Update of SQL

1. Summary of ways to modify records:

• Set to new value: UPDATE table_name SET column_name=new_value [, column_name2=new_value2] [WHERE column_name3=value3]
• Replace according to the existing value: UPDATE table_name SET key1=replace(key1, 'Find content', 'Replace with content') [WHERE column_name3=value3]

2. Case

(1) There is an examination paper information table examination_info, the table structure is shown in the following figure:

Filed	Type	Null	Key	Extra	Default	Comment
id	int(11)	NO	AT	auto_increment	(NULL)	auto-increment ID
exam_id	int(11)	NO	UNI		(NULL)	paper ID
tag	char(32)	YES			(NULL)	category label
difficulty	char(8)	YES			(NULL)	difficulty
duration	int(11)	NO			(NULL)	duration
release_time	datetime	YES			(NULL)	release time

--t1:
update examination_info
set tag = replace(tag,'PYTHON','Python')
where tag = 'PYTHON';

--t2:
update examination_info
set tag = 'Python'
where tag = 'PYTHON';

Please change all the tag fields tagged PYTHON in the examination_info table to Python.

(2) There is an examination paper answer record table exam_record, which contains user answer paper records for many years, and the structure is as follows:

Answer record table exam_record:

submit_time is the completion time

Filed	Type	Null	Key	Extra	Default	Comment
id	int(11)	NO	AT	auto_increment	(NULL)	auto-increment ID
uid	int(11)	NO			(NULL)	User ID
exam_id	int(11)	NO			(NULL)	paper ID
start_time	datetime	NO			(NULL)	Starting time
submit_time	datetime	YES			(NULL)	submission time
score	tinyint(4)	YES			(NULL)	Score

update exam_record
set score = 0,submit_time = '2099-01-01 00:00:00'
where start_time < '2021-09-01 00:00:00' and score is null;

Please change all unfinished records in the exam_record table that started answering before September 1, 2021 to passive completion, that is, change the completion time to '2099-01-01 00:00:00' and the score to 0.