Write the data definition statements of SQL that modify the structures of a database listed on a page $2$ of the

examination paper such that after the modifications the following data manipulations are possible.

$(1)$ It should be possible to add to the database information about the present employer of each applicant.

$(2)$ It should be possible to store in the database information about the courses passed by each applicant;

assume that an applicant passes zero or more courses and each course is described by a unique

name, no more than $30$ characters long.

$(3)$ It should be possible to store information about the types of position offered by the employer; assume

that a type of position is either "admin" or "production" or "security".

$(4)$ It should be possible to skip information about phone number when entering data of a new applicant or

modifying data of already recorded applicant.

$(5)$ The skill level that possessed by an applicant and needed for a position can be a positive integer that up

to $10.$