Python PostgreSQL – Where 子句

在本文中，我们将看到如何使用Python的Psycopg2 在 PostgreSQL 中使用 Where 子句。

Where 子句帮助我们轻松处理数据库。正如我们所知，我们的数据库中存储了大量数据，因此仅提取有用和必需的信息子句是有帮助的。 WHERE子句用于仅提取满足所需条件的记录。

Syntax: SELECT column1, column2, ….. FROM table_name WHERE condition

使用 where 子句的表格演示：

示例：首先，这里我们展示了如何创建一个表，然后在其中插入值。

Python3

import psycopg2
 
# establishing the connection
conn = psycopg2.connect(
    database="test",
    user='postgres',
    password='password',
    host='localhost',
    port='5432'
)
 
# Creating a cursor object using the cursor() method
cursor = conn.cursor()
 
sql = '''CREATE TABLE WORKER(
   ID BIGSERIAL NOT NULL PRIMARY KEY,
   NAME VARCHAR(100) NOT NULL,
   COUNTRY VARCHAR(50) NOT NULL,
   AGE INT,
   SALARY FLOAT   
)'''
cursor.execute(sql)
 
# Inserting values into the table
insert_stmt = "INSERT INTO WORKER (NAME, COUNTRY, AGE, SALARY) \
VALUES (%s, %s, %s, %s)"
data = [('Krishna', 'India', 19, 2000),
        ('Harry', 'USA', 20, 7000),
        ('Malang', 'Nepal', 25, 5000),
        ('Apple', 'London', 26, 2000),
        ('Vishnu', 'India', 29, 2000),
        ('Frank', 'UAE', 21, 7000),
        ('Master', 'USA', 25, 5000),
        ('Montu', 'India', 26, 2000),
        ]
cursor.executemany(insert_stmt, data)
 
# Retrieving specific records using the where clause
cursor.execute("SELECT * from WORKER WHERE AGE <23")
print(cursor.fetchall())
 
# Retrieving specific records using the where clause
cursor.execute("SELECT * from WORKER WHERE COUNTRY='India' ")
print(cursor.fetchall())
 
 
# Retrieving name of employees whose salary is 5000
cursor.execute("SELECT name from WORKER WHERE salary=5000 ")
print(cursor.fetchall())
 
# Retrieving name and country of employees whose salary is 2000
cursor.execute("SELECT name, country from WORKER WHERE salary=2000 ")
print(cursor.fetchall())
 
# Commit your changes in the database
conn.commit()
 
# Closing the connection
conn.close()

输出：

在Python使用 pyscopg2 的 where 子句