Created: 2022-08-02
Tags: #fleeting
Allows you to summarize information about a group of rows of data.
Select query with aggregate functions over all rows
SELECT AGG_FUNC(column_or_expression) AS aggregate_description, …
COUNT(*)
Counts the number of rows in the group if no column name is specified.
COUNT(column)
Count the number of rows in the group with values in the specified column.
MIN(column)
Finds the mininum num value
-> in the specified column for all rows in the group.
MAX(column)
Finds the maximum num value
-> in the specified column for all rows in the group.
AVG(column)
Finds the average num value
-> in the specified column for all rows in the group.
SUM(column)
Finds the sum of all num values
-> in the specified column for the rows in the group.
Without a specified grouping,
-> each aggregate function is going to run on the whole set of result rows and return a single value.
GROUP BY clause in aggregate expressions
Only use this when there is an aggregate functions/expressions in query. query in sql explained
You can use GROUP BY to select a specific data when using functions.
Select query with aggregate functions over groups
SELECT AGG_FUNC(column_or_expression) AS aggregate_description, …
FROM mytable
WHERE constraint_expression
GROUP BY column;
HAVING clause allows us to group the results of GROUP BY clause
It's just an additional way to filter an already filtered data
WHERE condition <- This is not entirely needed to have "having"
GROUP BY column
HAVING group_condition;