public void operatorConcatSql(HplsqlParser.Expr_concatContext ctx) {
    StringBuilder sql = new StringBuilder();
    sql.append("CONCAT(");
    int cnt = ctx.expr_concat_item().size();
    for (int i = 0; i < cnt; i++) {
      sql.append(evalPop(ctx.expr_concat_item(i)).toSqlString());
      if (i + 1 < cnt) {
        sql.append(", ");
      }
    }
    sql.append(")");
    Var var = new Var(Type.SQL_STRING, sql);
    exec.stackPush(var);
  }
String concatenation operator in executable SQL statement
hplsql/src/main/java/org/apache/hive/hplsql/Expression.java