Constraints

A constraint object represents a table or column constraint on the database.

SQLEditor supports UNIQUE and CHECK constraints.

A UNIQUE constraint requires that the value in the specified column must be unique within the table.

If multiple columns are specified then each specific combination of values must be unique

For example, if the constraint was

UNIQUE(name,birthday,shoeSize)

then each row would have to have a different value for the the combination of name,birthday and shoe size.

row	name	birthday	shoeSize
1	joe	01/01/1900	10
2	fred	01/01/1990	9

But the following row would be rejected if we tried to insert it.

row	name	birthday	shoeSize
3	joe	01/01/1900	10

Because it has the same (name,birthday,shoeSize) combination as row 1

A CHECK constraint specifies a particular expression that must be satisfied

An example might be that prices must be greater than zero. This would be expressed as follows:

CHECK(price > 0)

Any price value that wasn't above 0 would then be rejected by the database.

Support for constraints is database specific and some databases don't support CHECK constraints at all

Constraints are edited using the inspector.

Constraints at the table level use the constraint inspector panel.

Use the Unique Checkbox in the field inspector

Use the Check Constraint subpanel of the field inspector