SQL statement

INSERT

https://www.w3school.com.cn/sql/sql_insert.asp
INSERT INTO table_name ( Column 1, Column 2,…) VALUES ( value 1, value 2,…)

DELETE

https://www.w3school.com.cn/sql/sql_delete.asp
DELETE FROM The name of the table WHERE Column name = value

UPDATE

https://www.w3school.com.cn/sql/sql_update.asp
UPDATE The name of the table SET Column name = The new value WHERE Column name = Certain value

SELECT

https://www.w3school.com.cn/sql/sql_select.asp
SELECT Column name FROM The name of the table

Group query ：GROUP BY

The content to be queried in group query should be statistical information
SELECT (1) as a, mode ,COUNT(*) FROM t_help WHERE user_id = ‘060c43ee7c11437785bd8b35f72c0649’ GROUP BY mode

stay select in , You can put direct content ,eg: (1) as a, There can be another query in brackets ,
And grouped fields , You have to find it out in the front

The joint query ：LEFT JOIN

https://www.w3school.com.cn/sql/sql_join_left.asp
Through the common fields of the two tables , Jointly query all data
SELECT *
FROM table_name1
LEFT JOIN table_name2
ON table_name1.column_name=table_name2.column_name

Common aggregate functions ：

count() Count
sum() Sum up
avg() The average
max() Maximum
min() minimum value