diff --git a/semester4/dmdb/data-modelling-databases-summary.pdf b/semester4/dmdb/data-modelling-databases-summary.pdf
index ff135d3..590d4cb 100644
Binary files a/semester4/dmdb/data-modelling-databases-summary.pdf and b/semester4/dmdb/data-modelling-databases-summary.pdf differ
diff --git a/semester4/dmdb/parts/01_sql/03_query-language/00_intro.tex b/semester4/dmdb/parts/01_sql/03_query-language/00_intro.tex
index e69de29..0f2d228 100644
--- a/semester4/dmdb/parts/01_sql/03_query-language/00_intro.tex
+++ b/semester4/dmdb/parts/01_sql/03_query-language/00_intro.tex
@@ -0,0 +1,22 @@
+\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)|
diff --git a/semester4/dmdb/parts/01_sql/main.tex b/semester4/dmdb/parts/01_sql/main.tex
index 58403be..d67d343 100644
--- a/semester4/dmdb/parts/01_sql/main.tex
+++ b/semester4/dmdb/parts/01_sql/main.tex
@@ -3,5 +3,7 @@
 \input{parts/01_sql/00_intro.tex}
 \input{parts/01_sql/01_ddl.tex}
 \input{parts/01_sql/02_dml.tex}
+\input{parts/01_sql/03_query-language/00_intro.tex}
+
 \input{parts/01_sql/01_operations.tex}
-% \input{parts/00_sql/}
+% \input{parts/01_sql/}