MYSQL learning notes - basic use of database

Keywords: Database MySQL Big Data

1, mysql database common operations

Account login

-h specifies the host address of the server, - p specifies the port number, - u specifies the current shell user, - p is the password, which can not be entered on the command line

Create database

The database is a collection of tables. The database server can contain multiple databases. The logical relationship is as follows:
Database server - > Database - > Table - > row.

Create a database named company

1. About sql statements: case insensitive under windows, case sensitive under linux, default to\ G. \ g end.
2. When the database name contains special characters such as period (.), the anti marking character ` ` needs to be used.

View current data directory

mysql> show variables like 'datadir';

View databases that you have access to

mysql> show databases;

mysql data type

integerRangeByte size
BITUnsigned [0255], signed [- 128127]1
TINYINTInteger [0255]1
SMALLINTUnsigned [065535], signed [- 3276832767]2
MEDIUMINTUnsigned [0224-1], signed [- 223,2 ^ 23-1]]3
INTUnsigned [0232-1], signed [- 231,2 ^ 31-1]4
BIGINTUnsigned [0264-1], signed [- 263, 2 ^ 63 - 1]8

Note: one byte is 8-bit binary

floating-pointRangeByte size
DECIMAL(M,D)It is determined by M (the length of the whole number, including the decimal point, the number of digits to the left of the decimal point, the number of digits to the right of the decimal point, but excluding the minus sign) and D (the number of digits to the right of the decimal point). M defaults to 10 and D defaults to 0
FLOAT(-3.402823466E+38 ,-1.175494351E-38),0,(1.175494351E-38 - 3.402823466E+38)4
DOUBLE(-1.7976931348623157E+308 - -2.2250738585072014E-308),0,(2.2250738585072014E-308 - 1.7976931348623157E+308)8

Note: one byte is 8-bit binary

character stringdefinitionByte size
CHARFixed length string0-255 bytes
VARCHARVariable length string0-65535 bytes
TEXTLong text data0-65 535 bytes

BINARY and VARBINARY are similar to CHAR and VARCHAR, except that they contain BINARY strings instead of non BINARY strings. That is, they contain byte strings instead of character strings. This means that they have no character set, and they sort and compare numeric values based on column value bytes.

In addition, it also includes JSON, time and other data types.

2, Table operation

Create table

mysql> CREATE TABLE IF NOT EXISTS `CUSTOMERS` (`id` int unsigned
     -> `first_name` varchar(20),
     -> `last_name` varchar(20),
     -> `country` varchar(20)
     -> ) ENGINE=InnoDB;

The content is explained as follows:

  1. ``The meaning is shown above.
  2. IF NOT EXISTS, do not create if it exists, and warn if it exists.
  3. AUTO_INCREMENT means that the key increases automatically; PRIMARY KEY stands for PRIMARY KEY.
  4. InnoDB is the storage engine and the default engine. In addition, MYISAM is commonly used.
  5. There is no punctuation in the last place of the table definition. country varchar(20)

View table structure

mysql> SHOW CREATE TABLE customers\G
*************************** 1. row ***************************
       Table: customers
Create Table: CREATE TABLE `customers` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `first_name` varchar(20) DEFAULT NULL,
  `last_name` varchar(20) DEFAULT NULL,
  `country` varchar(20) DEFAULT NULL,
  PRIMARY KEY (`id`)
1 row in set (0.00 sec)

Explanation: \ the function of G is to turn the detected structure 90 degrees into vertical


mysql> DESC customers;

Clone a new table

mysql> CREATE TABLE new_customers LIKE customers;

3, Add, delete, modify and query

insert data

INSERT IGNORE INTO Table name (field) VALUES(value) 

Note: if the declared unique field is repeated, the IGNORE statement will be executed and the new data will be ignored, but the id will still increase by 1.

INSERT INTO Table name (field) VALUES(value) ON DUPLICATE KEY (operation)

Note: if you want to trigger some operations when a unique field is encountered, use ON DUPLICATE KEY

update fields

UPDATE Table name SET (field)=(value) WHERE (condition)

Delete field

DELETE FROM Table name  WHERE (condition)

Delete table



IN operation: check whether a value is IN a group of values.

mysql> select * from Table name where field IN (Candidate value 1,Candidate value 2,......,Candidate value n);

BETWEEN... AND: select according to the range

mysql>select * from customer where field between Left interval and Right interval;

Note: both the left section and the right section can be obtained.

NOT: negate the condition and select the item that does NOT meet the condition.

Field matching

Simple matching

The underscore () matches exactly one character, the percent sign (%) matches greedily, and matches as many characters as possible.

#Match all names with M
mysql> select * from customer where first_name like '%M%';

#Match all names with the first three letters of MAR and the name length of 4
mysql> select * from customer where first_name like 'MAR_';

Regular matching

# Writing method 1 
mysql> select * from Table name where field rlike 'regular expression ';

# Writing method 2
mysql> select * from Table name where field  regexp 'regular expression ';

For common usage, see regular expression syntax
Note. * represents greedy matching. *? Represents the minimum match

Posted by AjithTV on Tue, 14 Sep 2021 15:23:04 -0700