp\u003eThe Python code sample uses the \u003ccode\u003ebigquery\u003c/code\u003e library and handles the \u003ccode\u003eNotFound\u003c/code\u003e exception to determine whether a specified dataset is present.\u003c/p\u003e\n"],["\u003cp\u003eBoth code samples direct the user to authentication documentation to ensure proper setup using Application Default Credentials.\u003c/p\u003e\n"],["\u003cp\u003eBoth code samples are based on user defined parameters that need to be correctly setup before running.\u003c/p\u003e\n"]]],[],null,["# Check dataset existence\n\nA function to check whether a dataset exists.\n\nExplore further\n---------------\n\n\nFor detailed documentation that includes this code sample, see the following:\n\n- [Listing datasets](/bigquery/docs/listing-datasets)\n\nCode sample\n-----------\n\n### Java\n\n\nBefore trying this sample, follow the Java setup instructions in the\n[BigQuery quickstart using\nclient libraries](/bigquery/docs/quickstarts/quickstart-client-libraries).\n\n\nFor more information, see the\n[BigQuery Java API\nreference documentation](/java/docs/reference/google-cloud-bigquery/latest/overview).\n\n\nTo authenticate to BigQuery, set up Application Default Credentials.\nFor more information, see\n\n[Set up authentication for client libraries](/bigquery/docs/authentication#client-libs).\n\n import com.google.cloud.bigquery.https://cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.BigQuery.html;\n import com.google.cloud.bigquery.https://cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.BigQueryException.html;\n import com.google.cloud.bigquery.https://cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.BigQueryOptions.html;\n import com.google.cloud.bigquery.https://cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.Dataset.html;\n import com.google.cloud.bigquery.https://cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.DatasetId.html;\n\n // Sample to check dataset exist\n public class DatasetExists {\n\n public static void main(String[] args) {\n // TODO(developer): Replace these variables before running the sample.\n String datasetName = \"MY_DATASET_NAME\";\n datasetExists(datasetName);\n }\n\n public static void datasetExists(String datasetName) {\n try {\n // Initialize client that will be used to send requests. This client only needs to be created\n // once, and can be reused for multiple requests.\n https://cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.BigQuery.html bigquery = https://cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.BigQueryOptions.html.getDefaultInstance().getService();\n\n https://cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.Dataset.html dataset = bigquery.https://cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.BigQuery.html#com_google_cloud_bigquery_BigQuery_getDataset_com_google_cloud_bigquery_DatasetId_com_google_cloud_bigquery_BigQuery_DatasetOption____(DatasetId.of(datasetName));\n if (dataset != null) {\n System.out.println(\"Dataset already exists.\");\n } else {\n System.out.println(\"Dataset not found.\");\n }\n } catch (https://cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/com.google.cloud.bigquery.BigQueryException.html e) {\n System.out.println(\"Something went wrong. \\n\" + e.toString());\n }\n }\n }\n\n### Python\n\n\nBefore trying this sample, follow the Python setup instructions in the\n[BigQuery quickstart using\nclient libraries](/bigquery/docs/quickstarts/quickstart-client-libraries).\n\n\nFor more information, see the\n[BigQuery Python API\nreference documentation](/python/docs/reference/bigquery/latest).\n\n\nTo authenticate to BigQuery, set up Application Default Credentials.\nFor more information, see\n\n[Set up authentication for client libraries](/bigquery/docs/authentication#client-libs).\n\n from google.cloud import https://cloud.google.com/python/docs/reference/bigquery/latest/\n from google.cloud.exceptions import NotFound\n\n client = https://cloud.google.com/python/docs/reference/bigquery/latest/.https://cloud.google.com/python/docs/reference/bigquery/latest/google.cloud.bigquery.client.Client.html()\n\n # TODO(developer): Set dataset_id to the ID of the dataset to determine existence.\n # dataset_id = \"your-project.your_dataset\"\n\n try:\n client.https://cloud.google.com/python/docs/reference/bigquery/latest/google.cloud.bigquery.client.Client.html#google_cloud_bigquery_client_Client_get_dataset(dataset_id) # Make an API request.\n print(\"Dataset {} already exists\".format(dataset_id))\n except NotFound:\n print(\"Dataset {} is not found\".format(dataset_id))\n\nWhat's next\n-----------\n\n\nTo search and filter code samples for other Google Cloud products, see the\n[Google Cloud sample browser](/docs/samples?product=bigquery)."]]