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SQL statement
2022-07-03 02:31:00 【Python's path to immortality】
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
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