The ALTER TABLE.. ADD COLUMN statement adds a column to an existing table. This operation is online in TiDB, which means that neither reads or writes to the table are blocked by adding a column ...

If a column is already in the table, you can change the following column attributes using the MODIFY clause: length, informat, format, and label. The values in a table are either truncated or padded ...

Specifies whether the column can accept NULL values. Columns that do not allow NULL values can be added only if they have a default specified. If the new column allows NULL values and no default is ...