Support dummy select without table for string literal

[waynexia]

Description

Support queries like

select "string literal";

Current the execution result is

SELECT 'a';

Failed to execute query, err: Client("Failed to parse schema from JSON")

Proposal

Support this.

Additional context

ref #154

[jiacai2050]

• https://github.com/sqlparser-rs/sqlparser-rs/pull/530

The upstream has already fix this, but not release yet. Just wait a moment 🤔