pingcap/tidb

Refactor currentTimeFunctionClass and utcTimeFunctionClass

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#27,760 opened on Sep 2, 2021

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help wantedtype/enhancement

Description

Enhancement

currentTimeFunctionClass is very simlier to currentTimeFunctionClass. We can see from the MySQL's code:

class Item_func_curtime_local final : public Item_func_curtime {
 protected:
  Time_zone *time_zone() override;

 public:
  Item_func_curtime_local(const POS &pos, uint8 dec_arg)
      : Item_func_curtime(pos, dec_arg) {}
  const char *func_name() const override { return "curtime"; }
};

class Item_func_curtime_utc final : public Item_func_curtime {
 protected:
  Time_zone *time_zone() override;

 public:
  Item_func_curtime_utc(const POS &pos, uint8 dec_arg)
      : Item_func_curtime(pos, dec_arg) {}
  const char *func_name() const override { return "utc_time"; }
};

This means that we can reuse some codes. After investigation, I found that utcTimeFunctionClass's flen is more accurate than currentTimeFunctionClass. We can fix it by using utcTimeFunctionClass's logic.

Contributor guide

Tech stack
go
Domain
databasebackend
Issue type
refactor
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Understanding of TiDB's expression evaluationBasic knowledge of MySQL time functions
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50
Research direction
The issue points to two similar classes in TiDB: currentTimeFunctionClass and utcTimeFunctionClass. The goal is to refactor them by reusing code, similar to MySQL's approach with Item func curtime local and Item func curtime utc. The fix should align the flen (field length) of currentTimeFunctionClass with the more accurate one from utcTimeFunctionClass. Examine the source files implementing these classes, likely in the 'expression' package (e.g., 'expression/time.go' or similar). Look for any existing comments or linked PRs that discuss this refactoring. The maintainers have not commented on the approach, so implement the refactoring based on the MySQL example provided.