MySQL exercises "one" additional question

1. Create message database: LIUYANDB;
2. Create a message form Liuyan in the LIUYANDB database, with the following structure:

Table name		Liuyan		Message Information Form
Serial number	Field name	Field description	Type	Property	Note
1	Id	Number	Int (4)	Non-empty	Primary key, self-increment 1
2	Title	Title	varchar (32)	Non-empty
3	Author	Author	varchar (16)	Can be empty
4	Addtime	Message time	Datatime	Non-empty
5	Content	Message content	Text	Non-empty
6	Isdelete	Whether to delete	char (1)	Non-empty	Default value 0

1. Add a column status at the end of the message list (status char (1) default value is 0)
2. Modify the message table author default value is ' Youku ', set to non-empty
3. Remove the Isdelete field from the Liuyan table
4. Add >5 test data to the message table

1. Required to change the value of author field to admin in information with ID value greater than 3
2. Delete the data with ID number 4.

Additional questions:

1. Add >15 test data to the message table, require three users to add
2. Check all message information
3. Query a user's message information.
4. Queries all data, sorted by time in descending order.
5. Get message with ID from 2 to 6 and sort by time descending
6. Count the number of messages left by each user and sort them from small to large.
7. Change the author of two data with ID 8 and 9 to ' Doudou '.
8. Take out the latest three messages. (use limit).
9. Query message contains "D" letter message, and according to the message time from small to large sort
10. Delete "Author" duplicate data and retain one author with the largest ID

MySQL Exercises "One" additional question