postgres数据的增删改查
时间: 2023-12-02 21:06:34 浏览: 30
PostgreSQL是一种关系型数据库管理系统,支持SQL语言,可以通过SQL语句实现数据的增删改查。下面是几个常见的SQL语句示例:
1. 数据插入
使用INSERT INTO语句将数据插入到表中。
例如,插入一个学生信息:
```
INSERT INTO student (name, age, gender) VALUES ('张三', 18, '男');
```
2. 数据查询
使用SELECT语句从表中查询数据。
例如,查询所有学生信息:
```
SELECT * FROM student;
```
3. 数据更新
使用UPDATE语句更新表中的数据。
例如,将学生“张三”的年龄改为20岁:
```
UPDATE student SET age = 20 WHERE name = '张三';
```
4. 数据删除
使用DELETE语句从表中删除数据。
例如,删除学生“张三”的信息:
```
DELETE FROM student WHERE name = '张三';
```
相关问题
python对数据库增删改查
Python中可以通过许多数据库API来实现对数据库的增删改查操作,其中比较常用的有:
1. MySQLdb:用于连接MySQL数据库的Python库
2. sqlite3:Python自带的轻量级数据库,适用于小型项目
3. psycopg2:用于连接PostgreSQL数据库的Python库
下面分别介绍如何使用这些库进行增删改查操作:
1. MySQLdb:
连接数据库:
```python
import MySQLdb
conn = MySQLdb.connect(host='localhost', user='root', passwd='password', db='database_name')
```
查询数据:
```python
cursor = conn.cursor()
cursor.execute("SELECT * FROM table_name")
result = cursor.fetchall()
```
插入数据:
```python
cursor = conn.cursor()
sql = "INSERT INTO table_name (column1, column2, column3) VALUES (%s, %s, %s)"
val = ("value1", "value2", "value3")
cursor.execute(sql, val)
conn.commit()
```
更新数据:
```python
cursor = conn.cursor()
sql = "UPDATE table_name SET column1 = %s WHERE column2 = %s"
val = ("new_value", "old_value")
cursor.execute(sql, val)
conn.commit()
```
删除数据:
```python
cursor = conn.cursor()
sql = "DELETE FROM table_name WHERE column1 = %s"
val = ("value_to_delete",)
cursor.execute(sql, val)
conn.commit()
```
2. sqlite3:
连接数据库:
```python
import sqlite3
conn = sqlite3.connect('database_name.db')
```
查询数据:
```python
cursor = conn.cursor()
cursor.execute("SELECT * FROM table_name")
result = cursor.fetchall()
```
插入数据:
```python
cursor = conn.cursor()
sql = "INSERT INTO table_name (column1, column2, column3) VALUES (?, ?, ?)"
val = ("value1", "value2", "value3")
cursor.execute(sql, val)
conn.commit()
```
更新数据:
```python
cursor = conn.cursor()
sql = "UPDATE table_name SET column1 = ? WHERE column2 = ?"
val = ("new_value", "old_value")
cursor.execute(sql, val)
conn.commit()
```
删除数据:
```python
cursor = conn.cursor()
sql = "DELETE FROM table_name WHERE column1 = ?"
val = ("value_to_delete",)
cursor.execute(sql, val)
conn.commit()
```
3. psycopg2:
连接数据库:
```python
import psycopg2
conn = psycopg2.connect(host='localhost', user='postgres', password='password', dbname='database_name')
```
查询数据:
```python
cursor = conn.cursor()
cursor.execute("SELECT * FROM table_name")
result = cursor.fetchall()
```
插入数据:
```python
cursor = conn.cursor()
sql = "INSERT INTO table_name (column1, column2, column3) VALUES (%s, %s, %s)"
val = ("value1", "value2", "value3")
cursor.execute(sql, val)
conn.commit()
```
更新数据:
```python
cursor = conn.cursor()
sql = "UPDATE table_name SET column1 = %s WHERE column2 = %s"
val = ("new_value", "old_value")
cursor.execute(sql, val)
conn.commit()
```
删除数据:
```python
cursor = conn.cursor()
sql = "DELETE FROM table_name WHERE column1 = %s"
val = ("value_to_delete",)
cursor.execute(sql, val)
conn.commit()
```
Flink自定义source function查询Postgres数据中的数据
您好,如果您需要自定义 Flink Source Function 从 PostgreSQL 中读取数据,可以按照以下步骤操作:
1. 在项目中添加 PostgreSQL JDBC 驱动,例如:
```xml
<dependency>
<groupId>org.postgresql</groupId>
<artifactId>postgresql</artifactId>
<version>42.2.12</version>
</dependency>
```
2. 实现 SourceFunction 接口,并在 run 方法中编写从 PostgreSQL 中读取数据的逻辑,例如:
```java
public class PostgresSourceFunction implements SourceFunction<Row> {
private final String url;
private final String username;
private final String password;
private final String query;
private volatile boolean isRunning = true;
public PostgresSourceFunction(String url, String username, String password, String query) {
this.url = url;
this.username = username;
this.password = password;
this.query = query;
}
@Override
public void run(SourceContext<Row> ctx) throws Exception {
Connection conn = null;
PreparedStatement stmt = null;
ResultSet rs = null;
try {
conn = DriverManager.getConnection(url, username, password);
stmt = conn.prepareStatement(query);
rs = stmt.executeQuery();
while (isRunning && rs.next()) {
// 将查询结果转化为 Flink 的 Row 类型
Row row = Row.of(rs.getInt(1), rs.getString(2), rs.getDouble(3));
// 发射数据到下游算子
ctx.collect(row);
}
} finally {
if (rs != null) {
rs.close();
}
if (stmt != null) {
stmt.close();
}
if (conn != null) {
conn.close();
}
}
}
@Override
public void cancel() {
isRunning = false;
}
}
```
在这个例子中,我们使用 JDBC 连接 PostgreSQL 数据库,并执行指定的查询语句,将查询结果转为 Flink 的 Row 类型,然后通过 SourceContext 发射数据到下游算子。
3. 在 Flink 程序中使用自定义的 Source Function,例如:
```java
String url = "jdbc:postgresql://localhost:5432/mydb";
String username = "myuser";
String password = "mypassword";
String query = "SELECT id, name, price FROM products";
DataStream<Row> stream = env.addSource(new PostgresSourceFunction(url, username, password, query));
```
在这个例子中,我们使用 addSource 方法将自定义的 PostgresSourceFunction 添加到 Flink 程序中,从而能够读取 PostgreSQL 数据库中的数据。