支持很多扩展：
- define: user-defined functions and dynamic sql
- fileio: read and write files
- fuzzy: fuzzy string matching and phonetics
- ipaddr: IP address manipulation
- math: math functions
- regexp: regular expressions
- stats: math statistics
- text: string functions
- unicode: Unicode support
- uuid: Universally Unique IDentifiers
- vsv: CSV files as virtual tables