Improve the federated query MySQL function

[zihaoAK47]

Background

Hi Community,

Federated queries help users perform cross-database join queries, subqueries, and aggregate queries. Currently, we plan to enhance MySQL functions in the federated query environment to support more SQL execution scenarios in federated query contexts.

For more details, please refer to: Apache ShardingSphere Documentation on SQL Federation.

Task

• [x] ATAN link @zihaoAK47
• [ ] BENCHMARK link
• [ ] BIN link @zihaoAK47
• [ ] CRC32 link
• [ ] SUBSTRING_INDEX link
• [ ] FORMAT link
• [ ] CONV link
• [ ] SUBSTRING link
• [ ] CHAR link
• [ ] ELT link
• [ ] EXPORT_SET link
• [ ] FIELD link
• [ ] FIND_IN_SET link
• [ ] HEX link
• [ ] INSERT link
• [ ] LCASE link
• [ ] LOAD_FILE link
• [ ] LPAD link
• [ ] LTRIM link
• [ ] MAKE_SET link
• [ ] MID link
• [ ] OCT link
• [ ] OCTET_LENGTH link
• [ ] ORD link
• [ ] QUOTE link
• [ ] REGEXP_INSTR link
• [ ] REGEXP_LIKE link
• [ ] REGEXP_SUBSTR link
• [ ] RPAD link
• [ ] AES_ENCRYPT link
• [ ] AES_DECRYPT link
• [ ] RTRIM link
• [ ] UNHEX link
• [ ] UCASE link
• [ ] WEIGHT_STRING link
• [ ] CHARSET link
• [ ] COERCIBILITY link
• [ ] FROM_UNIXTIME link
• [ ] CEILING link
• [ ] LOG link
• [ ] LOG2 link
• [ ] POW link
• [ ] TIMEDIFF link
• [ ] LEAST link
• [ ] SHA link

TODO other function

[strongduanmu]

This is an exciting task that will greatly improve the compatibility of federation queries.