Correlated columns
Two columns of data, A and B of a single table, are correlated if the values in column A do not vary independently of the values in column B.
For example, the following
table is an excerpt from a large single table. Columns CITY and STATE
are highly correlated, and columns DEPTNO and SEX are entirely independent.
| CITY | STATE | DEPTNO | SEX | EMPNO | ZIPCODE |
|---|---|---|---|---|---|
| Fresno | CA | A345 | F | 27375 | 93650 |
| Fresno | CA | J123 | M | 12345 | 93710 |
| Fresno | CA | J123 | F | 93875 | 93650 |
| Fresno | CA | J123 | F | 52325 | 93792 |
| New York | NY | J123 | M | 19823 | 09001 |
| New York | NY | A345 | M | 15522 | 09530 |
| Miami | FL | B499 | M | 83825 | 33116 |
| Miami | FL | A345 | F | 35785 | 34099 |
| Los Angeles | CA | X987 | M | 12131 | 90077 |
| Los Angeles | CA | A345 | M | 38251 | 90091 |
In this simple example, for every value of column CITY
that equals 'FRESNO', the STATE column contains the same value ('CA'). 