Aggregates (like methods)

Count

Number of rows

SELECT COUNT(*)
FROM SchemaName.TableName

Number of rows where the value of colName is not null

SELECT COUNT(colName)
FROM SchemaName.TableName

Number of unique values for colName

SELECT COUNT(DISTINCT colName)
FROM SchemaName.TableName

Group By

The moment you want to introduce another column like colName, then you MUST use group by!

Count of the number of rows for each unique colName value

SELECT 
	colName,
	COUNT(*)
FROM SchemaName.TableName
	GROUP BY colName

Sum

Adds up all values for a certain column

SELECT SUM(Id)
FROM SchemaName.TableName

Avg

Gets the mean of all values for a certain column

SELECT AVG(Id)
FROM SchemaName.TableName

Max

Largest value of all rows

SELECT MAX(Id)
FROM SchemaName.TableName

Min

Smallest value of all rows

SELECT MIN(Id)
FROM SchemaName.TableName