If you want to increase the length of a column from varchar (100) to varchar (102) it will alter the column length, but, if you want to reduce the length of the column using ADD in Alter command, it gives an Error :3558.
- For decimal field alteration, The alter table will work for field limit on byte size. Like Altering column length from DECIMAL(5,0) - DECIMAL(9,0) is possible but altering column length from DECIMAL(9,0) - DECIMAL(26,0) is not possible , Below is the chart for permissible value and the space in byte which a decimal occupies.
|Number of Digits||Number of Bytes|
|1 to 2||1|
|3 to 4||2|
|5 to 9||4|
|10 to 18||8|
|19 to 38||16|