• $x ∈ π_X(Q): ∀ y ∈ S: (x, y) ∈ Q$

• $(x, z) ∈ π_X(Q) × π_Z(S): ∀ y ∈ π_Y(σ_{Z=z}(S)): (x, y) ∈ Q$

select distinct A1, A2, …, An from R

select A1, A2, …, An from R 
   -- с повторениями

select * from R where Condition

select …, b as a, … from R

select * from R1 union select * from R2

select * from R1 union all select * from R2
    -- с повторениями

select * from R1 intersect select * from R2

select * from R1 intersect all select * from R2
    -- с повторениями

select * from R1 except select * from R2

select * from R1 except all select * from R2
    -- с повторениями

select *, expr as A from R

select X, Function(A) as A from R group by X

select count(*) … -- подсчет всех

select count(distinct A) … -- подсчет различных

select count(q) … -- подсчет не null

… having condition -- фильтрация после агрегации

… order by attrs -- сортировка

select * from R1 cross join R2

select * from R1, R2

select * from R1 natural join R2

select * from R1 inner join R2 using (A)

select * from R1 inner join R2 on R1.A = R2.A

select * from R1 inner join R2 on θ

select * from R1 full [outer] join R2 using (...)

select * from R1 full [outer] join R2 on θ

select * from R1 left [outer] join R2 using (...)

select * from R1 left [outer] join R2 on θ

select * from R1 right [outer] join R2 using (...)

select * from R1 right [outer] join R2 on θ

select [distinct]
    … as …, … as … -- ε, π и ρ
from
    R1 A1
    ххх join R2 A2 on …   -- ⊗
    …
    ххх join Rn An on …   -- ⊗
where
    … -- σ