@Override
  @Explain(displayName = "columnExprMap", jsonOnly = true)
  public Map<String, String> getColumnExprMapForExplain() {
    if(this.reversedExprs == null) {
      return super.getColumnExprMapForExplain();
    }
    Map<String, String> explainColMap = new HashMap<>();
    for(String col:this.colExprMap.keySet()){
      String taggedCol = this.reversedExprs.get(col) + ":"
          + this.colExprMap.get(col).getExprString();
      explainColMap.put(col, taggedCol);
    }
    return explainColMap;
  }
Get the string representation of filters.

Returns null if they are no filters.

@return Map from alias to filters on the alias.
ql/src/java/org/apache/hadoop/hive/ql/plan/JoinDesc.java