Shulou(Shulou.com)06/01 Report--

After starting the service with the package, the relevant configuration files will be automatically generated.

The root initial secret is automatically generated the first time it is run

The initial password looks for grep-I password / var/log/mysql.log in the service log file

Get in there, mysql.

Mysql-hlocalhost-uroot-p initial password

Set global validate_password_policy=0

# change password default level is 0

# 0 is the length, 1 is the letter length symbol, 2 is the letter length symbol, dictionary file

Set global validate_password_length=6

# the default length of the modified password is 6

Alter user root@ "localhost" identified by '123456'

# change password

The command line instruction is temporarily valid, and the command is written to the configuration file / etc/my.cnf for permanent effect

Restart the service after the write is completed.

#

Noun interpretation

DB,DataBase

A collection of data organized according to a data model and stored in storage

DBMS,DataBase Management System

Database management system, large server software used to operate and manage databases

DBS, DataBase System

Server with database, database management system

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Classification of sql commands

DDL data definition language

(create alter drop)

DML data manipulation language

(insert update delete)

DCL data control language

(grant revoke)

DTL data transaction language

(commit rollback savepoint)

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2 create a library

Create database library name

# create a library

Show databases

# View existing libraries

Drop database library name

# deleting a library

Select database ()

# View the current library

Use library name

# enter the library

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Build a table

Create table library name. Table name (

Field name type (width) constraint

Field name type (width) constraint

...

...

);

Create table gamedb.stu (

Name char (10), # characters (10)

Age int # numeric value

);

Insert into library name. Table name values (values list)

# insert table record

Select * from library name. Table name

# View table records

Delete from library name. Table name

# Delete table records

Desc library name. Table name

# View table structure

Drop table library name. Table name

# Delete table

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Mysql data type

Numerical type: × ×, floating point type

Integer: according to the range of stored values, the type of integer is divided into:

Type tinyint smallintmediumintintbigint

The use is small, medium and large.

Size 1 byte 2 bytes 3 bytes 4 bytes 8 bytes

Divided into signed and unsigned, the ranges are as follows:

Signed-128-27-32768-2767-2 ^ 23 ~ 2 ^ 23-1-2 ^ 31 ~ 2 ^ 31-1-2 ^ 63 ~ 2 ^ 63-1

Unsigned 02550065535502 ^ 24-10-2 ^ 32-10-2 ^ 64-1

When you use unsigned modification when creating, only positive numbers are saved in the corresponding fields.

The width is only the display width, and the size of the stored value is determined by the type

When using zerofill, fill in 0 instead of blanks

# for example: age int (3)

The insert in to a values (3) database is displayed as 003

An error is reported when the value is out of range

Floating point type: according to the range of storage, it can be divided into single precision and double precision:

Single precision float (nQuery m) 4 bytes

Double precision double (nQuery m) 8 bytes

# n represents the total number of places and m represents the number of decimal places

# for example: float (5) the maximum is 999.99 and the minimum is-999.99

The width of the numeric type is that the display width cannot limit the size of the assignment to the field, which is determined by the field type.

#

Character type:

Fixed length: char (number of characters)

# the maximum length is 255 characters, which is filled with a space on the right if it is not enough to specify the number of characters. If the number of characters exceeds, the data cannot be written.

Variable length: varchar

# allocate storage space according to the actual size of the data. When the number of characters exceeds, the data cannot be written.

Large text type: text/blob

Used when the number of characters is greater than 65535.

Char is used more often in the actual production environment because varchar takes up part of the CPU resources to calculate the storage size.

Date and time type

Year YYYY 2017

# year defaults to 4 as a number. When only 2 digits are used to assign values, 01 to 69 is regarded as 2000 to 2069.

70: 99 is 1970: 1999.

Date date YYYYMMDD20171220

Time time HHMMSS155145

Date and time

Datetime YYYYMMDDHHMMSS

Timestamp YYYYMMDDHHMMSS

When datetime does not assign a value to him, it will be empty

When timestamp does not assign a value to him, it uses the current system time

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Now ()

# time of the current system

Year ()

# get the year in the data

Day ()

# get the days in the data

Date ()

# get the date in the data

Time ()

# get the time in the data

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Enumeration type: the value of a field can only be selected within the range of enumerations

Field name enum (values list)

# Select to select a single value from a given set of values.

Field name set (values list)

# multiple selections, select one or more values from a given set of values.

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Set the constraints of the field: the function limit how to assign a value to the field.

Whether Null is allowed to be empty or not is followed by NOT Null after the type.

Default sets the default value, which defaults to NULL followed by default

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Modify table structure

Mysql > alter table table name execute action

Add field name type (width) constraint

# add a new field. Default is at the end.

Add field name type (width) constraint first

# the front of all fields

Add field name type (width) constraint after field name

# what field should be added after

Drop field name

# deleting a field

Modify field type (width) constraint

# modify field type

Change original field name new field name type (width) constraint

# modify field name

Alter table original table name rename new table name

# modify the table name

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