When you receive the error “subquery returns more than 1 row,” it means that a subquery in your SQL query is returning multiple rows, but the SQL statement expects only one row to be returned. This can happen when you use a subquery in a SQL statement that uses a comparison operator like “=” or “<>”, which expects only one value on each side of the operator.
For example, consider the following query:
1 2 3 4 5 | SELECT name FROM students WHERE grade = (SELECT grade FROM students WHERE name = 'John') |
This query will return an error if more than one student has the same grade as John, because the subquery will return multiple grades, and the “=” operator expects only one grade on the right-hand side.
To fix this error, you can use a different comparison operator, such as “IN” or “ANY,” or you can modify the subquery to return only one row. Here’s an example using the “IN” operator:
1 2 3 4 5 | SELECT name FROM students WHERE grade IN (SELECT grade FROM students WHERE name = 'John') |
This query will return all students with the same grade as John, even if there is more than one student with that grade.
Alternatively, you could modify the subquery to return only one row using a function like “MAX” or “MIN”:
1 2 3 4 5 | SELECT name FROM students WHERE grade = (SELECT MAX(grade) FROM students WHERE name = 'John') |
This query will return the student(s) with the highest grade among all students named John.
