Tablestore:Collapse (distinct)

Usage notes

• If you use the collapse (distinct) feature, you can perform pagination only by specifying the offset and limit parameters.

• If you aggregate and collapse a result set at the same time, the result set is aggregated before it is collapsed.

• If you collapse the results of a query, the total number of results that are returned is determined by the sum of the values of the offset and limit parameters. A maximum of 50,000 results can be returned.

• The total number of rows in the response indicates the number of rows that meet the query conditions before you use the collapse (distinct) feature. After the result set is collapsed, the total number of distinct values cannot be queried.

API operation

You can configure the collapse parameter in the Search operation to implement the collapse (distinct) feature.

Parameters

Methods

You can collapse the results of a data query by using the Tablestore CLI or Tablestore SDKs. Before you use the collapse (distinct) feature, make sure that the following prerequisites are met:

• You have an Alibaba Cloud account or a RAM user that has permissions to perform operations on Tablestore. For information about how to grant Tablestore operation permissions to a RAM user, see Use a RAM policy to grant permissions to a RAM user.

  If you want to use Tablestore SDKs or the Tablestore CLI to perform a query, an AccessKey pair is created for your Alibaba Cloud account or RAM user. For more information, see Create an AccessKey pair.

• A data table is created. For more information, see Operations on tables.

• A search index is created for the data table. For more information, see Create a search index.

• If you want to use Tablestore SDKs to perform a query, an OTSClient instance is initialized. For more information, see Initialize an OTSClient instance.

• If you want to use the Tablestore CLI to perform a query, the Tablestore CLI is downloaded and started, and information about the instance that you want to access and the data table are configured. For more information, see Download the Tablestore CLI, Start the Tablestore CLI and configure access information, and Operations on data tables.

private static void UseCollapse(SyncClient client){
    SearchQuery searchQuery = new SearchQuery(); // Specify the query conditions. 
    MatchQuery matchQuery = new MatchQuery();
    matchQuery.setFieldName("user_id");
    matchQuery.setText("00002");

    searchQuery.setQuery(matchQuery);
    Collapse collapse = new Collapse("product_name"); // Collapse the result set based on the product_name column. 
    searchQuery.setCollapse(collapse);

    //searchQuery.setOffset(1000);// The position from which the current query starts. 
    searchQuery.setLimit(20);
    //searchQuery.setGetTotalCount(true);// Set the GetTotalCount parameter to true to return the total number of rows that meet the query conditions. 

    SearchRequest searchRequest = new SearchRequest("<TABLE_NAME>", "<SEARCH_INDEX_NAME>", searchQuery);// Specify the name of the data table and the name of the search index.     
    // You can use the columnsToGet parameter to specify the columns that you want to return or specify that all columns are returned. If you do not specify this parameter, only the primary key columns are returned. 
    //SearchRequest.ColumnsToGet columnsToGet = new SearchRequest.ColumnsToGet();
    //columnsToGet.setReturnAll(true); // Set the ReturnAll parameter to true to return all columns. 
    //columnsToGet.setColumns(Arrays.asList("ColName1","ColName2")); // Specify the columns that you want to return. 
    //searchRequest.setColumnsToGet(columnsToGet);

    SearchResponse response = client.search(searchRequest);  
    //System.out.println(response.getTotalCount());    
    //System.out.println(response.getRows().size()); // Display the number of rows that are returned based on the product_name column. 
    System.out.println(response.getRows()); // Display the product names that are returned based on the product_name column. 
}

Billing rules

If you use search indexes to query data, read throughput is consumed. For more information, see Billable items of search indexes.

The collapse (distinct) feature does not affect the existing billing rules.

FAQ

• What do I do if no data can be found by calling the Search operation?

• How do I increase the value of the limit parameter to 1000 when I call the Search operation of the search index feature to query data?

References

• When you use a search index to query data, you can use the following query methods: term query, terms query, match all query, match query, match phrase query, prefix query, range query, wildcard query, fuzzy query, Boolean query, geo query, nested query, KNN vector query, and exists query. You can select query methods based on your business requirements to query data from multiple dimensions.

  You can sort or paginate rows that meet the query conditions by using the sorting and paging features. For more information, see Perform sorting and paging.

  You can use the collapse (distinct) feature to collapse the result set based on a specific column. This way, data of the specified type appears only once in the query results. For more information, see Collapse (distinct).

• If you want to analyze data in a data table, you can use the aggregation feature of the Search operation or execute SQL statements. For example, you can obtain the minimum and maximum values, sum, and total number of rows. For more information, see Aggregation and SQL query.

• If you want to obtain all rows that meet the query conditions without the need to sort the rows, you can call the ParallelScan and ComputeSplits operations to use the parallel scan feature. For more information, see Parallel scan.