builtin: add make_set built-in function

[ariesdevil]

No description provided.

[CLAassistant]

All committers have signed the CLA.

[shenli]

if args[0].IsNull(), mysql will return null.
mysql> SELECT MAKE_SET(NULL,'a','b','c');
+----------------------------+
| MAKE_SET(NULL,'a','b','c') |
+----------------------------+
| NULL |
+----------------------------+

[shenli]

It is better to use int bit-wise and shift operation. Not string compare.

[ariesdevil]

@shenli fixed and plz review again.

[coocood]

LGTM
Thank you for your PR!

[coocood]

Sorry for the delay, there are many PRs conflicting on typeinfer files.
Merging each one makes other PRs conflicting, so we have to queue the PRs.
when this PR is ready to merge, we will notify you to resolve conflicts.

[ariesdevil]

OK, got it.

[tiancaiamao]

The test could not reflect the reality, if you run the binary, you'll get this:

mysql> SELECT MAKE_SET(-100 | 4,'a','b','c');
ERROR 1105 (HY000): constant 18446744073709551516 overflows bigint

That's because, -100 | 4 will be calculate directly in test code, while it should be done in TiDB as an expression.

{[]interface{}{-100 | 4, "hello", "nice", "abc", "world"}, "abc,world"},

Okay, it involves another problem.

LGTM

[ariesdevil]

@tiancaiamao I test on my machine and it works well (mysql version: 5.7.17):

mysql> SELECT MAKE_SET(-100 | 4,'a','b','c');
+--------------------------------+
| MAKE_SET(-100 | 4,'a','b','c') |
+--------------------------------+
| c                              |
+--------------------------------+
1 row in set (0.00 sec)