SQL Server

Informational schema

SELECT * FROM sys.tables;
SELECT * FROM sys.views;
SELECT * FROM sys.indexes;
SELECT * FROM sys.types;

SELECT * FROM information_schema.tables;

Table stats

Individual table:

EXEC sp_spaceused NAME;

All tables in a schema:

sp_msforeachtable 'EXEC sp_spaceused [?]';

List collations

SELECT name, description FROM sys.fn_helpcollations();

Finding expression type

SELECT SQL_VARIANT_PROPERTY(current_timestamp, 'BaseType');
SELECT SQL_VARIANT_PROPERTY(current_timestamp, 'Precision');
SELECT SQL_VARIANT_PROPERTY(current_timestamp, 'Scale');
SELECT SQL_VARIANT_PROPERTY(current_timestamp, 'MaxLength');

Number of bytes required to hold both the metadata and data of the value:

SELECT SQL_VARIANT_PROPERTY(current_timestamp, 'TotalBytes');

https://learn.microsoft.com/en-us/sql/t-sql/functions/sql-variant-property-transact-sql

SQL_VARIANT_PROPERTY (Transact-SQL).