SQL about GROUP by have experience (learn from other blogs)

Note: (Some problems that are found when practicing SQL statements are for informational and communication purposes only)

From where Gourpby have an

1.sql Basic execution sequence is: from >where>gourp by > have >orderby

(Having a filter that can be used for aggregate functions and groupings is generally used after group by, other and where no difference (self-understanding))

2. A GROUP BY experience! I understand the meaning is to group the table to display according to a field (what is displayed: The contents of the field are displayed differently)

Gourp by all multi-column grouping

Note: The field specified in select is either to be included in the group by statement, as a basis for grouping, or to be included in an aggregate function.

　　

function	function	support of
SUM (column name)	Sum
Max (column name)	Maximum Value
Min (column name)	Minimum value
AVG (column name)	Average
First (column name)	First record	Only access supports
Last (column name)	Last record	Only access supports
Count (column name)	Number of statistics records	Note the difference between the count (*) and

3. About having

SQL about GROUP by have experience (learn from other blogs)