Adds information_schema.views

[killme2008]

What type of enhancement is this?

API improvement, Configuration, User experience

What does the enhancement do?

Part of #2931 #3729

Implements information_schema.views to provide information about views in databases.

Refer to https://dev.mysql.com/doc/refman/8.4/en/information-schema-views-table.html

Implementation challenges

The implement detail notes:

1. Refer to information_schema.tables for example to implement the views:
   • https://github.com/GreptimeTeam/greptimedb/blob/main/src/catalog/src/information_schema/tables.rs
2. Register it to information_schema:

   • greptimedb/src/catalog/src/information_schema.rs

     Line 211 in da0c840

     TABLES => Some(Arc::new(InformationSchemaTables::new(

3. Adds unit tests and sqlness tests https://github.com/GreptimeTeam/greptimedb/tree/main/tests/cases/standalone/common/information_schema

[lyang24]

Hi, I would like to work on this. Do we store the view definition statements somewhere? i checked ViewInfoManager it stores the raw plan logical info as bytes we probably don't want to display that to users?

This is what i found on mysql example link
+----------------------------------+
| VIEW_DEFINITION |
+----------------------------------+
| select concat('a','b') AS col1 |
+----------------------------------+

[killme2008]

@lyang24 Great, thanks a lot.

There is a field definition which is the view definition:

greptimedb/src/common/meta/src/key/view_info.rs

Line 94 in da0c840

pub definition: String,

Retrieving the view_info by ViewInfoCache:

greptimedb/src/common/meta/src/cache/table/view_info.rs

Line 30 in da0c840

pub type ViewInfoCache = CacheContainer<TableId, Arc<ViewInfoValue>, CacheIdent>;

ViewInfoCache can be retrieved by:

greptimedb/src/catalog/src/kvbackend/manager.rs

Line 103 in da0c840

pub fn view_info_cache(&self) -> Result<ViewInfoCacheRef> {

[killme2008]

One way to obtain the ViewInfoCache is by incorporating a function similar to the following:

greptimedb/src/catalog/src/information_schema/utils.rs

Line 57 in da0c840

pub fn table_meta_manager(

During runtime, the catalog_manager is consistently KvBackendCatalogManager.

[killme2008]

Another example to retrieve view info in catalog crate:

greptimedb/src/catalog/src/table_source.rs

Lines 135 to 143 in da0c840

	let view_info = catalog_manager
	.view_info_cache()?
	.get(table.table_info().ident.table_id)
	.await
	.context(GetViewCacheSnafu)?
	.context(ViewInfoNotFoundSnafu {
	name: &table.table_info().name,
	})?;