MySQL Learning Path (v) MySQL advanced query

MySQL statistics function

Count (): Statistic quantity;

Max (): Statistical maximum;

Min (): Minimum statistical value;

AVG (): Statistical averages;

SUM (): statistics and;

Select Count (* from student;

MySQL sort group by;

The default is ascending sort;

Select *  fromStudentGroup  bySidASC;--Sort AscendingSelect *  fromStudentGroup  bySidDESC;--Sort DescendingSelect *  fromStudentGroup  bySid,sname;---Multi-field sorting

Having the same use method and where, the function is more powerful than where;

Limit limit Query

Limit queries a specified number of data in a data table

Limit can only limit the query

Mainly used to achieve paging effect;

Select *  from 1 ; -- Query 1 Data Select *  from 1,2; -- starting from subscript 1 to query two data;

MySQL connection query

Cross joins: Crosses join; loops out each record from a table, each record is connected to another table;

Connection mode: Left table cross join right table;

Inner joins: Left table inner join right table on condition;

Alias: As (can save As)

External links: outer join;

Outer LEFT join;

outer right join;

Select *  fromStudent Cross JoinStudent2;Select *  fromStudentInner JoinStudent2 onStudent.sid=Student2.sid;Select *  fromStudent asAInner JoinStudent2 b onA.sid=B.sid;Select *  fromStudent asA Left outer JoinStudent2 b onA.sid=B.sid;Select *  fromStudent asA Right outer JoinStudent2 b onA.sid=B.sid;

Multi-Table Query Union (ALL;DISTINCT)

All: Do not go to the weight, keep all the data;

Distinct: Remove weight (default);

MySQL Learning Path (v) MySQL advanced query