SQL is the dominant technology for accessing application data. It is increasingly becoming a performance bottleneck when it comes to scalability. Given its dominance, SQL is a crucial skill for all engineers.
An aggregate function is typically used in database queries to group together multiple rows to form a single value of meaningful data. A good programmer should be skilled at using data aggregation functions when interacting with databases.
Public questions (free account) are common interview questions. They are great for practicing, or if you want to filter candidates using the classic problems.
Given the following data definition, write a query that returns the number of students whose first name is John.
TABLE students id INTEGER PRIMARY KEY, firstName VARCHAR(30) NOT NULL, lastName VARCHAR(30) NOT NULL
- No students named John: Wrong answer
- Several students named John: Wrong answer
- Every student is named John: Wrong answer