Once you get connected with the MySQL server, it is required to select a database to work with. This is because there might be more than one database available with the MySQL Server.
Selecting MySQL Database from the Command Prompt
It is very simple to select a database from the mysql> prompt. You can use the SQL command use to select a database.
Example
Here is an example to select a database called TUTORIALS −
[root@host]# mysql -u root -p Enter password:****** mysql> use TUTORIALS; Database changed mysql>Now, you have selected the TUTORIALS database and all the subsequent operations will be performed on the TUTORIALS database.
NOTE − All the database names, table names, table fields name are case sensitive. So you would have to use the proper names while giving any SQL command.
Selecting a MySQL Database Using PHP Script
PHP uses mysqli_select_db function to select the database on which queries are to be performed. This function takes two parameters and returns TRUE on success or FALSE on failure.
Syntax
mysqli_select_db ( mysqli $link , string $dbname ) : bool1 | $link Required - A link identifier returned by mysqli_connect() or mysqli_init(). |
2 | $dbname Required - Name of the database to be connected. |
Example
Try the following example to select a database −
Copy and paste the following example as mysql_example.php −
Output
Access the mysql_example.php deployed on apache web server and verify the output.
Database TUTORIALS selected successfullyHandy MySQL Commands
Description
Command
To login (from unix shell) use -h only if needed.
[mysql dir]/bin/mysql -h hostname -u root -p
Create a database on the sql server.
create database [databasename];
List all databases on the sql server.
show databases;
Switch to a database.
use [db name];
To see all the tables in the db.
show tables;
To see database's field formats.
describe [table name];
To delete a db.
drop database [database name];
To delete a table.
drop table [table name];
Show all data in a table.
SELECT * FROM [table name];
Returns the columns and column information pertaining to the designated table.
show columns from [table name];
Show certain selected rows with the value "whatever".
SELECT * FROM [table name] WHERE [field name] = "whatever";
Show all records containing the name "Bob" AND the phone number
'3444444'.
SELECT * FROM [table name] WHERE name = "Bob" AND phone_number = '3444444';
Show all records not containing the name "Bob" AND the phone number '3444444' order by the phone_number field.
SELECT * FROM [table name] WHERE name != "Bob" AND phone_number = '3444444' order by phone_number;
Show all records starting with the letters 'bob' AND the phone number
'3444444'.
SELECT * FROM [table name] WHERE name like "Bob%" AND phone_number = '3444444';
Use a regular expression to find records. Use "REGEXP BINARY" to force case-sensitivity. This finds any record beginning with a.
SELECT * FROM [table name] WHERE rec RLIKE "^a$";
Show unique records.
SELECT DISTINCT [column name] FROM [table name];
Show selected records sorted in an ascending (asc) or descending
(desc).
SELECT [col1],[col2] FROM [table name] ORDER BY [col2] DESC;
Count rows.
SELECT COUNT(*) FROM [table name];
Join tables on common columns.
select lookup.illustrationid, lookup.personid,person.birthday from lookup
left join person on lookup.personid=person.personid=statement to join birthday in person table with primary illustration id;
Switch to the mysql db. Create a new user.
INSERT INTO [table name] (Host,User,Password) VALUES('%','user',PASSWORD('password'));
Change a users password.(from unix shell).
[mysql dir]/bin/mysqladmin -u root -h hostname.blah.org -p password
'new-password'
Change a users password.(from MySQL prompt).
SET PASSWORD FOR 'user'@'hostname' = PASSWORD('passwordhere');
Switch to mysql db.Give user privilages for a db.
INSERT INTO [table name] (Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv,Create_priv,Drop_priv) VALUES ('%','db','user','Y','Y','Y','Y','Y','N');
To update info already in a table.
UPDATE [table name] SET Select_priv = 'Y',Insert_priv = 'Y',Update_priv = 'Y' where [field name] = 'user';
Delete a row(s) from a table.
DELETE from [table name] where [field name] = 'whatever';
Update database permissions/privilages.
FLUSH PRIVILEGES;
Delete a column.
alter table [table name] drop column [column name];
Add a new column to db.
alter table [table name] add column [new column name] varchar (20);
Change column name.
alter table [table name] change [old column name] [new column name] varchar (50);
Make a unique column so you get no dupes.
alter table [table name] add unique ([column name]);
Make a column bigger.
alter table [table name] modify [column name] VARCHAR(3);
Delete unique from table.
alter table [table name] drop index [colmn name];
Load a CSV file into a table.
LOAD DATA INFILE '/tmp/filename.csv' replace INTO TABLE [table name] FIELDS TERMINATED BY ',' LINES TERMINATED BY '\n' (field1,field2,field3);
Dump all databases for backup. Backup file is sql commands to recreate all db's.
[mysql dir]/bin/mysqldump -u root -ppassword --opt >/tmp/alldatabases.sql
Dump one database for backup.
[mysql dir]/bin/mysqldump -u username -ppassword --databases databasename >/tmp/databasename.sql
Dump a table from a database.
[mysql dir]/bin/mysqldump -c -u username -ppassword databasename tablename > /tmp/databasename.tablename.sql
Restore database (or database table) from backup.
[mysql dir]/bin/mysql -u username -ppassword databasename < /tmp/databasename.sql
Create Table Example 1.
CREATE TABLE [table name] (firstname VARCHAR(20), middleinitial VARCHAR(3), lastname VARCHAR(35),suffix VARCHAR(3),
officeid VARCHAR(10),userid VARCHAR(15),username VARCHAR(8),email VARCHAR(35),phone VARCHAR(25), groups
VARCHAR(15),datestamp DATE,timestamp time,pgpemail VARCHAR(255));
Create Table Example 2.
create table [table name] (personid int(50) not null auto_increment primary key,firstname varchar(35),middlename varchar(50),lastname varchar(50) default 'bato');