You can perform a prefix query to query data that matches the specified prefix. If the field used to match the prefix condition is a TEXT field, the field values are tokenized. A row meets the query conditions when at least one token contains the specified prefix.
Prerequisites
An OTSClient 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 |
query | The type of the query. Set the query parameter to PrefixQuery. |
fieldName | The name of the column that you want to query. |
prefix | The prefix. If the column used to match the prefix condition is a TEXT column, the column is tokenized. A row meets the query conditions when at least one token contains the specified prefix. |
getTotalCount | Specifies whether to return the total number of rows that meet the query conditions. Default value: false. If you set this parameter to true, the query performance is compromised. |
weight | The weight that you want to assign to the column that you want to query to calculate the BM25-based keyword relevance score. This parameter is used in full-text search scenarios. If you specify a higher weight for the column that you want to query, the BM25-based keyword relevance score is higher for the row. The value of this parameter is a positive floating point number. This parameter does not affect the number of rows that are returned. However, this parameter affects the BM25-based keyword relevance scores of the query results. |
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 specify the returnAll and columns fields for this parameter. The default value of the returnAll field is false, which specifies that not all columns are returned. In this case, you can use the columns field 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 the returnAll field to true, all columns are returned. |
Sample code
The following sample code provides an example on how to query the rows in which the value of the Col_Keyword column contains the prefix "hangzhou" in a table:
/**
* Search the table for rows in which the value of Col_Keyword contains the prefix "hangzhou".
* @param client
*/
private static void prefixQuery(SyncClient client) {
SearchQuery searchQuery = new SearchQuery();
PrefixQuery prefixQuery = new PrefixQuery(); // Set the query type to PrefixQuery.
searchQuery.setGetTotalCount(true);
prefixQuery.setFieldName("Col_Keyword");
prefixQuery.setPrefix("hangzhou");
searchQuery.setQuery(prefixQuery);
//searchQuery.setGetTotalCount(true); // Specify that the total number of matched rows is returned.
SearchRequest searchRequest = new SearchRequest("<TABLE_NAME>", "<SEARCH_INDEX_NAME>", searchQuery);
// 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); // Specify that all columns are returned.
//columnsToGet.setColumns(Arrays.asList("ColName1","ColName2")); // Specify the columns that you want to return.
//searchRequest.setColumnsToGet(columnsToGet);
SearchResponse resp = client.search(searchRequest);
//System.out.println("TotalCount: " + resp.getTotalCount()); // Specify that the total number of matched rows instead of the number of returned rows is displayed.
System.out.println("Row: " + resp.getRows());
}
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 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.