Tablestore:Collapse (distinct)

Prerequisites

• The OTSClient is initialized. For more information, see Initialize an OTSClient instance.

• A data table is created. Data is written to the table.

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

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 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.

Parameters

Example

The following sample code provides an example on how to query the rows in which the value of the user_id column matches "00002" and then collapse the result set based on the value of the product_name column:

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. 
}

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?

• Why does a token become invalid when pagination is used in a search index-based query?

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, geo query, Boolean query, KNN vector query, nested query, and exists query. You can use the query methods provided by the search index to query data from multiple dimensions based on your business requirements.

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