Implement SHOW FUNCTIONS

[goldmedal]

Which issue does this PR close?

Closes #12144.

Rationale for this change

This PR implements SHOW FUNCTIONS to list the available functions during runtime. Instead of listing the function name only (like Apache Spark), I think it's better to provide more information like what Snowflake did.

To provide the required information, I also added some columns to information_schema.routines and information_schema.parameters.

Syntax

SHOW FUNCTIONS [ LIKE <pattern> ];

Sample Output

> show functions like '%datetrunc';
+---------------+-------------------------------------+-------------------------+-------------------------------------------------+---------------+-------------------------------------------------------+-----------------------------------+
| function_name | return_type                         | parameters              | parameter_types                                 | function_type | description                                           | syntax_example                    |
+---------------+-------------------------------------+-------------------------+-------------------------------------------------+---------------+-------------------------------------------------------+-----------------------------------+
| datetrunc     | Timestamp(Microsecond, Some("+TZ")) | [precision, expression] | [Utf8, Timestamp(Microsecond, Some("+TZ"))]     | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Nanosecond, None)         | [precision, expression] | [Utf8View, Timestamp(Nanosecond, None)]         | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Second, Some("+TZ"))      | [precision, expression] | [Utf8View, Timestamp(Second, Some("+TZ"))]      | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Microsecond, None)        | [precision, expression] | [Utf8View, Timestamp(Microsecond, None)]        | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Second, None)             | [precision, expression] | [Utf8View, Timestamp(Second, None)]             | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Microsecond, None)        | [precision, expression] | [Utf8, Timestamp(Microsecond, None)]            | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Second, None)             | [precision, expression] | [Utf8, Timestamp(Second, None)]                 | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Microsecond, Some("+TZ")) | [precision, expression] | [Utf8View, Timestamp(Microsecond, Some("+TZ"))] | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Nanosecond, Some("+TZ"))  | [precision, expression] | [Utf8, Timestamp(Nanosecond, Some("+TZ"))]      | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Millisecond, None)        | [precision, expression] | [Utf8, Timestamp(Millisecond, None)]            | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Millisecond, Some("+TZ")) | [precision, expression] | [Utf8, Timestamp(Millisecond, Some("+TZ"))]     | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Second, Some("+TZ"))      | [precision, expression] | [Utf8, Timestamp(Second, Some("+TZ"))]          | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Nanosecond, None)         | [precision, expression] | [Utf8, Timestamp(Nanosecond, None)]             | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Millisecond, None)        | [precision, expression] | [Utf8View, Timestamp(Millisecond, None)]        | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Millisecond, Some("+TZ")) | [precision, expression] | [Utf8View, Timestamp(Millisecond, Some("+TZ"))] | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
| datetrunc     | Timestamp(Nanosecond, Some("+TZ"))  | [precision, expression] | [Utf8View, Timestamp(Nanosecond, Some("+TZ"))]  | SCALAR        | Truncates a timestamp value to a specified precision. | date_trunc(precision, expression) |
+---------------+-------------------------------------+-------------------------+-------------------------------------------------+---------------+-------------------------------------------------------+-----------------------------------+
16 row(s) fetched. 

The Output Schema

• function_name
• return_type
• parameters: The name of parameters (ordered by the ordinal position)
• parameter_types: The type of parameters (ordered by the ordinal position)
• description: The description of the function (the description defined in the document)
• syntax_example: The syntax_example of the function (the syntax_example defined in the document)

What changes are included in this PR?

• Implement SHOW FUNCTIONS.
• Add the syntax_example field to information_schema.routines.
• Add the rid field to information_schema.parameters.
  • rid (short for routine id) is used to differentiate parameters from different signatures (it serves as the group-by key when generating the SHOW FUNCTIONS query). For example, the following signatures have different rid values:
    • datetrunc(Utf8, Timestamp(Microsecond, Some("+TZ"))) -> Timestamp(Microsecond, Some("+TZ"))
    • datetrunc(Utf8View, Timestamp(Nanosecond, None)) -> Timestamp(Nanosecond, None)

Are these changes tested?

yes, tested by sqllogictests

Are there any user-facing changes?

New SQL syntax.