SQL经典50题答案

<code class="sql">CREATE DATABASE my_database;</code>

<code class="sql">CREATE TABLE my_table (
    id INTEGER PRIMARY KEY,
    name TEXT,
    age INTEGER
);</code>

<code class="sql">INSERT INTO my_table (id, name, age) VALUES (1, 'John', 30);</code>

<code class="sql">SELECT * FROM my_table;</code>

<code class="sql">UPDATE my_table SET name = 'John Doe' WHERE id = 1;</code>

<code class="sql">DELETE FROM my_table WHERE id = 1;</code>

<code class="sql">SELECT * FROM my_table ORDER BY name;</code>

<code class="sql">SELECT * FROM my_table WHERE age > 30;</code>

<code class="sql">SELECT age, COUNT(*) AS count FROM my_table GROUP BY age;</code>

<code class="sql">SELECT SUM(age) FROM my_table;</code>

<code class="sql">SELECT * FROM customers c JOIN orders o ON c.id = o.customer_id;</code>

<code class="sql">SELECT * FROM my_table WHERE id IN (SELECT id FROM my_second_table);</code>

<code class="sql">SELECT * FROM my_table WHERE EXISTS (SELECT 1 FROM my_second_table WHERE id = my_table.id);</code>

<code class="sql">SELECT * FROM my_table WHERE NOT EXISTS (SELECT 1 FROM my_second_table WHERE id = my_table.id);</code>

<code class="sql">SELECT * FROM my_table UNION SELECT * FROM my_second_table;</code>

<code class="sql">SELECT * FROM my_table INTERSECT SELECT * FROM my_second_table;</code>

<code class="sql">SELECT * FROM my_table EXCEPT SELECT * FROM my_second_table;</code>

<code class="sql">SELECT * FROM my_table WHERE name LIKE '%John%';</code>

<code class="sql">SELECT * FROM my_table WHERE age BETWEEN 20 AND 30;</code>

<code class="sql">SELECT * FROM my_table WHERE age IS NULL;</code>

<code class="sql">ALTER TABLE my_table ADD FOREIGN KEY (customer_id) REFERENCES customers (id);</code>

<code class="sql">ALTER TABLE my_table ADD UNIQUE INDEX (name);</code>

<code class="sql">ALTER TABLE my_table ADD PRIMARY KEY (id);</code>

<code class="sql">BEGIN TRANSACTION;
-- 执行一系列查询
COMMIT;</code>

<code class="sql">CREATE PROCEDURE my_procedure (IN param1 INT) AS
BEGIN
    -- 存储过程代码
END;</code>

<code class="sql">CREATE FUNCTION my_function (param1 INT) RETURNS INT AS
BEGIN
    -- 函数代码
END;</code>

<code class="sql">CREATE VIEW my_view AS
SELECT * FROM my_table;</code>

<code class="sql">DECLARE cursor_name CURSOR FOR
SELECT * FROM my_table;</code>

<code class="sql">CREATE TRIGGER my_trigger ON my_table FOR DELETE AS
BEGIN
    -- 触发器代码
END;</code>

<code class="sql">INT (整型)
TEXT (文本)
FLOAT (浮点数)
DATE (日期)
TIME (时间)
DATETIME (日期时间)</code>

<code class="sql">+ (加法)
- (减法)
* (乘法)
/ (除法)
% (模运算)</code>

<code class="sql">SUM() (求和)
AVG() (求平均值)
MIN() (求最小值)
MAX() (求最大值)</code>

<code class="sql">SELECT (选择)
FROM (从)
WHERE (条件)
ORDER BY (排序)
LIMIT (限制)</code>

<code class="sql">INSERT (插入)
UPDATE (更新)
DELETE (删除)</code>

<code class="sql">CREATE (创建)
DROP (删除)
ALTER (修改)</code>

<code class="sql">GRANT (授予)
REVOKE (撤销)</code>

<code class="sql">INNER JOIN (内部连接)
LEFT JOIN (左连接)
RIGHT JOIN (右连接)
FULL JOIN (全连接)</code>

<code class="sql">使用索引
避免嵌套查询
使用 LIMIT 子句</code>

<code class="sql">使用强密码
启用身份验证
使用加密</code>

<code class="sql">MySQL Workbench
phpMyAdmin
Navicat</code>

<code class="sql">MySQL 文档
Stack Overflow
W3Schools</code>

<code class="sql">MySQL 8.0
MySQL 5.7
MariaDB</code>

<code class="sql">语法错误
表不存在
列不存在
权限不足</code>

<code class="sql">使用 EXPLAIN 命令
检查错误日志
使用调试器</code>

<code class="sql">使用规范化的模式
编写高效的查询
备份你的数据库
保持你的数据库更新</code>

<code class="sql">云数据库
NoSQL 数据库
机器学习</code>

<code class="sql">SELECT ... FOR UPDATE;</code>