Mysql basis Two Notes

Excerpt from rookie tutorial, part of the knowledge point record according to my own situation. In order to consolidate a knowledge learned, and secondly for future review.

Create a database

Create command to create a database using the following syntax:

CREATE DATABASE 数据库名;

Delete Database

Use the drop command to delete the database, the syntax is as follows:

Drop database 数据库名；

Mysql Data Types

Mysql data types include numeric, date / time and a character string (character) type.

Numeric types

1. Strict numeric data types: INTGER, SMALLINT, DEDECIMAL and NUMERIC
2. Approximate numeric data types: FLOAT, REAL and DOUBLE PRECISION

Date and Time Types

Including DATETIME, DATE, TIMESTAMP, TIME, and YEAR.
Each type has a value of time effective range and a "zero" value of "zero" when the value of the specified unlawful MySQL can not be represented.

Types of	format
DATE	YYYY-MM-DD
TIME	HH-MM-SS
YEAR	YYYY
DATETIME	YYYY-MM-DD HH-MM-SS
TIMESTAMP	YYYYMMDD HHMMSS

String type

Including CHAR, VARCHAR, BINARY, VARBINARY, BLOB, TEXT, ENUM and SET.

Character length encoding related:
UTF-. 8: characters. 1 = 3 bytes
GBK: 1 = 2 bytes characters

char, varchar, text differences:

1. char: fixed length, length in the range of 0-255 bytes, less than the length of the content 255, storage space filled.
2. varchar: variable length, byte length in the range 0-65535.
3. text: a length in the range of 0-65535 bytes, not have a default value.

tips：

• Varchar field changes often with
• Known and fixed length of 255 length of char
• Try to use varchar
• With a length of more than 255, or text varchar
• Can not text varchar

Create a data table

Syntax:
the Create the Table table name (field name field type);

Null "difference" and a NULL:

1. Null does not occupy space
2. NULL occupy a space
   of any number of operations with NULL is NULL;
   determine whether equal to NULL, = not available, use a keyword is NULL.

Insert data

Syntax:
INSERT INTO table name (field 1, field 2, field ... n) value (value 1, value 2, ... value n)

Query data

Syntax:
SELECT 1 field names, field names 2 from table [where condition]

Query All fields: "*" indicates all the fields
select * from table [where comdition]

update data

Syntax:
Update table set field value 1 = 1, the value of field 2 = 2, ..., n = the value of field 2 [where condition]

A partial data field of the replacement data:
Update table set field a = replace (a field, the character string is replaced, the new string)

delete data

Syntax:
delect from table [where condition];
if no where clause to delete all records in the table.

tips: delete delete only the table data, drop the table structure and data are deleted.

delete, drop, truncate difference:

1. delete and delete only data truncate table data, drop along with the table data and table structure be deleted.
2. delete is DML statements can be rolled back after the completion of soap rub. truncate and drop a DDL statement, the operation takes effect immediately and can not be rolled back.
3. Execution speed: drop-> truncate-> delete