1. The database is generally used as a storage function, and generally does not require function operations
2. Insert multiple pieces of data at a time
3. The method of inserting data into the table:
insert into story_wangjing(id,name) values (1,’wangjing’);
insert into story_wangjing values(2,’lisi’);
insert into story_wangjing values(3,’zhao’),(4,’haha’),(5,’jj’);
4. Modify multiple values at once
5. The data method of the five middle school:
(1) Manual
(2) Jmeter , loadrunner, page pressure test
(3) Operate the database and use Python to insert data into the table
(4) Datafactory tools
(5) Stored procedure (for a single table, the efficiency is the fastest. If the table is related, it is not easy to use if it is more complicated. All logical relationships, foreign keys, and primary keys must be handled)
6. Commonly used functions in Sql query:
（1） select count(*) from story_wangjing;
（2） select avg(id) from story_wangjing;
（3） select sum(id) from story_wangjing;
（4） select max(id) from story_wangjing;
（5） select min(id) from story_wangjing;
7. Grouping + Calculation
8. Grouping + Average
9. After grouping, find a specific field with having
10. Query the author information of all authors who have appeared in book_wangjing
11. Query all mr.jackson information
12. Left join:
13. Right join:
14. Inner join: a.author_name and b.book_author appearing in the result set must exist in both tables at the same time
15. Left join: a.author_name appearing in the result set must exist in the left table (author_wangjing table) and display all
16. Right join: b.book_author that appears in the result set must exist in the right table (book_wangjing table) and display all
17. union : For merging, when using union, the data columns of the coordinates should be as many as the data columns of the right table
18. Calculate the current time:
19. Tomorrow:
20. Yesterday
26. Format reference
Interval Name Description
Second seconds
Minute _
Hours _
Day _
Month _
Year _
Minute_second minutes and seconds, separated by ":"
Hour_second hours, minutes and seconds, separated by ":"
Year_month year and month, separated by "-"
27. Reduce time:
