Describe the solution you'd like
I would like to be able to change the type of a column from SQL, possibly with an expression similar to ALTER COLUMN.

Additional context
Current SQL for adding an index to an existing column:

ALTER TABLE trades ALTER COLUMN instrument ADD INDEX;

implementation

This can be broken down into tasks

• Save column order in table _metadata that is used in SELECT * queries
• Support of SQL syntax and create AlterOperation
• Support of changing the column type as a single transaction in TableWriter. This will add the column of the new type, copy the data into it, drop the old column, and change the order of SELECT * columns in metadata.
• Support of the column type change in WAL writers
• Support of the column type update in WAL ILP writing pipelines