If the query processor runs into any error, it terminates the ongoing query processing and immediately returns an error message to the client.
A SQL++ query can potentially result in one of the following types of errors:
A valid SQL++ query must satisfy the SQL++ grammar rules. Otherwise, a syntax error is displayed.
SELECT * FROM GleambookUsers user
Since the ending semi-colon (;) is mandatory for any SQL++ query, the following syntax error is displayed:
Error: Syntax error: In line 2 >>FROM GleambookUsers user<< Encountered <EOF> at column 24. ==> FROM GleambookUsers user
SELECT * FROM GleambookUsers user WHERE type="advertiser";
Since type is a reserved keyword in the SQL++ parser, the following syntax error is displayed:
Error: Syntax error: In line 3 >>WHERE type="advertiser";<< Encountered 'type' "type" at column 7. ==> WHERE type="advertiser";
Referring an undefined identifier can cause an error if the identifier cannot be successfully resolved as a valid field access.
SELECT * FROM GleambookUser user;
Let’s assume you have a spelling mistake in the GleambookUser and you missed the ending s, then the following identifier resolution error is displayed:
Error: Cannot find dataset GleambookUser in dataverse Default nor an alias with name GleambookUser!
SELECT name, message FROM GleambookUsers u JOIN GleambookMessages m ON m.authorId = u.id;
If the compiler cannot figure out all possible fields in
GleambookMessages, then an identifier resolution error is displayed:
Error: Cannot resolve ambiguous alias reference for undefined identifier name
The SQL++ compiler does type checks based on its available type information. In addition, the SQL++ runtime also reports type errors if a data model instance it processes does not satisfy the type requirement.
abs can only process numeric input values, the following type error is displayed:
Error: Arithmetic operations are not implemented for string
A query can potentially exhaust system resources, such as the number of open files and disk spaces. For instance, the following two resource errors can be potentially seen when running the system:
Error: no space left on device Error: too many open files
The no space left on device issue can be fixed by cleaning up the disk space and reserving more disk space for the system. The too many open files issue can be fixed by a system administrator using these instructions.