Create ADLS External Tables in Azure Synapse

Create a Master Key if not present.

Why?
- If a database scoped credential is used, Synapse requires encryption.
- The Master Key ensures that credentials are securely stored.

✅ Needed only once per database.
✅ Required for setting up authentication.

    CREATE MASTER KEY ENCRYPTION BY PASSWORD = 'Password';

Add a storage account key or SAS token or Managed Identity.

Why?
- Uses the Access Key of the Storage Account.
- Requires adding the Access Key in the CREDENTIAL.

    CREATE DATABASE SCOPED CREDENTIAL BlobStorageCredential
    WITH IDENTITY = 'Storage Account Key',  
    SECRET = 'ddfgyhjuKG1Mr6SgtfvfvtbvfdmJ=';

Create a external data source. Path should be abfss only.

Why?
- Defines where Synapse should look for the data.
- Maps Synapse to Azure Blob Storage.
- Uses the credential for authentication.

✅ Links Synapse to your Blob Storage.
✅ Required before creating external tables.

    DROP EXTERNAL DATA SOURCE [AzureDataLakeStore]
    GO

    CREATE EXTERNAL DATA SOURCE [AzureDataLakeStore] WITH (
    LOCATION = N'abfss://ext-test@abcpoc.dfs.core.windows.net',
    CREDENTIAL = BlobStorageCredential
    )
    GO

Create external file format.

Why?
- Tells Synapse how to read the files (CSV, Parquet, JSON, Avro).
- Each format has different structures and metadata handling.
- Without this step, Synapse doesn’t know how to interpret the file.

    -- Create external file format Parquet
    CREATE EXTERNAL FILE FORMAT ParquetFileFormat
    WITH (
        FORMAT_TYPE = PARQUET
    );


    -- Create external file format CSV
    CREATE EXTERNAL FILE FORMAT CSVFormat
    WITH (  
        FORMAT_TYPE = DELIMITEDTEXT,  
        FORMAT_OPTIONS (FIELD_TERMINATOR = ';', FIRST_ROW = 1)  
    );

Create external table.

Why?
- External tables map to Blob Storage files but do not store data in Synapse.
- Queries run directly on storage, avoiding unnecessary data movement.

    CREATE EXTERNAL TABLE dbo.names_parquet
    ( 
    column0 varchar(255) NULL, 
    column1 varchar(255) NULL 
    ) 
    WITH ( 
    LOCATION = '/parquet/', 
    DATA_SOURCE = AzureDataLakeStore,
    FILE_FORMAT = ParquetFileFormat
    ) GO