Question

Relational algebra pls. Appreciate it！(Queries are detailed)

Consider the following relational database that stores information about bars and customers: Drinker (name, address) Bar (name, address) Beer (name, brewer) Frequents (drinker, bar, times a week) Likes (drinker, beer) Serves (bar, beer, price) Write the following queries in relational algebra:

Answer 1

Answer is as follows :

Relational Algebra for given scenarios are :

Answer 1 :

In this we get to know that we need four tables i.e. Drinker, Likes, Frequents and Servers.

Drinker is used to get data about drinker, Likes defines the beer he/she likes, Frequents finds the corresponding bar and servers helps to find the only corresponding bars.

$\prod$_{drinker.name, drinker.address} ( Drinker $\Join$ Likes $\Join$ Frequents $\Join$ Serves) $\sigma$ _{drinker.name = likes.drinker $\wedge$ likes.drinker = frequents.drinker $\wedge$ frequents.beer = servers.beer} ;

Answer 2 :

In this we get to know that we need four tables i.e. Drinker, Likes, Frequents

Drinker is used to get data about drinker, Likes defines the beer he/she likes, Frequents finds the corresponding bar. For every bar details, we get bar names form frequents table too.

$\prod$_{drinker.name, drinker.address} ( Drinker $\Join$ Likes $\Join$ Frequents) $\sigma$ _{drinker.name = likes.drinker $\wedge$ likes.drinker = frequents.drinker} ;

Answer 3 :

In this we need only two tables i.e. Drinker and Likes and Frequents

Drinker is used to get data about drinker and Likes to find the which beer drink by Amy. Frequents used to find same match of same beers which liked by Amy.

$\prod$_{drinker.name, drinker.address} ( Drinker $\Join$ Likes ) $\sigma$ _{likes.drinker = "Amy" $\wedge$ likes.beer = frequents.drinker} ;

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