Describe error handling best practice in Code Style and Quality Guide

[tisonkun]

The best practices of reporting errors:

1. The error message should be more user-friendly. Bad case: The table 101 exceeds table size. Good case: The table tbl exceeds table size.
2. Provide workarounds if necessary. Bad case: The table tbl exceeds table size. Good case: The table tbl exceeds table size. Please try to turn up the value of the system variable tmp_table_size.
3. Define an error code when it's a general error. Bad case: The table tbl exceeds table size. Good case: Error 1001: The table tbl exceeds table size.
4. Report the error as early as possible. If you can judge it in the preprocess phase, don't report it in the planner phase. If you can judge it in the planner phase, don't report it in the executor phase. The premise is not breaking the readability and simplicity of the code.

Originally posted by @djshow832 in #26 (comment)