:PROPERTIES: :ID: 5f12c4b1-8767-43ee-94cc-a1bd2cd5b23a :mtime: 20231024033232 :ctime: 20231024033210 :END: #+title: SQL #+filetags: :public:project: * SQL In the context of databases, SQL is a programming language based on [[id:d38dac96-015e-4386-873c-3a1e16911ef2][relational algebra]]. * [[id:d38dac96-015e-4386-873c-3a1e16911ef2][Relational Algebra]] vs [[id:5f12c4b1-8767-43ee-94cc-a1bd2cd5b23a][SQL]] [[id:5f12c4b1-8767-43ee-94cc-a1bd2cd5b23a][SQL]] is based on Relational Algebra | Relational Algebra | [[id:5f12c4b1-8767-43ee-94cc-a1bd2cd5b23a][SQL]] | |--------------------+----------------------------| | $\sigma_p(Q)$ | SELCT * FROM $Q$ WHERE $p$ | | $\pi_x(Q)$ | SELECT $x$ from $Q$ | | $\rho_M(Q)$ | SELECT AS $M$ from $Q$ | | $Q_1 \cup Q_2$ | $Q_1$ UNION $Q_2$ | | $Q_1 \cap Q_2$ | $Q_1$ INTERSECT $Q_2$ | | $Q_1 - Q_2$ | $Q_1$ EXCEPT $Q_2$ | | $Q_1 \times Q_2$ | $Q_1$ , $Q_2$ |