DEFAULT Column Constraint
Column constraint to set a default value for the specified column
A constraint is used to define rules that help to provide data integrity. Column constraints are specific to the column name specified. You must have ALTER privilege on the table. The table will be locked for EXCLUSIVE use during the operation.
The DEFAULT column constraint is used to set a default value for the specified column. The <expr> must evaluate to the same data type as the target column. The column's value can subsequently be updated.
ALTER TABLE customer; ADD COLUMN dateref DATE DEFAULT date()