一、SQLite的基础
SQLite是一个轻型的嵌入式关系型数据库管理系统,它的数据存储在单一的磁盘文件中。它可以使用SQL语言进行操作,支持大部分SQL语法,包括事务、触发器、索引等。SQLite不像传统的数据库那样需要安装、启动和配置,只需要将SQLite的可执行文件和开发库文件导入到项目中即可。
SQLite的代码示例:
import sqlite3 conn = sqlite3.connect('test.db') print("Opened database successfully") conn.execute('''CREATE TABLE COMPANY (ID INT PRIMARY KEY NOT NULL, NAME TEXT NOT NULL, AGE INT NOT NULL, ADDRESS CHAR(50), SALARY REAL);''') print("Table created successfully") conn.close()
二、SQLite的数据类型
SQLite支持多种数据类型,包括NULL、INTEGER、REAL、TEXT以及BLOB等数据类型。在创建表的时候需要为每一个字段指定数据类型,一旦指定无法更改。SQLite的数据类型并不需要指定长度,因为SQLite会根据实际存储的数据自动调整字段的长度。例如,如果字段类型为TEXT,那么SQLite会自动根据存储的内容分配相应的长度。
SQLite的数据类型示例:
import sqlite3 conn = sqlite3.connect('test.db') print ("Opened database successfully") conn.execute('''CREATE TABLE COMPANY (ID INT PRIMARY KEY NOT NULL, NAME TEXT NOT NULL, AGE INT NOT NULL, ADDRESS CHAR(50), SALARY REAL);''') print ("Table created successfully") conn.close()
三、SQLite的事务
SQLite支持ACID事务,也就是Atomicity(原子性)、Consistency(一致性)、Isolation(隔离性)和Durability(持久化)。如果在事务中的任意一步骤出现错误,那么整个事务会被回滚,使得数据库的状态恢复到操作之前的状态。
SQLite的事务代码示例:
import sqlite3 conn = sqlite3.connect('test.db') print ("Opened database successfully") conn.execute('''CREATE TABLE COMPANY (ID INT PRIMARY KEY NOT NULL, NAME TEXT NOT NULL, AGE INT NOT NULL, ADDRESS CHAR(50), SALARY REAL);''') print ("Table created successfully") conn.execute("INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) \ VALUES (1, 'Paul', 32, 'California', 20000.00 )") conn.execute("INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) \ VALUES (2, 'Allen', 25, 'Texas', 15000.00 )") conn.execute("INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) \ VALUES (3, 'Teddy', 23, 'Norway', 20000.00 )") conn.execute("INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) \ VALUES (4, 'Mark', 25, 'Rich-Mond', 65000.00 )") conn.commit() print ("Records created successfully") conn.close()
四、SQLite的索引
索引是一种特殊的数据结构,用于加速查询操作。SQLite支持B-Tree和Hash索引,可以使用CREATE INDEX语句创建索引。可以根据需要为一个表创建多个索引,每一个索引可以包含多列,可以根据索引的列进行排序和过滤。
SQLite的索引代码示例:
import sqlite3 conn = sqlite3.connect('test.db') print ("Opened database successfully") conn.execute('''CREATE TABLE COMPANY (ID INT PRIMARY KEY NOT NULL, NAME TEXT NOT NULL, AGE INT NOT NULL, ADDRESS CHAR(50), SALARY REAL);''') print ("Table created successfully") conn.execute("CREATE INDEX IDX_NAME ON COMPANY (NAME)") conn.execute("INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) \ VALUES (1, 'Paul', 32, 'California', 20000.00 )") conn.execute("INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) \ VALUES (2, 'Allen', 25, 'Texas', 15000.00 )") conn.execute("INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) \ VALUES (3, 'Teddy', 23, 'Norway', 20000.00 )") conn.execute("INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) \ VALUES (4, 'Mark', 25, 'Rich-Mond', 65000.00 )") conn.commit() print ("Records created successfully") conn.close()
五、SQLite的触发器
SQLite的触发器是一种特殊的数据库对象,它可以捕获特定的数据库事件(如INSERT、UPDATE、DELETE等),并在事件发生时自动执行某些操作。通过使用触发器,可以方便地保持数据库的完整性和约束。
SQLite的触发器代码示例:
import sqlite3 conn = sqlite3.connect('test.db') print ("Opened database successfully") conn.execute('''CREATE TABLE COMPANY (ID INT PRIMARY KEY NOT NULL, NAME TEXT NOT NULL, AGE INT NOT NULL, ADDRESS CHAR(50), SALARY REAL);''') print ("Table created successfully") conn.execute('''CREATE TRIGGER salary_update AFTER UPDATE ON COMPANY FOR EACH ROW WHEN NEW.SALARY > 50000 BEGIN INSERT INTO HIGH_SALARY (ID, NAME, AGE, SALARY) VALUES (NEW.ID, NEW.NAME, NEW.AGE, NEW.SALARY); END;''') conn.execute("INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) \ VALUES (1, 'Paul', 32, 'California', 20000.00 )") conn.execute("INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) \ VALUES (2, 'Allen', 25, 'Texas', 15000.00 )") conn.execute("INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) \ VALUES (3, 'Teddy', 23, 'Norway', 20000.00 )") conn.execute("INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) \ VALUES (4, 'Mark', 25, 'Rich-Mond', 65000.00 )") conn.commit() print ("Records created successfully") conn.close()
结束语
本文详细地阐述了SQLite数据库的多个方面,包括基础、数据类型、事务、索引以及触发器等方面,并给出了对应的代码示例。SQLite有着小巧、便捷和易用等优点,广泛应用于跨平台开发中,值得开发者们深入了解。