How Oracle makes data type changes to columns with data

Two methods:

Method one, by backing up the table

1. Create a backup table

CREATE TABLE T_bak as SELECT * FROM t

2. Change the corresponding column data type after deleting the original table data

Delete from T

3. Import the data from the backup table into the original table

INSERT INTO t select * from T_bak

4. Deleting a backup table

Method two, by backing up the column

1. Modify the original column named Col_tmp

2. Create a backup column col (the data type that needs to be changed and is nullable)

3. Update the data from the original column to the backup column

Update T set Col=trim (COL_TMP);

4. Delete the original column col_tmp

How Oracle makes data type changes to columns with data