Write the data definition statements of SQL that modify the structures and$/$or constraints of a

database listed on a page $4$ of the examination paper in the way described below.

Note that some of the modification may require more than one data definition statements of SQL

statement.

$(1)$ Modify a structure and consistency constraint of the sample database such that after a

modification it is possible to record in the database information about the balance of an account

that is non$-$negative and not larger than $99999999\mathrm{.}99.$

$(2)$ Modify a structure and consistency constraint of the sample database such that after a

modification, it is possible to store in the database information about the total number of

branches for each bank. The total number of branches is a non$-$negative integer not larger than

$999.$

$(3)$ Modify a consistency constraint of a sample database such that after a modification, the

employee$$s first name, last name, and date of birth can identify an employee.

$(4)$ Modify a structure of a sample database such that after a modification, it is possible to store in

the database the phone number of each bank. Assume that the phone number is no longer than $16$ digits $16.$

$(5)$ Modify a structure of a sample database such that after a modification, the first name and last

name are no longer than $30$ characters each