The content of this article refers to the book "SQL Basic Tutorial". For beginners, please give me some advice.
1. Creation of database
1. Create database statements
CREATE DATABASE <Database name>;
2. Example
CREATE DATABAST shop；
2. Creation of table
Before creating a table, you must first create the database in which the table will be stored.
1. Statement to create table
Statement to create table:CREATE TABLE <Table name>
2. Example
The first column is shop, the second column: is the column name of the created table, the third column: data type, for example, CHAR(4) means that the longest string is 4, the fourth column: NOT NULL means the information of this column It cannot be empty, which is a constraint.
3. Specification of data type
(1) CHAR type
Character type, fixed-length string. You can specify the length (maximum length) of the string that the column can store in parentheses like CHAR(10) or CHAR(200).
(2) INTEGER type
Number type, stores integers, cannot store decimals.
(3) VARCHAR type
String type, variable length string. You can also specify the length (maximum length) of the string through the number in brackets.
(4) DATE type
Date type, stores dates.
3. Deletion of table
1. Statement to delete table
DROP TABLE <表名>;
2. Example
If you want to delete the Product table, enter the following statement, but once the table is deleted, it cannot be restored.
DROP TABLE Product;
4. Table update
1. Statement to add columns
ALTER TABLE <表名> ADD COLUMN <列的定义>；
2. Example
ALTER TABLE Product ADD COLUMN product_name_pinyin VARCHAR(100);
Among them, Produce is the table name, product_name_pinyin is the newly added column, and product_name_pinyin is the data type of the newly added column.
3. Statement to delete columns
ALTER TABLE <表名> DROP COLUMN <列的定义>；
4. Example
ALTER TABLE Product DROP COLUMN product_name_pinyin;
5. SQL statements to insert data into the Product table
The BEGIN TRANSACTION statement is the instruction statement to start inserting rows, and the COMMIT statement at the end is the instruction statement to determine the inserted rows.
6. Change table name
ALTER TABLE <Original table name> RENAME TO <New table name>;
7. After-class exercises
1. Create table
2. Update table
Enter \d to view the created tables. Two tables have been created.
3. Delete table
