HTSQL errors are reported as HTTP responses with corresponding status code in the header following HTTP protocol specification. Status codes and their meaning in HTSQL is shown in the table below.
| HTTP status code | Error reason | Description |
|---|---|---|
| 400 Bad Request | The request contains bad syntax. | |
| invalid syntax | Invalid syntax of the HTSQL query. | |
| invalid query | The HTSQL query is found inappropriate. Is raised when illegal command call is encountered. | |
| invalid reference | An identifier refers to an unsuitable entity. | |
| invalid argument | Invalid semantics of the HTSQL query. | |
| unknown class id | An identifier does not refer to a known class. | |
| ambiguous class id | An identifier refers to more than one class. | |
| incompatible class | An identifier refers to a class incompatible with the arguments. | |
| unknown object id | An identifier does not refer to a known object. | |
| ambiguous object id | An identifier refers to more than one object. | |
| 403 Forbidden | The request is denied for security reasons | |
| 404 Not Found | Resource not found. | |
| 409 Conflict | The state of the resource prevents the request from being completed. | |
| failed expectation | Unexpected number of rows affected by query processor command. | |
| 500 Internal Server Error | Implementation error. | |
| 501 Not Implemented | A feature is not implemented. |