Oracle modifies the data type of an existing column

Oracle cannot modify the data type of an existing column if there is data in the table. However, you can create a temporary column, copy the data of the column to the temporary column, delete the original column, and modify the name of the temporary column. In this case, it seems a bit confusing. Let's explain it step by step. The table "AC_REG" has a column: is_active, which is originally of the character type. The goal is to change it to the numerical type.

--- Change IS_ACTIVE to numeric. -- add an alter table AC_REG add is_active_temp number (1); -- change the value of IS_ACTIVE, assign is_active_tempupdate AC_REG set is_active_temp = cast (is_active as number (1); -- delete the original alter table AC_REG drop column is_active; -- modify the name alter table AC_REG rename column is_active_temp to is_active;