SQL GROUP BY Syntax and Usage

Note

This feature is only available in NCache Enterprise Edition.

NCache provides you with the ability to group the data according to the given criteria thorugh SQL like query format using GROUP BY clause.

Important

Note that the GROUP BYclause cannot be used without an Aggregate function.

Pre-Requisites

• Indexing for searchable objects and their attributes need to be configured first as explained in Configuring Query Indexes in Administrator's Guide.
• Include the following namespaces in your application:
  • Alachisoft.NCache.Client
  • Alachisoft.NCache.Runtime.Caching
  • Alachisoft.NCache.Client.Services
  • Alachisoft.NCache.Runtime.Exceptions
• The application must be connected to cache before performing the operation.
• Cache must be running.
• Make sure that the data being added is serializable.
• To ensure the operation is fail safe, it is recommended to handle any potential exceptions within your application, as explained in Handling Failures.

Modern Syntax

The following example retrieves all the products with unitPrice greater than 5 and groups them according to their category. For example, the products with unitPrice greater than 5 belonging to the category Beverages will be retrieved and grouped.

try
{
    // Pre-condition: Cache is already connected
    // Items are already present in the cache

    // Specify the query with the specified criteria
    // Use the Fully Qualified Name (FQN) of your own custom class
    string query = "SELECT Category, COUNT(*) FROM Product.Products WHERE UnitPrice > 5 Group By Category";

    // Use QueryCommand for query execution
    var queryCommand = new QueryCommand(query);

    // Executing QueryCommand through ICacheReader
    ICacheReader reader = cache.SearchService.ExecuteReader(queryCommand);

    // Check if result set is not empty
    if (reader.FieldCount > 0)
    {
      while (reader.Read())
      {
        // Get the value of the result set
        int result = reader.GetValue<int>(1);
        string category = reader.GetValue<string>(0);
      }
    }
    else
    { 
      // Null query result set retrieved
    }
}
catch (OperationFailedException ex)
{
    if (ex.ErrorCode == NCacheErrorCodes.INCORRECT_FORMAT)
    {
        // Make sure that the query format is correct
    }
    else
    {
        // Exception can occur due to:
        // GROUPBY can only be used with aggregate functions
        // Same value for column cannot be selected twice
        // Connection Failures
        // Operation Timeout
        // Operation performed during state transfer
    }
}
catch (Exception ex)
{
  // Any generic exception like ArgumentException, ArgumentNullException
}

Legacy Syntax

Note

Legacy API is only available in NCache Enterprise Edition.

The following example groups the products from the cache based on the category using ExecuteReader. It retrieves all the products with unitPrice greater than 5 and groups them according to their category. For example, the products with unitPrice greater than 5 belonging to the category Beverages will be retrieved and grouped. Similarly data will be grouped based on other categories.

try
{
  // Pre-condition: Cache is already connected
  // Items are already present in the cache

  // Specify the query with the specified criteria
  // Use the Fully Qualified Name (FQN) of your own custom class
  string query = "SELECT COUNT(FQN.Product) WHERE this.UnitPrice > ? GROUP BY this.Category";

  // Use QueryCommand for query execution
  var queryCommand = new QueryCommand(query);

  // Providing parameters for query
  queryCommand.Parameters.Add("UnitPrice", 5);

  // Executing QueryCommand through ICacheReader
  ICacheReader reader = cache.ExecuteReader(queryCommand);

  // Check if result set is not empty
  if (reader.FieldCount > 0)
  {
    while (reader.Read())
    {
      // Get the value of the result set
      int result = reader.GetValue<int>(1);
      // Perform operations
    }
  }
  else
  {
    // Null query result set retrieved
  }
}
catch (OperationFailedException ex)
{
    if (ex.ErrorCode == NCacheErrorCodes.INCORRECT_FORMAT)
    {
        // Make sure that the query format is correct
    }
    else
    {
        // Exception can occur due to:
        // GROUPBY can only be used with aggregate functions
        // Same value for column cannot be selected twice
        // Connection Failures
        // Operation Timeout
        // Operation performed during state transfer
    }
}
catch (Exception ex)
{
  // Any generic exception like ArgumentException, ArgumentNullException
}

Recommendation: To ensure the operation is fail safe, it is recommended to handle any potential exceptions within your application, as explained in Handling Failures.

Additional Resources

NCache provides sample application for SQL Searching at:

• GitHub
• Shipped with NCache: %NCHOME%\samples\dotnet\SearchUsingSQL

See Also

Locking Data For Concurrency Control
SQL Search for Keys Syntax and Usage
SQL Search for Keys Syntax and Usage
SQL IN Operator Syntax and Usage
SQL Like Operator Syntax and Usage
Query Operators
Search Cache with LINQ