You can use the collapse (distinct) feature to collapse the result set based on a specified column when the results of a query contain large amounts of data of a specific type. Data of the specific type is displayed only once in the query results to ensure diversity of the result types.

In most scenarios, you can use the collapse (distinct) feature to obtain distinct values based on the columns that are collapsed. However, this feature is supported only for columns whose values are of the INTEGER, FLOATING-POINT or KEYWORD type. Only the first 10,000 sorted results are returned.

Usage notes

  • If you use the collapse (distinct) feature, you can perform pagination only by specifying offset and limit instead of token.
  • 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 query results, the total number of results that are returned is determined by the sum of the offset and limit values. A maximum of 10,000 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 operations

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

Use Tablestore SDKs

You can use the following Tablestore SDKs to perform the collapse (distinct) feature:

Parameters

Parameter Description
query The query type. You can set this parameter to any query type.
collapse The collapse parameter, including the fieldName field.

fieldName: the name of the column based on which the result set is collapsed. Only columns whose values are of the INTEGER, FLOATING-POINT, or KEYWORD type are supported.

offset The position from which the current query starts.
limit The maximum number of rows that you want the current query to return.

To query only the number of rows that meet the query conditions without returning specific data, you can set limit to 0. This way, Tablestore returns the number of rows that meet the query conditions without specific data from the table.

getTotalCount Specifies whether to return the total number of rows that meet the query conditions. The default value of this parameter is false, which indicates that the total number of rows that meet the query conditions is not returned.

If you set this parameter to true, the query performance is compromised.

tableName The name of the data table.
indexName The name of the search index.
columnsToGet Specifies whether to return all columns of each row that meets the query conditions. You can configure returnAll and columns for this parameter.

The default value of returnAll is false, which indicates that not all columns are returned. In this case, you can use columns to specify the columns that you want to return. If you do not specify the columns that you want to return, only the primary key columns are returned.

If you set returnAll to true, all columns are returned.

Examples

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);
    searchQuery.setLimit(20);
    //searchQuery.setGetTotalCount(true);// Set GetTotalCount to true to return the total number of rows that meet the query conditions. 

    SearchRequest searchRequest = new SearchRequest("sampleTable", "sampleSearchIndex", searchQuery);// Specify the names of the data table and the search index.     // You can configure the columnsToGet parameter to specify the columns to return or specify that all columns are returned. If you do not configure this parameter, only the primary key columns are returned. 
    //SearchRequest.ColumnsToGet columnsToGet = new SearchRequest.ColumnsToGet();
    //columnsToGet.setReturnAll(true); // Set ReturnAll 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. 
}