mysql database syntax and CRUD

table of Contents

First, the basic operation of the database

Second, the type of database column

Third, database type

Fourth, the operating table

Five, CRUD

First, the basic operation of the database

1 View all databases

show databases;

2, into the database

use database name;

3, delete the database

drop database [IF EXISTS (absence not being given, warning)] database name;

4, see the table (the premise: access to the database)

describe [IF NOT EXISTS (absence not being given, warning)] table;

5. Create a database

create database [if not exists] database name;

Second, the type of database column

1, the value

• int 4 bytes of data storage criteria

• large data storage bigint 8 bytes

• a string of decimal floating-point numbers (financial calculation, data-sensitive industries)

• tinyint very small data one byte

• smallint 2 bytes smaller data

• mediumint medium-sized data of the three bytes

• Float float 4 bytes

• double floating point number 8 bytes

2, string

• The variable string varchar 0 ~ 65535 String (Java)
• text text string 2 ^ 16-1 save large files
• char string of fixed size of 0 to 255
• micro text tinytext 2 ^ 8-1

3, the date and time

• datetime YYY-MM-DD HH: mm: ss format most commonly used time
• 1970.1.1 timestamp to the current time stamp milliseconds
• data YYY-MM-DD, date format
• time HH: mm: ss, time format
• year year

4、null

• Does not make sense, generally do not hook is not empty, the default is usually null

Third, database type

1、MYISAM和INNODB

	MYISAM	INNODB
Affairs	not support	stand by
Datarows	not support	stand by
Foreign key constraint	not support	stand by
Full-text index	stand by	not support
Table space size	Small	About 2 times MYISAM
the difference	Space saving, fast	High security, support for transaction processing, multi-table multi-user operation

Fourth, the operating table

1, modify the table name

Old alter table table name rename as a new table name

2, increasing the fields of the table

alter table fields add ranked attribute table []

3, modify the constraints

alter table modify field ranked attribute table []

4, field rename

alter table table name change old field names among the new field attributes []

5, with the constraint modifying fields rename

Modify the constraints	Rename the field
The column properties modify the field names of fields, such as the int to varchar, modify a table constraint (constraint modification only)	Change the name field, must take the column properties can also be modified constraint (you can modify the name and constraints)

6, delete table fields

alter table table name drop field names

7, delete the table

drop table [if exists] 表名

8, the foreign key (cool)

In the application layer is now generally used to write the code

alter table表名 add constraint fk_外键字段 foreign key(外键字段) references 外链表(外键字段)

You must first remove the sheet list can link

Five, CRUD

1, increasing the data (field value must correspond) (the DML Language)

Single-line increase: to increase the one-way data

Syntax: insert into table (field 1, field 2, field 3, ...) values ​​( 'value 1', 'value 2', 'value 3', ...);

Example: insert into people (id, name, gender) values ​​( '1', 'John Doe', 'M 1');

A plurality of rows increases: a plurality of rows increases even two rows of data (with the first and second rows, spaced apart from, the other and so on)

Syntax: insert into table (field 1, field 2, field 3, ...) values ​​( 'value 1', 'value 2', 'value 3'), ( 'value 1', 'value 2', 'values ​​3 ');

Example: insert into people (id, name, gender) values ​​( '1', 'John Doe', '1'), ( '2', 'John Doe', 1 ');

2, modify data (a plurality of data modification, separated) (the DML Language)

Format: update table name = name of the new column set value [name = new value column] WHERE column name = value [and column name = value];

• Later data set is required to modify the column (a plurality of modified data separated by commas).
• It is a condition where the back (with a plurality of conditions are met and, with only a need to meet or), for locking the need to modify the line (conditional operators may be used).

Operation operator:

Operators	meaning	Examples	result
=	equal	1=2	false
<> Or! =	not equal to	1!=2	true
>	more than the	1>2	false
<	Less than	1<2	true
<=	less than or equal to	1<=2	true
>=	greater than or equal to	1>=2	false
between … and …	Within a certain range	id between 1 and 2;	id in [2] are met within
and	&& and must both meet	id = 1 && username = 'John Doe'	Both to meet the return true
or	|| or only need to meet a	id = 2 || username = 'John Doe'	As long as a satisfying return true

★ Be sure to add conditions, otherwise all the data that column all the changes, if there are one million, one million will change.

例：update student_user set age = 18 where id = 3；

例：update student_user set age = 18 where id = 3 and username = '‘小琦’;

Wrong Demonstration:

3, delete data (DML language)

1.delete

Syntax: delete from table where conditions; (you can not add conditions, but will empty all the data, plus the conditions will delete the specified column)

例：delete from student_user where id = 1;

2.truncate (dedicated to the empty database table structure and the constraint index will not change)

Syntax: truncate table name;

And truncate the difference 3.delete

	delete	truncate
Same point	Data can be deleted without deleting the table structure	Data can be deleted without deleting the table structure
difference	Increment data calculator, not cleared	You can make the increment data counter is cleared, again from the beginning
	It will affect the transaction	It will not affect the transaction

4.delete deleted, restart the database

• INNODB Engine: increment restart from 1 (stored in memory, power outages and lost);
• MYISAM engine: do not start at 1 and continue on a self-increment from the beginning (stored in a file, will not be lost because of power failure);

4, query data (DQL, focus)

DQL (Data Query language): data query language;

• All queries are using select
• Simple and complex queries can all be done
• The most important language database
• Project 90% of the time using query

Single-table query: select * (* indicates that the query all the columns, you can also check the specified column) from table where [condition];

例：select username,passwrod form student_user where id = 3;

Since the column data can give an alias (using as keywords):

Multi-table query: select * (* representing a query for all the columns, the query may specify the column) from Table 1, Table 2 where [Condition];

例：select username,passwrod form student_user,people where id = 3;

Can give table names and column data from an alias (used as keywords):

MySQL the SELECT query: https://blog.csdn.net/sabstarb/article/details/105080290

back to the top