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Errors

A SQL++ query can potentially result in one of the following errors:

  • syntax error,

  • identifier resolution error,

  • type error,

  • resource error.

If the query processor runs into any error, it will terminate the ongoing processing of the query and immediately return an error message to the client.

Syntax Errors

An valid SQL++ query must satisfy the SQL++ grammar rules. Otherwise, a syntax error will be raised.

Example
SELECT *
GleambookUsers user

Since the query misses a FROM keyword before the dataset GleambookUsers, we will get a syntax error as follows:

Syntax error: In line 2 >>GleambookUsers user;<< Encountered <IDENTIFIER> \"GleambookUsers\" at column 1.
Example
SELECT *
FROM GleambookUsers user
WHERE type="advertiser";

Since "type" is a reserved keyword in the SQL++ parser, we will get a syntax error as follows:

Error: Syntax error: In line 3 >>WHERE type="advertiser";<< Encountered 'type' "type" at column 7.
==> WHERE type="advertiser";

Identifier Resolution Errors

Referring to an undefined identifier can cause an error if the identifier cannot be successfully resolved as a valid field access.

Example
SELECT *
FROM GleambookUser user;

If we have a typo as above in "GleambookUsers" that misses the dataset name’s ending "s", we will get an identifier resolution error as follows:

Error: Cannot find dataset GleambookUser in dataverse Default nor an alias with name GleambookUser!
Example
SELECT name, message
FROM GleambookUsers u JOIN GleambookMessages m ON m.authorId = u.id;

If the compiler cannot figure out how to resolve an unqualified field name, which will occur if there is more than one variable in scope (e.g., GleambookUsers u and GleambookMessages m as above), we will get an identifier resolution error as follows:

Error: Cannot resolve ambiguous alias reference for undefined identifier name

Type Errors

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.

Example
abs("123");

Since function abs can only process numeric input values, we will get a type error as follows:

Error: Type mismatch: function abs expects its 1st input parameter to be type tinyint, smallint, integer, bigint, float or double, but the actual input type is string

Resource Errors

A query can potentially exhaust system resources, such as the number of open files and disk spaces. For instance, the following two resource errors could be potentially be seen when running the system:

Error: no space left on device
Error: too many open files

The "no space left on device" issue usually can be fixed by cleaning up disk spaces and reserving more disk spaces for the system. The "too many open files" issue usually can be fixed by a system administrator, following the instructions here.