Constraint types
| Constraint | Definition | Purpose |
|---|---|---|
| Primary Key | Uniquely identifies each row. Can’t be null. Only one per table. | Use for identifying records and establishing relationships between tables. |
| Unique | All values must be different. Can allow NULL values (behavior varies by database). | Prevents duplicate data without being the primary identifier. |
| Unique* | Combination of multiple columns must be unique (hover to see which columns). Individual column values can repeat. | Enforces uniqueness on combinations of data, such as first and last name together. |
| Not null | Column must always contain a value. Can’t be empty. | Ensures critical data is always present. |
Columns with Primary Key or Unique constraints make good candidates for join operations in pipelines.