expression - mysql

实现 generate_series 函数

按照参数输出序列
- null in null out，有任何参数为null，则输出null
- 2 个参数，则从 start 到 end 输出，数值类型步长为1，时间类型不接受两个参数，必须指定步长，那个参数在前面，就使用那个参数的类型
- 3 个参数，则从 start 到 end 输出，步长为 step，时间类型步长为 step，输出类型为所有参数的公共类型
- step 可以指定为负，此时输出序列为倒序
- test 使用 duckdb 和 pg
- 多次调用时候，函数状态
  - MySQL 有那些函数是有状态的函数
- 参数为表达式
  - 嵌套复杂表达式
  - 子查询
- 返回的是 record ，类似表的形式
  - 函数一般返回一行，或者一个值
    - pg 使用的是 Function Scan 调用，
  - MySQL 对应的是什么
    - MySQL 怎么把函数作为一个表
- MySQL 不允许 select * from fun(), 只能 select func，func 不能出现在表的位置
  - 能出现在表的位置的
- 社区可能不是不想做，而是前置要求多

# non-persistent series generator
{ oid => '1066',  proname => 'generate_series', prorows => '1000', prosupport => 'generate_series_int4_support', proretset => 't', prorettype => 'int4', proargtypes => 'int4 int4 int4', prosrc => 'generate_series_step_int4' },
{ oid => '1067',  proname => 'generate_series', prorows => '1000', prosupport => 'generate_series_int4_support', proretset => 't', prorettype => 'int4', proargtypes => 'int4 int4', prosrc => 'generate_series_int4' },
{ oid => '3994',  proname => 'generate_series_int4_support', prorettype => 'internal', proargtypes => 'internal', prosrc => 'generate_series_int4_support' },
{ oid => '1068',  proname => 'generate_series', prorows => '1000', prosupport => 'generate_series_int8_support', proretset => 't', prorettype => 'int8', proargtypes => 'int8 int8 int8', prosrc => 'generate_series_step_int8' },
{ oid => '1069',  proname => 'generate_series', prorows => '1000', prosupport => 'generate_series_int8_support', proretset => 't', prorettype => 'int8', proargtypes => 'int8 int8', prosrc => 'generate_series_int8' },
{ oid => '3995',  proname => 'generate_series_int8_support', prorettype => 'internal', proargtypes => 'internal', prosrc => 'generate_series_int8_support' },
{ oid => '3259',  proname => 'generate_series', prorows => '1000', proretset => 't', prorettype => 'numeric', proargtypes => 'numeric numeric numeric', prosrc => 'generate_series_step_numeric' },
{ oid => '3260',  proname => 'generate_series', prorows => '1000', proretset => 't', prorettype => 'numeric', proargtypes => 'numeric numeric', prosrc => 'generate_series_numeric' },
{ oid => '938',  proname => 'generate_series', prorows => '1000', proretset => 't', prorettype => 'timestamp', proargtypes => 'timestamp timestamp interval', prosrc => 'generate_series_timestamp' },
{ oid => '939',  proname => 'generate_series', prorows => '1000', proretset => 't', provolatile => 's', prorettype => 'timestamptz', proargtypes => 'timestamptz timestamptz interval', prosrc => 'generate_series_timestamptz' },
{ oid => '6274',  proname => 'generate_series', prorows => '1000', proretset => 't', prorettype => 'timestamptz', proargtypes => 'timestamptz timestamptz interval text', prosrc => 'generate_series_timestamptz_at_zone' },

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实现 generate_series 函数