According to the relational model students (student number, name, gender, date of birth), the query gender is "male", sorted by age from small to large.

According to the students (student number, name, gender and date of birth) of the relational model, the query gender is "male", and the order is: select * from students where gender = "male" order by date of birth DESC.

The older the date of birth, that is, the later the birth, the younger the age, so if you want to sort the age from small to large, you should sort the date of birth from big to small.

Extended data

The relational schema can be formally expressed as: R(U, d, dom, f). Where, R is the relationship name, U is the set of attribute names that make up the relationship, D is the domain from which the attributes in the attribute group U come, dom is the mapping set from attributes to domains, and F is the data dependency set between attributes.

Usually abbreviated as: R(U) or R(A 1, A2…An), where r is the relationship name, u is the set of attribute names, A 1, A2…An is each attribute name.

The integrity of the relationship is a constraint on the relationship. There are three situations:

1, entity integrity: The primary attribute cannot be empty, which ensures the uniqueness of each tuple.

2. Reference integrity rules: As follows, the foreign code value in P can only be empty or the main code value in C. ..

3. User-defined integrity: user sets constraints, such as the attribute cannot be empty. The latter two are supported by all database systems, while user-defined integrity is user-defined.