$2.$ Consider the following relational schema. An employee can work in more than one department; the pct$\_$time field of the Works relation shows the percentage of time that a given employee works in a given department.

Emp$($eid: integer, ename: string, age: integer, salary: real$)$

Works$($eid: integer, did: integer, pct$\_$time: integer$)$

Dept$($did: integer, budget: real, managerid: integer$)$

Write SQL$-92$ integrity constraints $($domain$,$ key, foreign key, or CHECK constraints; or

assertions$)$ or SQL:$1999$ triggers to ensure each of the following requirements, considered independently.

a$.$ Employees must make a minimum salary of $$20000$