SQL supports hidden columns: columns that are only included in a projection if explicitly requested. An example of this is the rowid column that is created on tables without explicitly primary keys.

Currently, there is no way to get a hidden column on a user-defined table: it's only possible if you manually set the hidden boolean in the table descriptor, by editing the CockroachDB source code.

It could conceivably be useful for users to define hidden columns on their own tables. This issue tracks adding that functionality. It should be pretty straightforward, and reasonably suitable for a new contributor.

• Add an HIDDEN keyword to pkg/sql/parser/sql.y as an optional modifier to columns for creation and modification. e.g. CREATE TABLE a (a INT HIDDEN), ALTER TABLE a ALTER COLUMN a [SET|DROP] HIDDEN
• Add a HIDDEN attribute to ColumnTableDef in pkg/sql/sem/tree/create.go
• Update MakeColumnDefDescs in pkg/sql/catalog/tabledesc/table.go to set Hidden on the column descriptor if the attribute above is set
• Add AlterTableSetHidden AST nodes to pkg/sql/sem/tree/alter_table.go
• Add cases for those AST nodes in pkg/sql/alter_table.go
• Add logic tests that verify that hidden columns work as expected. A good place for these would be in pkg/sql/logictest/testdata/logic_test/hidden.