Tidb: Call For Participation: finish the unsupported aggregate functions

[zz-jason]

All issues are open and welcomed to contributors. You can join #sig-exec on tidb community slack to discuss and get help from someone.

Description

At present, the aggregate functions that TiDB supports are:

• AVG()
• BIT_AND()
• BIT_OR()
• BIT_XOR()
• COUNT()
• COUNT(DISTINCT)
• GROUP_CONCAT()
• MAX()
• MIN()
• SUM()

In order to be compatible with MySQL and Improve the usability of TiDB, the following functions should also be supported in TiDB:

| Name | Description |
|--------------------|-------------------------------------------|
| STD() | Alias for STDDEV_POP function |
| STDDEV() | Alias for STDDEV_POP function |
| STDDEV_POP() | Return the population standard deviation |
| STDDEV_SAMP() | Return the sample standard deviation |
| VARIANCE() | Return the population standard variance |
| VAR_POP() | Return the population standard variance |
| VAR_SAMP() | Return the sample variance |
| JSON_ARRAYAGG() | Return result set as a single JSON array |
| JSON_OBJECTAGG() | Return result set as a single JSON object |

An implementation checklist:

• [x] STD()/STDDEV()/STDDEV_POP() @Win-Man #19195
• [x] STDDEV_SAMP() @Win-Man #19810
• [x] VARIANCE()/VAR_POP() @githubFZX #14101
• [x] VAR_SAMP() @Win-Man #19810
• [ ] JSON_ARRAYAGG() https://github.com/pingcap/tidb/pull/19957
• [x] JSON_OBJECTAGG() @hg2990656 #11154

Difficulty

• Medium

Score

• 3000

Mentor(s)

• @qw4990

Recommended Skills

• SQL Optimization
• Golang Profiling
• Code Refactoring

[Win-Man]

Pick up

• [x] STD()/STDDEV()/STDDEV_POP() PR: https://github.com/pingcap/tidb/pull/19195
• [x] STDDEV_SAMP()
• [x] VAR_SAMP()

[ti-challenge-bot[bot]]

Pick up success.

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This issue already picked by Blue-Sail.

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This issue already picked by Blue-Sail.

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Give up success.

[arthuryangcs]

/pick-up JSON_ARRAYAGG

[ti-challenge-bot[bot]]

Pick up success.

[ti-challenge-bot[bot]]

@arthuryangcs You did not submit PR within 7 days, so give up automatically.

[arthuryangcs]

/pick-up JSON_ARRAYAGG

[ti-challenge-bot[bot]]

Pick up success.

[ti-challenge-bot[bot]]

@arthuryangcs You did not submit PR within 7 days, so give up automatically.

[arthuryangcs]

/pick-up JSON_ARRAYAGG

[ti-challenge-bot[bot]]

Pick up success.

[ti-challenge-bot[bot]]

@arthuryangcs You did not submit PR within 7 days, so give up automatically.