Perform exists queries by using Tablestore SDK for Python - Tablestore

An exists query is also called a NULL query or NULL-value query. This query is used in sparse data to determine whether a column of a row exists. For example, you can query the rows in which the value of the address column is not empty.

Note

If you want to check whether a column contains empty values, you must use ExistsQuery together with must_not_queries of BoolQuery.
If one of the following conditions is met, the system considers that a column does not exist. In this example, the city column is used.
- The type of the city column in the search index is a basic type such as keyword. If a row in which the city column does not exist in the data table, the search index considers that the city column does not exist.
- The type of the city column in the search index is a basic type such as keyword. If a row in which the value of the city column is an empty array in the data table ("city" = "[]"), the search index considers that the city column does not exist.

Prerequisites

A TableStoreClient instance is initialized. For more information, see Initialize an OTSClient instance.
A data table is created and data is written to the data table. For more information, see Create a data table and Write data.
A search index is created for the data table. For more information, see Create a search index.

Parameters

Parameter	Description
field_name	The name of the column that you want to query.
query	The query type. Set this parameter to ExistsQuery.
get_total_count	Specifies whether to return the total number of rows that meet the query conditions. The default value of this parameter is false, which specifies 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.
table_name	The name of the data table.
index_name	The name of the search index.
columns_to_get	Specifies whether to return all columns of each row that meets the query conditions. You can configure the return_type and column_names fields for this parameter. If you set the return_type field to ColumnReturnType.SPECIFIED, you can use the column_names field to specify the columns to return. If you set the return_type field to ColumnReturnType.ALL, all columns are returned. If you set the return_type field to ColumnReturnType.NONE, only the primary key columns are returned.

Examples

The following examples show how to query the rows in which the value of the city column is not empty.

Perform an exists query by using Tablestore SDK for Python V5.2.1 or later

If you use Tablestore SDK for Python V5.2.1 or later to perform an exists query, a SearchResponse object is returned by default. The following code provides a sample request:

query = ExistsQuery("city")
search_response = client.search(
    '<TABLE_NAME>', '<SEARCH_INDEX_NAME>',
    SearchQuery(query, limit=100, get_total_count=True),
    ColumnsToGet(return_type=ColumnReturnType.ALL)
)
print('request_id : %s' % search_response.request_id)
print('is_all_succeed : %s' % search_response.is_all_succeed)
print('total_count : %s' % search_response.total_count)
print('rows : %s' % search_response.rows)

You can use the following sample request to return results of the Tuple type:

query = ExistsQuery("city")
rows, next_token, total_count, is_all_succeed, agg_results, group_by_results = client.search(
    '<TABLE_NAME>', '<SEARCH_INDEX_NAME>',
    SearchQuery(query, limit=100, get_total_count=True),
    ColumnsToGet(return_type=ColumnReturnType.ALL)
).v1_response()

Perform an exists query by using Tablestore SDK for Python of a version earlier than 5.2.1
If you use a version of Tablestore SDK for Python that is earlier than 5.2.1 to perform an exists query, results of the Tuple type are returned by default. The following code shows a sample request:
```
query = ExistsQuery("city")
rows, next_token, total_count, is_all_succeed = client.search(
    '<TABLE_NAME>', '<SEARCH_INDEX_NAME>',
    SearchQuery(query, limit=100, get_total_count=True),
    ColumnsToGet(return_type=ColumnReturnType.ALL)
)
```

FAQ

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.