My question is on the working of OR operator in SQL, can it be used to combine two selection queries-CodePudding

SELECT student.name 
FROM student
WHERE student.email = copy.owner AND copy.book = "978-0262033848" 
OR
SELECT student.name 
FROM student
WHERE student.email = loan.borrower AND loan.book = "978-0262033848";

In this code, I tried to combine two queries. It is displaying an error and I would like to know what is the mistake in using it this way

CodePudding user response：

My best guess is that this does what you want:

SELECT s.name
FROM student s
WHERE EXISTS (SELECT 1
              FROM copy c
              WHERE c.email = c.owner and c.book = '978-0262033848'
             ) OR
      EXISTS (SELECT 1 
              FROM loan l
              WHERE s.email = l.borrower and l.book = '978-0262033848'
             );

This select students that are in the loan or copy tables with the specified book.