[feature](nereids): SimplifyCastRule

[jackwener]

Proposed changes

Issue Number: close #xxx

Problem summary

• Remove redundant cast like
  • cast(1 as int) -> 1.
• Merge cast like
  • cast(cast(1 as bigint) as string) -> cast(1 as string).

Checklist(Required)

1. Does it affect the original behavior:
   • [x] Yes
   • [ ] No
   • [ ] I don't know
2. Has unit tests been added:
   • [x] Yes
   • [ ] No
   • [ ] No Need
3. Has document been added or modified:
   • [ ] Yes
   • [ ] No
   • [x] No Need
4. Does it need to update dependencies:
   • [ ] Yes
   • [x] No
5. Are there any changes that cannot be rolled back:
   • [ ] Yes (If Yes, please explain WHY)
   • [x] No

Further comments

If this is a relatively large or complex change, kick off the discussion at [email protected] by explaining why you chose the solution you did and what alternatives you considered, etc...

[englefly]

The following two casts are not equivalent.

mysql> select cast(cast("1990-09-01 1:00:00" as datetime) as int); +-----------------------------------------------------+ | CAST(CAST('1990-09-01 1:00:00' AS DATETIME) AS INT) | +-----------------------------------------------------+ | -1977439664 | +-----------------------------------------------------+ 1 row in set (0.01 sec)

mysql> select cast("1990-09-01 1:00:00" as int); +-----------------------------------+ | CAST('1990-09-01 1:00:00' AS INT) | +-----------------------------------+ | NULL | +-----------------------------------+ 1 row in set (0.01 sec)

[github-actions[bot]]

PR approved by at least one committer and no changes requested.

[github-actions[bot]]

PR approved by anyone and no changes requested.