Goal

1. CREATE TABLE with duplicate column name should get Error

gluesql> CREATE TABLE Item (id INT, id INT);
[error] duplicate column name: id

2. RENAME COLUMN with duplicated column name should get Error

gluesql> CREATE TABLE Item (id INT, name TEXT);
Table created

gluesql> ALTER TABLE Item RENAME COLUMN name to id;
[error] column already exists: id

3. ADD COLUMN already has validation.

Todo

• implement validate_column_names
• add validation to rename_column at sled-storage, memory-storage
• rename AddColumnAlreadyExists to ColumnAlreadyExists