Basic MySQL operations

Basic MySQL operations:TestFirst, remember to add the; (semicolon) at the end of each command)
1.Export the entireDatabase
Mysqldump-u username-p -- default-character-set = Latin1 Database Name> exported file name (the default database encoding is Latin1)
Mysqldump-u wcnc-P smgp_rj_wcnc> wcnc. SQL
2.Export a table
Mysqldump-u user name-P database name Table Name> exported file name
Mysqldump-u wcnc-P smgp_rj_wcnc users> wcnc_users. SQL
3.Export a database structure
Mysqldump-u wcnc-p-D-add-drop-Table smgp_apps_wcnc> D: wcnc_db. SQL
-D no data-add-drop-table add a drop table before each create statement
4.Import Database
Common source commands
Go to the MySQL Database Console,
For example, MySQL-u root-P
Mysql> Use Database
Then run the source command. The following parameter is the script file (for example,. SQL used here)
Mysql> source D: wcnc_db. SQL

1. Start and exit
1. Go to MySQL: Start MySQL command line client (MySQL dos Interface) and enter the password for installation. The prompt is: mysql>
2. Exit MYSQL:QuitOrExit
Ii. Database Operations
1. Create a database
Command:Create Database<Database Name>
For example, create a database named xhkdb.
Mysql> Create Database xhkdb;
2. display all databases
Command:Show Databases(Note: There is a last S)
Mysql>Show Databases;
3. delete a database
Command:DROP DATABASE<Database Name>
For example, delete a database named xhkdb.
Mysql>DROP DATABASEXhkdb;
4. Connect to the database
Command:Use<Database Name>
For example, if the xhkdb database exists, try to access it:
Mysql>UseXhkdb;
On-screen prompt: Database changed
5. Database Selected (connected)
Mysql>Select database ();

6. Table information contained in the current database:
Mysql>Show tables; (Note: There is a last S)

Iii. Table operations. A database should be connected before operations
1. Create a table
Command:Create Table<Table Name> (<field name 1> <type 1> [,... <field name n> <type N>]);

Mysql>Create TableMyclass (
> ID int (4) not nullPrimary Key auto_increment,
> Name char (20) not null,
> Sex int (4) not nullDefault'0 ',
> Degree double (16, 2 ));
2. Get the table structure
Command:DescTable name, orShow columns fromTable Name
Mysql>DescribeMyclass
Mysql>DescMyclass;
Mysql>Show columns from myclass;
3. delete a table
Command:Drop table<Table Name>
For example, delete a table named myclass.
Mysql>Drop tableMyclass;
4. insert data
Command:Insert<Table Name> [(<field name 1> [,... <field name n>])]Values(Value 1) [, (value n)]
For example, insert two records into the myclass table. The two records indicate that the result of Tom numbered 1 is 96.45, and the result of Joan numbered 2 is 82.99, wang, numbered 3, scored 96.5.
Mysql>InsertMyclassValues(1, 'Tom ', 96.45), (2, 'job', 82.99), (2, 'wang', 96.59 );
5. query the data in the table
1) query all rows
Command:Select<Field 1, Field 2,...>From<Table Name>Where<Expression>
For example, you can view all data in the myclass table.
Mysql> select * From myclass;
2) query the first few rows of data
For example, view the first two rows of data in the myclass table.
Mysql>Select * fromMyclassOrderIDLimit0, 2;
6. Delete table data
Command:Delete fromTable NameWhereExpression
For example, delete the record numbered 1 in myclass.
Mysql>Delete fromMyclassWhereId = 1;
7. Modify Table data:UpdateTable NameSetField = new value ,...WhereCondition
Mysql>UpdateMyclassSetName = 'Mary'WhereId = 1;
7. Add fields to the table:

Command:ALTER TABLETable NameAddField TypeOthers;
For example, a passtest field is added to the myclass table. The type is int (4) and the default value is 0.
Mysql>ALTER TABLEMyclassAddPasstestInt(4)Default'0'
8. Change the table name:
Command:RENAME TABLEOriginal table nameToNew table name;
For example, the myclass name in the table is changed to youclass.
Mysql>RENAME TABLEMyclassToYouclass;

Update field content
Update table name set field name = new content
Update table name set field name = Replace (field name, 'old content', 'new content ');

Add four spaces before the article
Update article set content = Concat ('', content );

Field Type
1. Int [(m)] type: normal Integer type
2. Double [(m, D)] [zerofill] type: normal size (Double Precision) floating point number type
3. date type: the supported range is 1000-01-01 to 9999-12-31. MySQL displays date values in YYYY-MM-DD format, but allows you to assign values to the date column using strings or numbers
4. Char (m) type: fixed-length string type. When stored, it always fills the Right to the specified length with spaces
5. Blob text type, with a maximum length of 65535 (2 ^ 16-1) characters.
6. varchar: variable-length string type

MySQLHow to define foreign keys

Prerequisites for creating a foreign key: the columns in the table must be of the same type as the foreign key (the foreign key must be the external primary key ).

Foreign key: Associate two tables. A foreign key can only reference the values of columns in the External table!

Specify the primary key Keyword: foreign key (column name)

Reference foreign key Keyword: References <foreign key table name> (foreign key column name)

Event trigger restrictions: On Delete and on update. You can set the parameters cascade, restrict, and set null ), set default (Set default value), [Default] no action

For example:

Outtable table primary key ID type int

Create a table with foreign keys:
Create Table temp (
Id int,
Name char (20 ),
Foreign key (ID) References outtable (ID) on Delete cascade on update cascade );

Note: set the ID column as the foreign key reference External table ID column as the foreign key value Delete this table corresponding to the column sieve when the foreign key value changes the corresponding column value in this table.

5. Import database tables
(1) create a. SQL File
(2) first generate a database such as auction. C: mysqlbin> mysqladmin-u root-P creat auction. A prompt is displayed, indicating that the password is entered and created successfully.
(2) import the auction. SQL File
C: mysqlbin> mysql-u root-P auction <auction. SQL.
With the preceding operations, you can create a database auction and a table auction.
6. Modify the database
(1) Add fields to the MySQL table:
Alter table dbname add column userid int (11) not null primary key auto_increment;
In this way, a field userid is added to the dbname table and the type is int (11 ).
7. MySQL database authorization
Mysql> grant select, insert, delete, create, drop
On *. * (orTest. */User .*/..)
To username @ localhost
Identified by 'Password ';
For example, to create a new user account for database access, perform the following operations:
Mysql> grant usage
-> On test .*
-> Totestuser @ localhost;
Query OK, 0 rows affected (0.15 Sec)
Then a new user named testuser is created. This user can only connect to the database from localhost and connect to the test database. Next, we must specify the operations that the user testuser can perform:
Mysql> grant select, insert, delete, update
-> On test .*
-> Totestuser @ localhost;
Query OK, 0 rows affected (0.00 Sec)
This operation enables testuser to perform select, insert, delete, and update queries on the tables in each test database. Now we end the operation and exit the mysql client program:
Mysql> exit
Bye