\subsection{Query Language}
The basic structure of a \sql\ statement is \texttt{SELECT I FROM T WHERE C},
which corresponds to $\Pi_{\texttt{I}}(\sigma_{\texttt{C}} \texttt{T})$.

We can set \texttt{I = *} if we want to return all columns for a table.
To rename, we can set \texttt{I = Column as Name, Column2 as Name2}, etc

% TODO: Make RA an acronym, too
\inlinetheorem Every SPJR RA expression can be written in \texttt{SELECT ... FROM ... WHERE ...} form:
\begin{tables}{lll}{Operation & Notation & SQL}
	Selection & $\sigma_c(R)$ & \texttt{SELECT * FROM R WHERE c;} \\
	Projection & $\Pi_{A_1, \ldots, A_n} R$ & \texttt{SELECT A1, \ldots, An FROM R;} \\
    Cartesian Product & $R_1 \times R_2$ & \texttt{SELECT * FROM (R1, R2);} \\
    Rename & $\rho_{a, b, c} R$ & \texttt{SELECT A as a, \ldots, B as c FROM R;} \\
    Union & $R_1 \cup R_2$ & \texttt{R1 UNION R2;} \\
    Difference & $R_1 - R_2$ & \texttt{R1 EXCEPT R2;} \\
    Intersection & $R_1 - R_2$ & \texttt{R1 INTERSECT R2;} \\
\end{tables}
Since \sql\ implements bag and not set semantics, there is a \texttt{DISTINCT} keyword, which is used to remove duplicates.

For the last three operations, \texttt{R1} and \texttt{R2} typically are other \sql\ statements:
\mint{sql}|(SELECT name FROM FirstTable) UNION (SELECT name FROM SecondTable)|