oracle sql rank dense_rank row

測試表emp

RANK

SQL> select EMPNO,DEPTNO,SAL,
2 rank()over(partition by DEPTNO order by SAL) "rank"
3 from emp;

EMPNO     DEPTNO         SAL       rank
---------- ---------- ---------- ----------
      7934        10         1300      1
      7782        10         2450      2
      7839        10         5000      3
      7369        20           800      1
      7876        20         1100      2
      7566        20         2975      3
      7788        20         3000      4
      7902        20         3000      4
      7900       30          950      1
      7654       30        1250      2
      7521       30        1250      2
      7844       30        1500      4
      7499        30         1600      5
      7698        30         2850      6

14 rows selected.

按照deptno分組sal升序排列，這裡注意到deptno=30的sal=1250的兩個僱員，並列在該組中排名第2。然後下一個就是第4名。

What we see here is where two people have the same salary they are assigned the same rank. When multiple rows share the same rank the next rank in the sequence is not consecutive

如果兩個人有相同的salary，就分配相同的排名。多行共享了相同的排名之後，下一個排名在順序上是不連續的。

要和後面的dense_rank(),row_number()區分。

DENSE_RANK

The DENSE_RANK function acts like the RANK function except that it assigns consecutive ranks.

DENSE_RANK函數和RANK函數相似，如果有多個人有相同的salary，會分配same rank，不同之處在于下一個排名在順序上是連續的。

SQL> select EMPNO,DEPTNO,SAL,
2 dense_rank()over(partition by DEPTNO order by SAL) "rank"
3 from emp;
     EMPNO     DEPTNO         SAL       rank
---------- ---------- ---------- ----------
      7934        10         1300      1
      7782        10         2450      2
      7839        10         5000      3
      7369        20           800      1
      7876        20         1100      2
      7566        20         2975      3
      7788        20         3000      4
      7902        20         3000      4
      7900        30           950      1
      7654       30        1250      2
      7521       30        1250      2
      7844       30        1500      3
      7499        30         1600      4
      7698        30         2850      5

14 rows selected.

ROW_NUMBER

row_number函數的區別在於，當多個人有相同的salary的時候并不會共享rank，而是連續的分配rank。not same rank,not consecutive

SQL> select EMPNO,DEPTNO,SAL,
2 row_number()over(partition by DEPTNO order by SAL) "rank"
3 from emp;
     EMPNO     DEPTNO         SAL       rank
---------- ---------- ---------- ----------
      7934       10        1300      1
      7782       10        2450      2
      7839       10        5000      3
      7369       20         800       1
      7876       20        1100      2
      7566       20        2975      3
      7788       20        3000      4
      7902       20        3000      5
      7900       30         950       1
      7654       30        1250      2
      7521       30        1250      3
      7844       30        1500      4
      7499       30        1600      5
      7698       30        2850      6

14 rows selected.

FIRST and LAST

The FIRST and LAST functions can be used to return the first or last value from an ordered sequence

用於返回first 或者last value

SQL> select EMPNO,DEPTNO,SAL,
2 min(sal)keep(dense_rank first order by sal )over(partition by DEPTNO) "Lowest",
3 max(sal)keep(dense_rank last order by sal )over(partition by DEPTNO) "Highest"
4 from emp;
     EMPNO     DEPTNO         SAL     Lowest    Highest
---------- ---------- ---------- ---------- ----------
      7782       10        2450       1300      5000
      7839       10        5000       1300      5000
      7934       10        1300       1300      5000
      7566       20        2975         800      3000
      7902       20        3000         800      3000
      7876       20        1100         800      3000
      7369       20         800          800      3000
      7788       20        3000         800      3000
      7521       30        1250         950      2850
      7844       30        1500         950      2850
      7499       30        1600         950      2850
      7900       30         950          950      2850
      7698       30        2850         950      2850
      7654       30        1250         950      2850

14 rows selected.

下面這種寫法，返回結果和上面一樣。
SQL> select EMPNO,DEPTNO,SAL,
2 min(sal)over(partition by DEPTNO) "Lowest",
3 max(sal)over(partition by DEPTNO) "Highest"
4 from emp;
     EMPNO     DEPTNO         SAL     Lowest    Highest
---------- ---------- ---------- ---------- ----------
      7782       10        2450       1300      5000
      7839       10        5000       1300      5000
      7934       10        1300       1300      5000
      7566       20        2975         800      3000
      7902       20        3000         800      3000
      7876       20        1100         800      3000
      7369       20         800          800      3000
      7788       20        3000         800      3000
      7521       30        1250         950      2850
      7844       30        1500         950      2850
      7499       30        1600         950      2850
      7900       30         950          950      2850
      7698       30        2850         950      2850
      7654       30        1250         950      2850

14 rows selected.

2016-04-13