Is your feature request related to a problem? Please describe.

Doris doesn't support decimal precision schema change operation now. It's hard for user to be sure of the precision at the beginning.

ALTER TABLE t MODIFY COLUMN c DECIMAL(20,2) KEY;

incubator-doris/fe/src/main/java/org/apache/doris/catalog/Column.java

Lines 281 to 283 in 81aa1c5

| | if (this.getPrecision() != other.getPrecision()) { |
| | thrownewDdlException("Cannot change precision"); |
| | } |