Oracle : select maximum value from different columns of the same row

Given this test data …

SQL> select *
  2  from your_table
  3  /

NAME         M1         M2         M3         M4
---- ---------- ---------- ---------- ----------
A             1          2          3          4
B             6          3          4          5
C             1          5          2          1

SQL>

… a straightforward GREATEST() call will give the desired result:

SQL> select name
  2          , greatest(m1, m2, m3, m4) as the greatest_m
  3  from your_table
  4  /

NAME THE_GREATEST_M
---- --------------
A                 4
B                 6
C                 5

SQL>

Note that greatest() will return NULL if any of the arguments are null. If this is a problem then use nvl() to provide a default value which won’t distort the outcome. For instance, if no values can be negative….

SQL> select name
  2          , greatest(nvl(m1,0), nvl(m2,0), nvl(m3,0), nvl(m4,0)) as the greatest_m
  3  from your_table
  4  /

NAME THE_GREATEST_M
---- --------------
A                 4
B                 6
C                 5

SQL>

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