1SET OPERATION
A type of operations which allow the results of multiple queries to be combined into a single result set.
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UNION
Is used to combine the results of two or more SQL query blocks.
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INTERSECT
Is used to combine only those rows which the results of two query blocks have in common.
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EXCEPT
It combines results of two SELECT statements and return only those in the final result, which belongs to the first set of the result.
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AGGREGATION FUNCTIONS
These are functions that take a collection (a set or multiset) of values as input and return a single value.
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NULL VALUES
It is a field with no value and it complicates the processing of aggregate operators.
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BOOLEAN DATA TYPE
It can take values true, false, and unknown. On and off are synonyms for true and false, while unknown is identical to the null constant.
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GROUP BY
is used to apply the aggregate function not only to a single set of tuples, but also to a group of sets of tuples.
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HAVING
is used to state a condition that applies to groups rather than to tuples.
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Count
The number of (unique) values in the A column.
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Sum
The sum of all (unique) values in the A column.
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AVG
The average of all (unique) values in the A column.
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Min
The minimum value in the A column.
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Max
The maximum value in the A column.