SQL 工具包

直接从命令行操作关系型数据库。涵盖 SQLite、PostgreSQL 和 MySQL，包含模式设计、查询、迁移、索引和操作的模式。

使用场景

• 创建或修改数据库模式
• 编写复杂查询（连接、聚合、窗口函数、CTE）
• 构建迁移脚本
• 通过索引和 EXPLAIN 优化慢查询
• 备份和恢复数据库
• 使用 SQLite 快速进行数据探索（零配置）

SQLite（零配置）

SQLite 随 Python 附带，并在每个系统上都可用。可用于本地数据、原型设计和单文件数据库。

快速开始

# 创建/打开数据库
sqlite3 mydb.sqlite

# 直接导入 CSV
sqlite3 mydb.sqlite ".mode csv" ".import data.csv mytable" "SELECT COUNT(*) FROM mytable;"

# 单行查询
sqlite3 mydb.sqlite "SELECT * FROM users WHERE created_at > '2026-01-01' LIMIT 10;"

# 导出到 CSV
sqlite3 -header -csv mydb.sqlite "SELECT * FROM orders;" > orders.csv

# 带标题和列格式的交互模式
sqlite3 -header -column mydb.sqlite

模式操作

-- 创建表
CREATE TABLE users (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    email TEXT NOT NULL UNIQUE,
    name TEXT NOT NULL,
    created_at TEXT DEFAULT (datetime('now')),
    updated_at TEXT DEFAULT (datetime('now'))
);

-- 创建带外键的表
CREATE TABLE orders (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
    total REAL NOT NULL CHECK(total >= 0),
    status TEXT NOT NULL DEFAULT 'pending' CHECK(status IN ('pending','paid','shipped','cancelled')),
    created_at TEXT DEFAULT (datetime('now'))
);

-- 添加列
ALTER TABLE users ADD COLUMN phone TEXT;

-- 创建索引
CREATE INDEX idx_orders_user_id ON orders(user_id);
CREATE UNIQUE INDEX idx_users_email ON users(email);

-- 查看模式
.schema users
.tables

PostgreSQL

连接

# 连接
psql -h localhost -U myuser -d mydb

# 连接字符串
psql "postgresql://user:pass@localhost:5432/mydb?sslmode=require"

# 运行单条查询
psql -h localhost -U myuser -d mydb -c "SELECT NOW();"

# 运行 SQL 文件
psql -h localhost -U myuser -d mydb -f migration.sql

# 列出数据库
psql -l

模式设计模式

-- 使用 UUID 作为分布式友好的主键
CREATE EXTENSION IF NOT EXISTS "uuid-ossp";

CREATE TABLE users (
    id UUID PRIMARY KEY DEFAULT uuid_generate_v4(),
    email TEXT NOT NULL,
    name TEXT NOT NULL,
    password_hash TEXT NOT NULL,
    role TEXT NOT NULL DEFAULT 'user' CHECK(role IN ('user','admin','moderator')),
    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    CONSTRAINT users_email_unique UNIQUE(email)
);

-- 自动更新 updated_at
CREATE OR REPLACE FUNCTION update_modified_column()
RETURNS TRIGGER AS $$
BEGIN
    NEW.updated_at = NOW();
    RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER update_users_modtime
    BEFORE UPDATE ON users
    FOR EACH ROW EXECUTE FUNCTION update_modified_column();

-- 枚举类型 (PostgreSQL 特有)
CREATE TYPE order_status AS ENUM ('pending', 'paid', 'shipped', 'delivered', 'cancelled');

CREATE TABLE orders (
    id UUID PRIMARY KEY DEFAULT uuid_generate_v4(),
    user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
    status order_status NOT NULL DEFAULT 'pending',
    total NUMERIC(10,2) NOT NULL CHECK(total >= 0),
    metadata JSONB DEFAULT '{}',
    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
);

-- 部分索引 (仅索引有效订单 — 更小、更快)
CREATE INDEX idx_orders_active ON orders(user_id, created_at)
    WHERE status NOT IN ('delivered', 'cancelled');

-- 用于 JSONB 查询的 GIN 索引
CREATE INDEX idx_orders_metadata ON orders USING GIN(metadata);

JSONB 查询 (PostgreSQL)

-- 存储 JSON
INSERT INTO orders (user_id, total, metadata)
VALUES ('...', 99.99, '{"source": "web", "coupon": "SAVE10", "items": [{"sku": "A1", "qty": 2}]}');

-- 查询 JSON 字段
SELECT * FROM orders WHERE metadata->>'source' = 'web';
SELECT * FROM orders WHERE metadata->'items' @> '[{"sku": "A1"}]';
SELECT metadata->>'coupon' AS coupon, COUNT(*) FROM orders GROUP BY 1;

-- 更新 JSON 字段
UPDATE orders SET metadata = jsonb_set(metadata, '{source}', '"mobile"') WHERE id = '...';

MySQL

连接

mysql -h localhost -u root -p mydb
mysql -h localhost -u root -p -e "SELECT NOW();" mydb

与PostgreSQL的主要区别

-- 自增 (不是 SERIAL)
CREATE TABLE users (
    id BIGINT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
    email VARCHAR(255) NOT NULL UNIQUE,
    name VARCHAR(255) NOT NULL,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

-- JSON 类型 (MySQL 5.7+)
CREATE TABLE orders (
    id BIGINT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
    user_id BIGINT UNSIGNED NOT NULL,
    metadata JSON,
    FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE
);

-- 查询 JSON
SELECT * FROM orders WHERE JSON_EXTRACT(metadata, '$.source') = 'web';
-- 或者简写:
SELECT * FROM orders WHERE metadata->>'$.source' = 'web';

查询模式

连接

-- 内连接 (仅匹配的行)
SELECT u.name, o.total, o.status
FROM users u
INNER JOIN orders o ON o.user_id = u.id
WHERE o.created_at > '2026-01-01';

-- 左连接 (所有用户，即使没有订单)
SELECT u.name, COUNT(o.id) AS order_count, COALESCE(SUM(o.total), 0) AS total_spent
FROM users u
LEFT JOIN orders o ON o.user_id = u.id
GROUP BY u.id, u.name;

-- 自连接 (查找具有相同电子邮件域的用户)
SELECT a.name, b.name, SPLIT_PART(a.email, '@', 2) AS domain
FROM users a
JOIN users b ON SPLIT_PART(a.email, '@', 2) = SPLIT_PART(b.email, '@', 2)
WHERE a.id < b.id;

聚合

-- 分组和 HAVING
SELECT status, COUNT(*) AS cnt, SUM(total) AS revenue
FROM orders
GROUP BY status
HAVING COUNT(*) > 10
ORDER BY revenue DESC;

-- 累计总和 (窗口函数)
SELECT date, revenue,
    SUM(revenue) OVER (ORDER BY date) AS cumulative_revenue
FROM daily_sales;

-- 组内排名
SELECT user_id, total,
    RANK() OVER (PARTITION BY user_id ORDER BY total DESC) AS rank
FROM orders;

-- 移动平均 (最近7条记录)
SELECT date, revenue,
    AVG(revenue) OVER (ORDER BY date ROWS BETWEEN 6 PRECEDING AND CURRENT ROW) AS ma_7
FROM daily_sales;

公共表表达式 (CTE)

-- 可读的多步骤查询
WITH monthly_revenue AS (
    SELECT DATE_TRUNC('month', created_at) AS month,
           SUM(total) AS revenue
    FROM orders
    WHERE status = 'paid'
    GROUP BY 1
),
growth AS (
    SELECT month, revenue,
           LAG(revenue) OVER (ORDER BY month) AS prev_revenue,
           ROUND((revenue - LAG(revenue) OVER (ORDER BY month)) /
                 NULLIF(LAG(revenue) OVER (ORDER BY month), 0) * 100, 1) AS growth_pct
    FROM monthly_revenue
)
SELECT * FROM growth ORDER BY month;

-- 递归 CTE (组织架构图 / 树遍历)
WITH RECURSIVE org_tree AS (
    SELECT id, name, manager_id, 0 AS depth
    FROM employees
    WHERE manager_id IS NULL
    UNION ALL
    SELECT e.id, e.name, e.manager_id, t.depth + 1
    FROM employees e
    JOIN org_tree t ON e.manager_id = t.id
)
SELECT REPEAT('  ', depth) || name AS org_chart FROM org_tree ORDER BY depth, name;

数据库迁移

手动迁移脚本模式

#!/bin/bash
# migrate.sh - 运行带编号的 SQL 迁移文件
DB_URL="${1:?用法: migrate.sh <数据库URL>}"
MIGRATIONS_DIR="./migrations"

# 创建跟踪表
psql "$DB_URL" -c "CREATE TABLE IF NOT EXISTS schema_migrations (
    version TEXT PRIMARY KEY,
    applied_at TIMESTAMPTZ DEFAULT NOW()
);"

# 按顺序运行待处理的迁移
for file in $(ls "$MIGRATIONS_DIR"/*.sql | sort); do
    version=$(basename "$file" .sql)
    already=$(psql "$DB_URL" -tAc "SELECT 1 FROM schema_migrations WHERE version='$version';")
    if [ "$already" = "1" ]; then
        echo "跳过: $version (已应用)"
        continue
    fi
    echo "应用: $version"
    psql "$DB_URL" -f "$file" && \
    psql "$DB_URL" -c "INSERT INTO schema_migrations (version) VALUES ('$version');" || {
        echo "失败: $version"
        exit 1
    }
done
echo "所有迁移已应用。"

迁移文件约定

migrations/
  001_create_users.sql
  002_create_orders.sql
  003_add_users_phone.sql
  004_add_orders_metadata_index.sql

每个文件：

-- 003_add_users_phone.sql
-- 升级操作
ALTER TABLE users ADD COLUMN phone TEXT;

-- 回滚操作: ALTER TABLE users DROP COLUMN phone;

查询优化

EXPLAIN (PostgreSQL)

-- 显示查询计划
EXPLAIN SELECT * FROM orders WHERE user_id = '...' AND status = 'paid';

-- 显示实际执行时间
EXPLAIN (ANALYZE, BUFFERS, FORMAT TEXT)
SELECT * FROM orders WHERE user_id = '...' AND status = 'paid';

需要注意的地方：

• 顺序扫描在大表上 → 需要索引
• 嵌套循环处理大量行时 → 考虑哈希连接（可能需要更多work_mem）
• 过滤移除的行数过高 → 索引未覆盖过滤条件
• 实际行数与估计值相差甚远 → 运行ANALYZE 表名;以更新统计信息

索引策略

-- 单列索引（最常用）
CREATE INDEX idx_orders_user_id ON orders(user_id);

-- 复合索引（用于同时过滤多列的查询）
CREATE INDEX idx_orders_user_status ON orders(user_id, status);
-- 列顺序很重要：将等值过滤的列放在前面，范围过滤的列放在最后

-- 覆盖索引（包含数据列以避免回表查询）
CREATE INDEX idx_orders_covering ON orders(user_id, status) INCLUDE (total, created_at);

-- 部分索引（更小、更快——只索引查询所需的数据）
CREATE INDEX idx_orders_pending ON orders(user_id) WHERE status = 'pending';

-- 检查未使用的索引
SELECT schemaname, tablename, indexname, idx_scan
FROM pg_stat_user_indexes
WHERE idx_scan = 0 AND indexname NOT LIKE '%pkey%'
ORDER BY pg_relation_size(indexrelid) DESC;

SQLite 执行计划

EXPLAIN QUERY PLAN SELECT * FROM orders WHERE user_id = 5;
-- 注意：SCAN（差） vs SEARCH USING INDEX（好）

备份与恢复

PostgreSQL

# 完整转储（自定义格式，压缩）
pg_dump -Fc -h localhost -U myuser mydb > backup.dump

# 恢复
pg_restore -h localhost -U myuser -d mydb --clean --if-exists backup.dump

# SQL 转储（可移植，可读）
pg_dump -h localhost -U myuser mydb > backup.sql

# 转储特定表
pg_dump -h localhost -U myuser -t users -t orders mydb > partial.sql

# 将表复制为 CSV
psql -c "\copy (SELECT * FROM users) TO 'users.csv' CSV HEADER"

SQLite

# 备份（仅复制文件，但使用 .backup 以保持一致性）
sqlite3 mydb.sqlite ".backup backup.sqlite"

# 导出为 SQL
sqlite3 mydb.sqlite .dump > backup.sql

# 从 SQL 恢复
sqlite3 newdb.sqlite < backup.sql

MySQL

# 导出
mysqldump -h localhost -u root -p mydb > backup.sql

# 恢复
mysql -h localhost -u root -p mydb < backup.sql

提示

• 在应用程序代码中始终使用参数化查询 —— 切勿将用户输入直接拼接到 SQL 语句中
• 在 PostgreSQL 中处理含时区的日期时使用TIMESTAMPTZ（而非TIMESTAMP）
• 在 SQLite 中设置PRAGMA journal_mode=WAL;以提升并发读取性能
• 部署任何在大表上运行的查询前，先使用EXPLAIN进行分析
• PostgreSQL：\d+ 表名可显示列、索引及表大小\di+列出所有索引及其大小
• 如需快速数据探索，可将任意 CSV 导入 SQLite：sqlite3 :memory: ".mode csv" ".import 文件.csv t" "SELECT ..."