protected void convert(DecimalColumnVector outputColVector, DecimalColumnVector inputColVector, int i) {
    // The set routine enforces precision and scale.
    outputColVector.set(i, inputColVector.vector[i]);
  }
Convert input decimal value to a decimal with a possibly different precision and scale,
at position i in the respective vectors.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/CastDecimalToDecimal.java