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

Install the following NuGet packages:
- Alachisoft.NCache.SDK.
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.
For API details, refer to: ICache, ICacheReader, ExecuteReader, SearchService, QueryCommand.
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.
To handle any unseen exceptions, refer to the Troubleshooting section.

Add the following Maven dependencies in your pom.xml file:

<dependency>
    <groupId>com.alachisoft.ncache</groupId>
    <artifactId>ncache-client</artifactId>
    <version>5.2.0</version>
</dependency>

Indexing for searchable objects and their attributes need to be configured first as explained in Configuring Query Indexes in Administrator's Guide.
Import the following packages in your application:
- import com.alachisoft.ncache.client.*;
- import com.alachisoft.ncache.runtime.exceptions.*;
The application must be connected to cache before performing the operation.
Cache must be running.
For API details, refer to: Cache, CacheReader, executeReader, getSearchService(), QueryCommand.
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.
To handle any unseen exceptions, refer to the Troubleshooting section.

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 modules in your application.
- const ncache = require('ncache-client')
The application must be connected to cache before performing the operation.
Cache must be running.
For API details, refer to: Cache, CacheReader, executeReader, getSearchService(), QueryCommand.
To ensure the operation is fail safe, it is recommended to handle any potential exceptions within your application, as explained in Handling Failures.
To handle any unseen exceptions, refer to the Troubleshooting section.

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
}

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 FQN.Product WHERE UnitPrice > 5 Group By Category";

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

    // Executing QueryCommand through CacheReader
    CacheReader reader = cache.getSearchService().executeReader(queryCommand);

    // Check if result set is not empty
        if (reader.getFieldCount() > 0)
        {
            while (reader.read())
            {
                // Get the value of the result set
                int result = reader.getValue(1, Integer.class);
                String category = reader.getValue(0, String.class);
            }
        }
        else 
        {
            // Null query result set retrieved
        }

        }
catch (OperationFailedException ex)
{
    if (ex.getErrorCode() == NCacheErrorCodes.INCORRECT_FORMAT)
    {
        // Make sure the query format is correct
    }
    else
    {
        // Exception can occur due to:
        // Connection Failures
        // Operation Timeout
        // Operation performed during state transfer
    }

}
catch (Exception ex)
{
    // Any generic exception like IllegalArgumentException or NullPointerException
}

// This is an async method
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
    var query = "SELECT Category, COUNT(*) FROM FQN.Product WHERE UnitPrice > 5 Group By Category"; 

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

    // Executing QueryCommand through CacheReader
    var searchService = await this.cache.getSearchService();
    var reader = await searchService.executeReader(queryCommand);

    // Check if result set is not empty
    if (reader.getFieldCount() > 0)
    {
        while (reader.read())
        {
            // Get the value of the result set
            var result =  reader.getValue(1, ncache.JsonDataType.Object);
            var category =  reader.getValue(0, Number());
        }
    } 
    else
    {
        // Null query result set retrieved
    }

}
catch (error)
{
    // Handle errors
}

Additional Resources