Java

Data Query Process

使用下方的示例代码来查询数据：

java

  1. QueryRequest request = QueryRequest.newBuilder()
  2.     .exprType(SelectExprType.Sql) // Currently, only SQL is supported, and more query methods will be supported in the future
  3.     .ql("SELECT * FROM monitor;")
  4.     .build();
  6. // For performance reasons, the SDK is designed to be purely asynchronous.
  7. // The return value is a future object. If you want to immediately obtain
  8. // the result, you can call `future.get()`.
  9. CompletableFuture<Result<QueryOk, Err>> future = greptimeDB.query(request);
  10. Result<QueryOk, Err> result = future.get();
  12. if (result.isOk()) {
  13.     QueryOk queryOk = result.getOk();
  14.     SelectRows rows = queryOk.getRows();
  15.     // `collectToMaps` will discard type information, if type information is needed,
  16.     // please use `collect`.
  17.     List<Map<String, Object>> maps = rows.collectToMaps();
  18.     for (Map<String, Object> map : maps) {
  19.         LOG.info("Query row: {}", map);
  20.     }
  21. } else {
  22.     LOG.error("Failed to query: {}", result.getErr());
  23. }

The code will output the details of querying which will look something like this:

  1. [main] INFO  QuickStart:114 - Query row: {memory=null, host=127.0.0.1, cpu=0.1, ts=2023-03-16T07:20:26.043}
  2. [main] INFO  QuickStart:114 - Query row: {memory=null, host=127.0.0.1, cpu=0.1, ts=2023-03-16T07:21:48.050}
  3. [main] INFO  QuickStart:114 - Query row: {memory=null, host=127.0.0.1, cpu=0.1, ts=2023-03-16T07:29:47.780}
  4. [main] INFO  QuickStart:114 - Query row: {memory=0.5, host=127.0.0.2, cpu=0.3, ts=2023-03-16T07:20:26.096}
  5. [main] INFO  QuickStart:114 - Query row: {memory=0.5, host=127.0.0.2, cpu=0.3, ts=2023-03-16T07:21:48.103}
  6. [main] INFO  QuickStart:114 - Query row: {memory=0.5, host=127.0.0.2, cpu=0.3, ts=2023-03-16T07:29:47.882}

查询 API

java

  1. /**
  2.  * According to the conditions, query data from the DB.
  3.  *
  4.  * @param req the query request
  5.  * @param ctx invoke context
  6.  * @return query result
  7.  */
  8. CompletableFuture<Result<QueryOk, Err>> query(QueryRequest req, Context ctx);