DBMS (2nd Ed.) By RaghuramKrishnan #Page no:128 and 129

Question

Find SQL :-

(Q17) Compute increments for the ratings of persons who have sailed two different boats on the same day.

(Q18) Find the ages of sailors whose name begins and ends with B and has at least three characters.

Comments

18. select age from sailor where sname like 'B__%B;

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Can u plz explan 'B__%B;

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Here are some examples showing different LIKE operators with '%' and '_' wildcards:

LIKE Operator    Description
WHERE CustomerName LIKE 'a%'    Finds any values that starts with "a"
WHERE CustomerName LIKE '%a'    Finds any values that ends with "a"
WHERE CustomerName LIKE '%or%'    Finds any values that have "or" in any position
WHERE CustomerName LIKE '_r%'    Finds any values that have "r" in the second position
WHERE CustomerName LIKE 'a_%_%'    Finds any values that starts with "a" and are at least 3 characters in length
WHERE ContactName LIKE 'a%o'             Finds any values that starts with "a" and ends with "o"
 WHERE ContactName LIKE'B__%B'            Begins and ends with B and has at least three characters

 Now, you will get it.

Answer 1

For first question....

1.SELECT rating+1 FROM Sailor WHERE sid IN (SELECT sid FROM R2 GROUP BY date,sid HAVING COUNT(*)=2)

and for second....

 @akash.dinkar12 comments

Answer 2

Q18> select S.age from sailors S where sname LIKE 'b_%b';

NOTE: if asked atleast 2 characters = 'b%b'  , if asked exactly 3 characters, 'b_b'