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📜  Python PostgreSQL-更新表

📅  最后修改于: 2020-11-07 07:55:28             🧑  作者: Mango

您可以使用UPDATE语句修改PostgreSQL中表的现有记录的内容。要更新特定的行，您需要与其一起使用WHERE子句。

句法

以下是PostgreSQL中UPDATE语句的语法-

UPDATE table_name
SET column1 = value1, column2 = value2...., columnN = valueN
WHERE [condition];

例

假设我们使用以下查询创建了一个名为CRICKETERS的表-

postgres=# CREATE TABLE CRICKETERS ( 
   First_Name VARCHAR(255), Last_Name VARCHAR(255), Age int, 
   Place_Of_Birth VARCHAR(255), Country VARCHAR(255)
);
CREATE TABLE
postgres=#

如果我们使用INSERT语句将5条记录插入其中-

postgres=# insert into CRICKETERS values('Shikhar', 'Dhawan', 33, 'Delhi', 'India');
INSERT 0 1
postgres=# insert into CRICKETERS values('Jonathan', 'Trott', 38, 'CapeTown', 'SouthAfrica');
INSERT 0 1
postgres=# insert into CRICKETERS values('Kumara', 'Sangakkara', 41, 'Matale', 'Srilanka');
INSERT 0 1
postgres=# insert into CRICKETERS values('Virat', 'Kohli', 30, 'Delhi', 'India');
INSERT 0 1
postgres=# insert into CRICKETERS values('Rohit', 'Sharma', 32, 'Nagpur', 'India');
INSERT 0 1

以下声明修改了板球运动员的年龄，该板球运动员的名字为Shikhar-

postgres=# UPDATE CRICKETERS SET AGE = 45 WHERE FIRST_NAME = 'Shikhar' ;
UPDATE 1
postgres=#

如果您检索FIRST_NAME是Shikhar的记录，则会观察到年龄值已更改为45-

postgres=# SELECT * FROM CRICKETERS WHERE FIRST_NAME = 'Shikhar';
 first_name | last_name | age | place_of_birth | country
------------+-----------+-----+----------------+---------
Shikhar     | Dhawan    | 45  | Delhi          | India
(1 row)

postgres=#

如果您未使用WHERE子句，则所有记录的值都将更新。以下UPDATE语句使CRICKETERS表中的所有记录的寿命增加1-

postgres=# UPDATE CRICKETERS SET AGE = AGE+1;
UPDATE 5

如果使用SELECT命令检索表的内容，则可以看到更新后的值为-

postgres=# SELECT * FROM CRICKETERS;
 first_name | last_name  | age | place_of_birth | country
------------+------------+-----+----------------+-------------
Jonathan    | Trott      | 39  | CapeTown       | SouthAfrica
Kumara      | Sangakkara | 42  | Matale         | Srilanka
Virat       | Kohli      | 31  | Delhi          | India
Rohit       | Sharma     | 33  | Nagpur         | India
Shikhar     | Dhawan     | 46  | Delhi          | India
(5 rows)

使用Python更新记录

psycopg2的游标类提供了一个名为execute()方法的方法。此方法接受查询作为参数并执行它。

因此，要使用Python将数据插入PostgreSQL中的表中-

  • 导入psycopg2软件包。

  • 通过将用户名，密码，主机(可选的默认值：localhost)和数据库(可选)作为参数传递给connect()方法，创建连接对象。

  • 通过将false设置为属性autocommit的值来关闭自动提交模式。

  • psycopg2库的Connection类的cursor()方法返回一个游标对象。使用此方法创建一个游标对象。

  • 然后，通过将UPDATE语句作为参数传递给execute()方法来执行该语句。

例

以下Python代码更新Employee表的内容并检索结果-

import psycopg2
#establishing the connection
conn = psycopg2.connect (
   database="mydb", user='postgres', password='password', host='127.0.0.1', port= '5432'
)

#Setting auto commit false
conn.autocommit = True

#Creating a cursor object using the cursor() method
cursor = conn.cursor()

#Fetching all the rows before the update
print("Contents of the Employee table: ")
sql = '''SELECT * from EMPLOYEE'''
cursor.execute(sql)
print(cursor.fetchall())

#Updating the records
sql = "UPDATE EMPLOYEE SET AGE = AGE + 1 WHERE SEX = 'M'"
cursor.execute(sql)
print("Table updated...... ")

#Fetching all the rows after the update
print("Contents of the Employee table after the update operation: ")
sql = '''SELECT * from EMPLOYEE'''
cursor.execute(sql)
print(cursor.fetchall())

#Commit your changes in the database
conn.commit()

#Closing the connection
conn.close()

输出

Contents of the Employee table:
[
   ('Ramya', 'Rama priya', 27, 'F', 9000.0), 
   ('Vinay', 'Battacharya', 20, 'M', 6000.0), 
   ('Sharukh', 'Sheik', 25, 'M', 8300.0), 
   ('Sarmista', 'Sharma', 26, 'F', 10000.0), 
   ('Tripthi', 'Mishra', 24, 'F', 6000.0)
]
Table updated......
Contents of the Employee table after the update operation:
[
   ('Ramya', 'Rama priya', 27, 'F', 9000.0), 
   ('Sarmista', 'Sharma', 26, 'F', 10000.0), 
   ('Tripthi', 'Mishra', 24, 'F', 6000.0), 
   ('Vinay', 'Battacharya', 21, 'M', 6000.0), 
   ('Sharukh', 'Sheik', 26, 'M', 8300.0)
]