Single table query
Complete grammar
Simple query
Filter conditions before grouping in where
Group by grouping
What is grouping: categorized according to the same parts of all records, certain fields with low discrimination
Why grouping: when we want to count on a group basis, we have to group.
The purpose of grouping is to make statistics on a group basis, and then to consider that a single record is meaningless.
Aggregate function
Usage
Having is further screened for the results of the aggregation after the aggregation.
Order by sorting
Conditions under which limit restricts display
Regular expression
