A unary relationship is a relationship between the rows of a single table. For example, if all of your known relatives are stored in a table named tblFamily, then you can represent the "mother" relationship as a unary relationship. Each record in the table will have a pointer (foreign key) to the record of their mother. Of course, the oldest known relatives in the table will have null values for their own mothers.
| ID | Name | Born | MotherID |
| 100 | Willaim | 1848 | -- |
| 101 | Abigail | 1850 | -- |
| 102 | Thomas | 1869 | 101 |
| 103 | Robert | 1873 | 101 |
| 104 | Sally Anne | 1876 | 101 |
| 105 | Susan | 1899 | 104 |
| 106 | George | 1901 | 104 |
| 107 | Georgia | 1901 | 104 |
| 108 | Libby | 1919 | 105 |
| 109 | Richard | 1922 | 105 |
| 110 | Allan | 1922 | 107 |
| 111 | Hazel | 1924 | 107 |
| 112 | Linda | 1929 | 105 |
| 113 | Larry | 1942 | 108 |
| 114 | Curly | 1944 | 108 |
| 115 | Moe | 1946 | 108 |
| 116 | Betty | 1952 | 112 |
| 117 | Anthony | 1953 | 108 |
| 118 | John | 1954 | 111 |
| 119 | Jean | 1957 | 112 |
| 120 | Edward | 1959 | 111 |
| 121 | Lucy | 1969 | 116 |
| 122 | Andrew | 1973 | 116 |
| 123 | Jim Bob | 1980 | 119 |
Unary relationships, though not as common as binary relationships, do have many practical applications. They can be used to represent product subassemblies (e.g., part X is used as a component of part Y which is then used to make part Z). Unary relationships can be used to represent precedent conditions (e.g., MIS 304 and MIS 325 are prereqs MIS 333K). They can also be used to represent a boss-worker relationship (e.g., Susan Smith is John Jones' boss).