Python SQLite - 从表中选择数据

在本文中，我们将讨论Python SQLite 模块的 select 语句。此语句用于从 SQLite 表中检索数据，并返回表中包含的数据。

在 SQLite 中，Select 语句的语法是：

SELECT * FROM table_name;

*  : means all the column from the table

To select specific column replace * with the column name or column names.

现在我们将在Python程序中使用 Select 语句并查看结果：

演示我们的 GEEK 表：

创建上表：

在这里，我们将使用上述方法创建表。

Python3

import sqlite3
  
# Connecting to sqlite
# connection object
connection_obj = sqlite3.connect('geek.db')
  
# cursor object
cursor_obj = connection_obj.cursor()
  
connection_obj.execute("""CREATE TABLE GEEK(
  Email varchar(255),
  Name varchar(50),
  Score int
  );""")
  
connection_obj.execute(
    """INSERT INTO GEEK (Email,Name,Score) VALUES ("[e-mail]","Geek1",25)""")
connection_obj.execute(
    """INSERT INTO GEEK (Email,Name,Score) VALUES ("[e-mail]","Geek2",15)""")
connection_obj.execute(
    """INSERT INTO GEEK (Email,Name,Score) VALUES ("[e-mail]","Geek3",36)""")
connection_obj.execute(
    """INSERT INTO GEEK (Email,Name,Score) VALUES ("[e-mail]","Geek4",27)""")
connection_obj.execute(
    """INSERT INTO GEEK (Email,Name,Score) VALUES ("[e-mail]","Geek5",40)""")
connection_obj.execute(
    """INSERT INTO GEEK (Email,Name,Score) VALUES ("[e-mail]","Geek6",36)""")
connection_obj.execute(
    """INSERT INTO GEEK (Email,Name,Score) VALUES ("[e-mail]","Geek7",27)""")
  
connection_obj.commit()
  
# Close the connection
connection_obj.close()

读取所有行：

现在我们将使用 Select 语句从表中检索数据并获取所有记录。要获取所有记录，我们将使用 fetchall() 方法。

Syntax: cursor.fetchall()

where, cursor is an object of sqlite3 connection with database.

代码：

蟒蛇3

import sqlite3
  
# Connecting to sqlite
# connection object
connection_obj = sqlite3.connect('geek.db')
  
# cursor object
cursor_obj = connection_obj.cursor()
  
# to select all column we will use
statement = '''SELECT * FROM GEEK'''
  
cursor_obj.execute(statement)
  
print("All the data")
output = cursor_obj.fetchall()
for row in output:
  print(row)
  
connection_obj.commit()
  
# Close the connection
connection_obj.close()

输出：

阅读一些行：

现在我们将使用 Select 语句从表中检索数据并获取许多记录，而不是全部。要获取许多记录，我们将使用 fetchmany() 方法。

Syntax: cursor.fetchmany(size)

Parameters: size – a limit to fetch records

where, cursor is an object of sqlite3 connection with database.

代码：

蟒蛇3

import sqlite3
  
# Connecting to sqlite
# connection object
connection_obj = sqlite3.connect('geek.db')
  
# cursor object
cursor_obj = connection_obj.cursor()
  
# to select all column we will use
statement = '''SELECT * FROM GEEK'''
  
cursor_obj.execute(statement)
  
print("Limited data")
output = cursor_obj.fetchmany(5)
for row in output:
  print(row)
  
connection_obj.commit()
  
# Close the connection
connection_obj.close()

输出：

只读一行：

现在 e 将使用 Select 语句从表中检索数据并仅获取一条记录。要仅获取一条记录，我们将使用 fetchone() 方法。

Syntax: cursor.fetchone()

where, cursor is an object of sqlite3 connection with database.

蟒蛇3

import sqlite3
  
# Connecting to sqlite
# connection object
connection_obj = sqlite3.connect('geek.db')
  
# cursor object
cursor_obj = connection_obj.cursor()
  
# to select all column we will use
statement = '''SELECT * FROM GEEK'''
  
cursor_obj.execute(statement)
  
print("Only one data")
output = cursor_obj.fetchone()
print(output)
  
connection_obj.commit()
  
# Close the connection
connection_obj.close()

输出：