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[DMDB] Some notes

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Janis Hutz
2026-02-28 18:04:32 +01:00
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semester4/dmdb/parts/00_sql/01_operations.tex Normal file
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\begin{tables}{ll}{Keyword & Description}
\texttt{SELECT val, val2} & returns the columns \texttt{val} and \texttt{val2} \\
\texttt{FROM table d, table2 c} & selects the target tables. Can use range variables (\texttt{d, c} here) \\
\texttt{WHERE} & Filter results. Can also target non-acquired columns \\
\texttt{DISTINCT} & Returns elements without duplicates \\
\texttt{UNION} & Set union (also removes duplicates) \\
\texttt{INTERSECT} & Set intersection \\
\texttt{EXCEPT} & Set difference \\
\texttt{JOIN} & Join tables, always requires a ON clause \\
\texttt{DATE} & Used to do comparisons against fixed Dates (followed by Datesting) \\
\texttt{AVG(column)} & Computes the average of the specified column \\
\texttt{SUM(column)} & Computes the sum of the specified column \\
\end{tables}
We can directly add new columns to our result using statements like (also note that we do not actually return salary and employment columns)
\mint{sql}{SELECT name, salary * employment / 100 AS RealSalary FROM employees;}