The key keyword definition section of `sql_parser.cup` is unordered and messy:
1. It is almost unreadable
2. There are no rules to format it when we make a change to it
3. **It takes unnecessary effort to resolve conflict caused by the unordered keywords**
We can apply some simple rules to format it:
1. Sort in lexicographical order
4. Break into several "sections", keywords in each section have the same prefix `KW_${first_letter}`
5. Every 2 sections are connected with an empty line containing only 4 white spaces
e.g.
```
terminal String
KW_A...
KW_B...
...
KW_Z...
```
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