Semijoin. Consider the relational database schema concerning magazines subscribed by students at Midland Institute of Technology: student(s-name, SID, address, major, GPA) subscribes(s-name, m-name, start date) magazine(m-name, publisher, mtype, price) Note: Attributes s-name and m-name indicate student names and magazine names, respectively. Attribute m-type indicates magazine types (e.g. C for computer-related, S for sports, etc.) Start.date is an attribute indicate the start date of subscribing a magazine. Price indicates annual subscription rate. (a) Write an RA query using the semijoin operator: Find the major and GPA for any student who subscribed a magazine which costs $20 per year (b) Revise the block nested join algorithm to implement semioin, Show the revised pseudocode. [Hint: Think about this: Semijoin is a theta join (or natural join) followed by project operation. But do we need to execute these two steps separately?]