PGSQL常见命令行与函数实例详解

# 基本连接（使用当前系统用户）
psql
# 连接指定数据库
psql -d mydatabase
# 连接指定用户和数据库
psql -U username -d mydatabase
# 连接远程数据库
psql -h hostname -p 5432 -U username -d mydatabase
# 连接并执行SQL文件
psql -d mydatabase -f script.sql
# 连接并执行单条命令
psql -d mydatabase -c "SELECT version();"

-- 列出所有数据库
\l
\l+
-- 连接/切换数据库
\c database_name
\connect database_name
-- 创建数据库
CREATE DATABASE newdb;
-- 删除数据库
DROP DATABASE olddb;

-- 列出当前数据库所有表
\dt
\dt+
-- 描述表结构
\d table_name
\d+ table_name
-- 列出所有索引
\di
\di+
-- 列出所有序列
\ds
\ds+

-- 列出所有模式
\dn
\dn+
-- 设置搜索路径
SET search_path TO schema1, schema2;
-- 查看当前搜索路径
SHOW search_path;

-- 列出所有用户/角色
\du
\du+
-- 查看当前用户
SELECT current_user;
-- 查看用户权限
\dp table_name
\z table_name

-- 查看服务器版本
SELECT version();
-- 查看连接信息
\conninfo
-- 查看当前数据库
SELECT current_database();
-- 查看当前模式
SELECT current_schema();

-- 扩展显示（行转列）
\x on
\x auto
\x off
-- 设置输出格式
\a (对齐切换)
\f (字段分隔符)
-- 计时开关
\timing on
\timing off
-- 输出到文件
\o filename.txt
\o

-- 绝对值
SELECT abs(-15); -- 15
-- 四舍五入
SELECT round(3.14159, 2); -- 3.14
SELECT round(123.456); -- 123
-- 取整函数
SELECT ceil(3.14); -- 4 (向上取整)
SELECT floor(3.14); -- 3 (向下取整)
SELECT trunc(3.14159, 2); -- 3.14 (截断)
-- 幂运算
SELECT power(2, 3); -- 8
SELECT sqrt(25); -- 5 (平方根)
SELECT cbrt(27); -- 3 (立方根)
-- 对数函数
SELECT ln(10); -- 自然对数
SELECT log(100); -- 以10为底对数

SELECT pi(); -- 3.14159265358979
SELECT sin(pi()/2); -- 1
SELECT cos(0); -- 1
SELECT tan(pi()/4); -- 1
SELECT degrees(pi()); -- 180 (弧度转角度)
SELECT radians(180); -- 3.14159 (角度转弧度)

SELECT random(); -- 0-1之间的随机数
SELECT setseed(0.5); -- 设置随机种子
-- 生成指定范围随机整数
SELECT floor(random() * 100)::int; -- 0-99随机整数
SELECT (random() * (max-min) + min)::int; -- min-max随机整数

-- 长度和位置
SELECT length('Hello'); -- 5
SELECT position('l' in 'Hello'); -- 3
SELECT strpos('Hello', 'l'); -- 3
-- 大小写转换
SELECT upper('hello'); -- HELLO
SELECT lower('HELLO'); -- hello
SELECT initcap('hello world'); -- Hello World
-- 修剪函数
SELECT trim('  hello  '); -- 'hello'
SELECT ltrim('  hello'); -- 'hello'
SELECT rtrim('hello  '); -- 'hello'
SELECT trim(BOTH 'x' FROM 'xxhelloxx'); -- 'hello'
-- 填充函数
SELECT lpad('hi', 5, '*'); -- '***hi'
SELECT rpad('hi', 5, '*'); -- 'hi***'

-- 子字符串
SELECT substring('Hello World' from 2 for 5); -- 'ello '
SELECT substr('Hello World', 2, 5); -- 'ello '
-- 字符串替换
SELECT replace('Hello World', 'World', 'PostgreSQL'); -- 'Hello PostgreSQL'
SELECT translate('12345', '123', 'abc'); -- 'abc45'
-- 字符串分割
SELECT split_part('a,b,c,d', ',', 2); -- 'b'
SELECT string_to_array('a,b,c', ','); -- {a,b,c}
SELECT array_to_string(ARRAY['a','b','c'], ','); -- 'a,b,c'

-- 字符串连接
SELECT concat('Hello', ' ', 'World'); -- 'Hello World'
SELECT 'Hello' || ' ' || 'World'; -- 'Hello World'
-- 格式化输出
SELECT format('Hello %s, your balance is %s', 'John', 100.50);
-- 'Hello John, your balance is 100.50'
-- 重复字符串
SELECT repeat('*', 5); -- '*****'

-- 获取当前时间
SELECT current_date; -- 当前日期
SELECT current_time; -- 当前时间
SELECT current_timestamp; -- 当前时间戳
SELECT now(); -- 当前时间戳（同current_timestamp）
SELECT localtimestamp; -- 本地时间戳
-- 带精度的当前时间
SELECT current_time(2); -- 当前时间（2位小数秒）
SELECT current_timestamp(3); -- 当前时间戳（3位小数秒）

-- EXTRACT函数
SELECT extract(year FROM current_timestamp); -- 年份
SELECT extract(month FROM current_timestamp); -- 月份
SELECT extract(day FROM current_timestamp); -- 日期
SELECT extract(hour FROM current_timestamp); -- 小时
SELECT extract(minute FROM current_timestamp); -- 分钟
SELECT extract(second FROM current_timestamp); -- 秒数
SELECT extract(dow FROM current_timestamp); -- 星期几（0-6，周日=0）
SELECT extract(doy FROM current_timestamp); -- 一年中的第几天
-- DATE_PART函数（同EXTRACT）
SELECT date_part('year', current_timestamp);

-- 日期加减
SELECT current_date + INTERVAL '1 day'; -- 明天
SELECT current_date - INTERVAL '1 week'; -- 一周前
SELECT current_timestamp + INTERVAL '2 hours 30 minutes'; -- 2小时30分钟后
-- 年龄计算
SELECT age('2000-01-01'::date); -- 从2000-01-01到现在的年龄
SELECT age('2000-01-01'::date, '2020-01-01'::date); -- 两个日期之间的年龄
-- 日期截断
SELECT date_trunc('hour', current_timestamp); -- 截断到小时
SELECT date_trunc('day', current_timestamp); -- 截断到天
SELECT date_trunc('month', current_timestamp); -- 截断到月

-- TO_CHAR格式化
SELECT to_char(current_timestamp, 'YYYY-MM-DD HH24:MI:SS'); -- '2023-01-01 14:30:00'
SELECT to_char(current_timestamp, 'Day, Month DD, YYYY'); -- 'Sunday, January 01, 2023'
SELECT to_char(123.45, '999D99'); -- '123.45'
-- TO_DATE和TO_TIMESTAMP转换
SELECT to_date('20230101', 'YYYYMMDD'); -- 2023-01-01
SELECT to_timestamp('20230101 143000', 'YYYYMMDD HH24MISS'); -- 2023-01-01 14:30:00

-- CASE表达式
SELECT 
    name,
    salary,
    CASE 
        WHEN salary > 100000 THEN 'High'
        WHEN salary > 50000 THEN 'Medium'
        ELSE 'Low'
    END as salary_level
FROM employees;
-- 简单CASE
SELECT 
    product_type,
    CASE product_type
        WHEN 'A' THEN 'Type A'
        WHEN 'B' THEN 'Type B'
        ELSE 'Other'
    END as type_description
FROM products;

-- COALESCE（返回第一个非空值）
SELECT coalesce(NULL, NULL, 'default'); -- 'default'
SELECT coalesce(email, 'N/A') FROM users; -- 如果email为NULL则返回'N/A'
-- NULLIF（相等返回NULL）
SELECT nullif(5, 5); -- NULL
SELECT nullif(5, 0); -- 5
-- GREATEST和LEAST
SELECT greatest(1, 5, 3); -- 5
SELECT least(1, 5, 3); -- 1

-- 计数
SELECT count(*) FROM table; -- 总行数
SELECT count(DISTINCT column) FROM table; -- 不重复计数
-- 求和与平均
SELECT sum(salary) FROM employees;
SELECT avg(salary) FROM employees;
-- 最大最小值
SELECT max(salary) FROM employees;
SELECT min(salary) FROM employees;
-- 统计信息
SELECT stddev(salary) FROM employees; -- 标准差
SELECT variance(salary) FROM employees; -- 方差

-- 分组统计
SELECT 
    department,
    count(*) as emp_count,
    avg(salary) as avg_salary,
    sum(salary) as total_salary
FROM employees 
GROUP BY department;
-- 字符串聚合
SELECT 
    department,
    string_agg(name, ', ') as employees
FROM employees 
GROUP BY department;
-- 数组聚合
SELECT 
    department,
    array_agg(name) as employees
FROM employees 
GROUP BY department;
-- JSON聚合
SELECT 
    department,
    json_agg(json_build_object('name', name, 'salary', salary)) as employees
FROM employees 
GROUP BY department;

-- 行号、排名、密集排名
SELECT 
    name,
    salary,
    row_number() OVER (ORDER BY salary DESC) as row_num,
    rank() OVER (ORDER BY salary DESC) as rank,
    dense_rank() OVER (ORDER BY salary DESC) as dense_rank
FROM employees;
-- 分区排名
SELECT 
    department,
    name,
    salary,
    rank() OVER (PARTITION BY department ORDER BY salary DESC) as dept_rank
FROM employees;

-- LAG和LEAD（访问前后行）
SELECT 
    date,
    sales,
    lag(sales) OVER (ORDER BY date) as prev_sales,
    lead(sales) OVER (ORDER BY date) as next_sales
FROM sales_data;
-- FIRST_VALUE和LAST_VALUE
SELECT 
    date,
    sales,
    first_value(sales) OVER (ORDER BY date) as first_sales,
    last_value(sales) OVER (ORDER BY date) as last_sales
FROM sales_data;

-- 累计计算
SELECT 
    date,
    sales,
    sum(sales) OVER (ORDER BY date) as cumulative_sum,
    avg(sales) OVER (ORDER BY date) as cumulative_avg
FROM sales_data;
-- 移动平均
SELECT 
    date,
    sales,
    avg(sales) OVER (ORDER BY date ROWS BETWEEN 2 PRECEDING AND CURRENT ROW) as moving_avg_3
FROM sales_data;

-- 创建JSON
SELECT json_build_object('name', 'John', 'age', 30);
SELECT json_build_array(1, 2, 3);
-- 解析JSON
SELECT json_extract_path('{"a": {"b": 1}}', 'a', 'b'); -- 1
SELECT '{"name": "John"}'::json->>'name'; -- 'John'
SELECT '{"ages": [10, 20, 30]}'::json->'ages'->>1; -- '20'

-- 行转JSON
SELECT row_to_json(employees) FROM employees WHERE id = 1;
-- JSON聚合
SELECT 
    department,
    json_agg(json_build_object('name', name, 'salary', salary)) as employees
FROM employees 
GROUP BY department;

# 备份单个数据库
pg_dump -U username -d mydatabase -f backup.sql
# 备份所有数据库
pg_dumpall -U username -f alldb_backup.sql
# 压缩备份
pg_dump -U username -d mydatabase | gzip > backup.sql.gz
# 恢复数据库
psql -U username -d mydatabase -f backup.sql
# 恢复压缩备份
gunzip -c backup.sql.gz | psql -U username -d mydatabase

-- 查看查询计划
EXPLAIN SELECT * FROM large_table WHERE id = 1000;
EXPLAIN ANALYZE SELECT * FROM large_table WHERE id = 1000;
-- 查看表大小和索引
SELECT 
    schemaname,
    tablename,
    tableowner,
    tablesize,
    indexsize
FROM pg_tables 
WHERE schemaname = 'public';
-- 查看长查询
SELECT 
    pid, 
    now() - pg_stat_activity.query_start AS duration, 
    query 
FROM pg_stat_activity 
WHERE state = 'active' 
ORDER BY duration DESC;

-- 查看锁信息
SELECT 
    locktype, 
    relation::regclass, 
    mode, 
    granted 
FROM pg_locks 
WHERE relation = 'mytable'::regclass;
-- 查看连接数
SELECT 
    datname, 
    count(*) as connections 
FROM pg_stat_activity 
GROUP BY datname;
-- 查看表统计信息
SELECT 
    schemaname,
    tablename,
    seq_scan,
    seq_tup_read,
    idx_scan,
    idx_tup_fetch
FROM pg_stat_user_tables;