SQL Oracle, what is done here?

Question

Can someone telle me what this code exactly does? What does the 4 mean after count-function?

SELECT ROUND(SUM(correct)/COUNT(*),4) AS accuracy
  FROM (SELECT DECODE(survived,
               PREDICTION(DT_TITANIC USING *), 1, 0) AS correct
          FROM titanic_test_data);

It is the second argument to `ROUND()` and no doubt the simplest part of the query. — Gordon Linoff, Aug 05 '21 at 11:29
It's rounding to 4 decimal places. See https://docs.oracle.com/cd/B19306_01/server.102/b14200/functions135.htm — The Impaler, Aug 05 '21 at 11:52

score 0 · Answer 1 · answered Aug 05 '21 at 13:04

What does it do? Calculates an average and rounds it to 4 decimals.

SQL> select sum(sal) sum_salary,
  2         count(*) num_of_employees,
  3         --
  4         sum(sal) / count(*) average_salary,
  5         --
  6         round(sum(sal) / count(*), 4) rounded_avg_salary
  7  from emp;

SUM_SALARY NUM_OF_EMPLOYEES AVERAGE_SALARY ROUNDED_AVG_SALARY
---------- ---------------- -------------- ------------------
     29025               14     2073,21429          2073,2143

sum_salary is sum of all salaries in the table
num_of_employees is number of employees
average_salary, as sum_salary divided by num_of_employees
rounded_avg_salary is what "your" code does

Note that we usually do it as

SQL> select avg(sal) from emp;

  AVG(SAL)
----------
2073,21429

SQL Oracle, what is done here?

1 Answers1