{"id":219,"date":"2025-05-27T18:53:37","date_gmt":"2025-05-27T10:53:37","guid":{"rendered":"https:\/\/zd1269878.noblogs.org\/?p=219"},"modified":"2025-10-21T10:31:34","modified_gmt":"2025-10-21T02:31:34","slug":"sql%ef%bc%88structured-query-language%ef%bc%89","status":"publish","type":"post","link":"https:\/\/zd1269878.noblogs.org\/en-US\/post\/2025\/05\/27\/sql%ef%bc%88structured-query-language%ef%bc%89\/","title":{"rendered":"SQL\uff08Structured Query Language\uff09"},"content":{"rendered":"\n
\n\n\n\n

\u4e00\u3001\u6570\u636e\u5b9a\u4e49\u8bed\u8a00\uff08DDL<\/a>\uff09<\/h2>\n\n\n\n

\u7528\u4e8e\u5b9a\u4e49\u548c\u7ba1\u7406\u6570\u636e\u5e93\u5bf9\u8c61\uff08\u5982\u8868\u3001\u7d22\u5f15\u3001\u89c6\u56fe\u7b49\uff09\u3002<\/p>\n\n\n\n

1. <\/a>CREATE\uff1a\u521b\u5efa\u6570\u636e\u5e93\u5bf9\u8c61<\/h3>\n\n\n\n

— \u521b\u5efa\u6570\u636e\u5e93
CREATE DATABASE database_name;

— \u521b\u5efa\u8868
CREATE TABLE table_name (
    column1 datatype constraints,
    column2 datatype constraints,
    …
);

— \u793a\u4f8b\uff1a\u521b\u5efa\u4e00\u4e2a\u5458\u5de5\u8868
CREATE TABLE employees (
    id INT PRIMARY KEY AUTO_INCREMENT,  — \u4e3b\u952e\uff0c\u81ea\u589e
    name VARCHAR(100) NOT NULL,         — \u975e\u7a7a\u5b57\u7b26\u4e32
    age INT CHECK (age >= 0),           — \u68c0\u67e5\u7ea6\u675f
    department_id INT,
    salary DECIMAL(10, 2) DEFAULT 0.00  — \u9ed8\u8ba4\u503c
);<\/p>\n\n\n\n

2. <\/a>ALTER\uff1a\u4fee\u6539\u6570\u636e\u5e93\u5bf9\u8c61<\/h3>\n\n\n\n

— \u6dfb\u52a0\u5217
ALTER TABLE table_name ADD column_name datatype;

— \u5220\u9664\u5217
ALTER TABLE table_name DROP COLUMN column_name;

— \u4fee\u6539\u5217\u7684\u6570\u636e\u7c7b\u578b\uff08\u5177\u4f53\u8bed\u6cd5\u56e0\u6570\u636e\u5e93\u800c\u5f02\uff09
ALTER TABLE table_name MODIFY column_name new_datatype;

— \u793a\u4f8b\uff1a\u4e3a employees \u8868\u6dfb\u52a0 email \u5217
ALTER TABLE employees ADD email VARCHAR(255);<\/p>\n\n\n\n

3. <\/a>DROP\uff1a\u5220\u9664\u6570\u636e\u5e93\u5bf9\u8c61<\/h3>\n\n\n\n

— \u5220\u9664\u8868
DROP TABLE table_name;

— \u5220\u9664\u6570\u636e\u5e93
DROP DATABASE database_name;

— \u793a\u4f8b\uff1a\u5220\u9664 employees \u8868
DROP TABLE employees;<\/p>\n\n\n\n

\n\n\n\n

\u4e8c\u3001\u6570\u636e\u64cd\u4f5c\u8bed\u8a00\uff08DML<\/a>\uff09<\/h2>\n\n\n\n

\u7528\u4e8e\u64cd\u4f5c\u6570\u636e\u5e93\u4e2d\u7684\u6570\u636e\uff08\u589e\u5220\u6539\uff09\u3002<\/p>\n\n\n\n

1. <\/a>INSERT\uff1a\u63d2\u5165\u6570\u636e<\/h3>\n\n\n\n

— \u63d2\u5165\u5b8c\u6574\u884c
INSERT INTO table_name (column1, column2, …)
VALUES (value1, value2, …);

— \u63d2\u5165\u90e8\u5206\u5217
INSERT INTO table_name (column1, column2)
VALUES (value1, value2);

— \u63d2\u5165\u591a\u884c
INSERT INTO table_name (column1, column2)
VALUES
    (value1, value2),
    (value3, value4);

— \u793a\u4f8b\uff1a\u63d2\u5165\u5458\u5de5\u6570\u636e
INSERT INTO employees (name, age, department_id, salary)
VALUES ('Alice', 30, 1, 5000.00);<\/p>\n\n\n\n

2. <\/a>UPDATE\uff1a\u66f4\u65b0\u6570\u636e<\/h3>\n\n\n\n

— \u66f4\u65b0\u8868\u4e2d\u6ee1\u8db3\u6761\u4ef6\u7684\u8bb0\u5f55
UPDATE table_name
SET column1 = value1, column2 = value2, …
WHERE condition;

— \u793a\u4f8b\uff1a\u5c06\u90e8\u95e8ID\u4e3a1\u7684\u5458\u5de5\u5de5\u8d44\u589e\u52a010%
UPDATE employees
SET salary = salary * 1.10
WHERE department_id = 1;<\/p>\n\n\n\n

3. <\/a>DELETE\uff1a\u5220\u9664\u6570\u636e<\/h3>\n\n\n\n

— \u5220\u9664\u6ee1\u8db3\u6761\u4ef6\u7684\u8bb0\u5f55
DELETE FROM table_name
WHERE condition;

— \u5220\u9664\u6240\u6709\u8bb0\u5f55\uff08\u4fdd\u7559\u8868\u7ed3\u6784\uff09
DELETE FROM table_name;

— \u793a\u4f8b\uff1a\u5220\u9664\u5e74\u9f84\u5927\u4e8e60\u7684\u5458\u5de5
DELETE FROM employees
WHERE age > 60;<\/p>\n\n\n\n

\n\n\n\n

\u4e09\u3001\u6570\u636e\u67e5\u8be2\u8bed\u8a00\uff08DQL<\/a>\uff09<\/h2>\n\n\n\n

\u7528\u4e8e\u4ece\u6570\u636e\u5e93\u4e2d\u67e5\u8be2\u6570\u636e\u3002<\/p>\n\n\n\n

1. <\/a>SELECT\uff1a\u57fa\u672c\u67e5\u8be2<\/h3>\n\n\n\n

— \u67e5\u8be2\u6240\u6709\u5217
SELECT * FROM table_name;

— \u67e5\u8be2\u6307\u5b9a\u5217
SELECT column1, column2 FROM table_name;

— \u53bb\u91cd\u67e5\u8be2
SELECT DISTINCT column_name FROM table_name;

— \u793a\u4f8b\uff1a\u67e5\u8be2\u6240\u6709\u5458\u5de5\u59d3\u540d\u548c\u5de5\u8d44
SELECT name, salary FROM employees;<\/p>\n\n\n\n

2. <\/a>WHERE\uff1a\u6761\u4ef6\u8fc7\u6ee4<\/h3>\n\n\n\n

— \u4f7f\u7528\u6bd4\u8f83\u8fd0\u7b97\u7b26\uff08=, <>, >, <, >=, <=\uff09
SELECT * FROM table_name
WHERE column > value;

— \u903b\u8f91\u8fd0\u7b97\u7b26\uff08AND, OR, NOT\uff09
SELECT * FROM employees
WHERE age > 25 AND department_id = 2;

— \u8303\u56f4\u67e5\u8be2\uff08BETWEEN\uff09
SELECT * FROM employees
WHERE salary BETWEEN 3000 AND 5000;

— \u96c6\u5408\u67e5\u8be2\uff08IN\uff09
SELECT * FROM employees
WHERE department_id IN (1, 2, 3);

— \u6a21\u7cca\u5339\u914d\uff08LIKE\uff09
SELECT * FROM employees
WHERE name LIKE 'A%';  — \u4ee5A\u5f00\u5934\u7684\u540d\u5b57<\/p>\n\n\n\n

3. <\/a>JOIN\uff1a\u591a\u8868\u8fde\u63a5<\/h3>\n\n\n\n

— \u5185\u8fde\u63a5\uff08INNER JOIN\uff09
SELECT employees.name, departments.name
FROM employees
INNER JOIN departments ON employees.department_id = departments.id;

— \u5de6\u8fde\u63a5\uff08LEFT JOIN\uff09
SELECT employees.name, departments.name
FROM employees
LEFT JOIN departments ON employees.department_id = departments.id;

— \u53f3\u8fde\u63a5\uff08RIGHT JOIN\uff09
SELECT employees.name, departments.name
FROM employees
RIGHT JOIN departments ON employees.department_id = departments.id;

— \u5168\u8fde\u63a5\uff08FULL JOIN\uff09
SELECT employees.name, departments.name
FROM employees
FULL JOIN departments ON employees.department_id = departments.id;<\/p>\n\n\n\n

4. <\/a>\u805a\u5408\u51fd\u6570\u4e0e\u5206\u7ec4<\/h3>\n\n\n\n

— \u805a\u5408\u51fd\u6570
SELECT COUNT(*) AS total, AVG(salary), MAX(salary), MIN(salary)
FROM employees;

— \u5206\u7ec4\u67e5\u8be2\uff08GROUP BY\uff09
SELECT department_id, AVG(salary) AS avg_salary
FROM employees
GROUP BY department_id;

— \u5206\u7ec4\u8fc7\u6ee4\uff08HAVING\uff09
SELECT department_id, COUNT(*) AS num_employees
FROM employees
GROUP BY department_id
HAVING COUNT(*) > 5;<\/p>\n\n\n\n

5. <\/a>\u6392\u5e8f\u4e0e\u5206\u9875<\/h3>\n\n\n\n

— \u6392\u5e8f\uff08ORDER BY\uff09
SELECT * FROM employees
ORDER BY salary DESC;  — \u964d\u5e8f\u6392\u5217

— \u5206\u9875\uff08LIMIT \u548c OFFSET\uff09
SELECT * FROM employees
LIMIT 10 OFFSET 20;  — \u4ece\u7b2c21\u6761\u5f00\u59cb\u53d610\u6761\u8bb0\u5f55<\/p>\n\n\n\n

\n\n\n\n

\u56db\u3001\u6570\u636e\u63a7\u5236\u8bed\u8a00\uff08DCL<\/a>\uff09<\/h2>\n\n\n\n

\u7528\u4e8e\u7ba1\u7406\u6570\u636e\u5e93\u6743\u9650\u3002<\/p>\n\n\n\n

1. <\/a>GRANT\uff1a\u6388\u4e88\u6743\u9650<\/h3>\n\n\n\n

— \u6388\u4e88\u7528\u6237\u5bf9\u8868\u7684\u67e5\u8be2\u6743\u9650
GRANT SELECT ON table_name TO 'username'@'host';

— \u6388\u4e88\u6240\u6709\u6743\u9650
GRANT ALL PRIVILEGES ON database_name.* TO 'username'@'host';<\/p>\n\n\n\n

2. <\/a>REVOKE\uff1a\u64a4\u9500\u6743\u9650<\/h3>\n\n\n\n

— \u64a4\u9500\u7528\u6237\u7684\u66f4\u65b0\u6743\u9650
REVOKE UPDATE ON table_name FROM 'username'@'host';

— \u5237\u65b0\u6743\u9650
FLUSH PRIVILEGES;<\/p>\n\n\n\n

\n\n\n\n

\u4e94\u3001\u5e38\u7528\u51fd\u6570<\/a><\/h2>\n\n\n\n

1. <\/a>\u5b57\u7b26\u4e32\u51fd\u6570<\/h3>\n\n\n\n

SELECT CONCAT('Hello', ' ', 'World');  — \u8fde\u63a5\u5b57\u7b26\u4e32
SELECT UPPER('hello');                 — \u8f6c\u5927\u5199
SELECT SUBSTRING('Hello World', 1, 5); — \u53d6\u5b50\u4e32<\/p>\n\n\n\n

2. <\/a>\u65e5\u671f\u51fd\u6570<\/h3>\n\n\n\n

SELECT NOW();                          — \u5f53\u524d\u65e5\u671f\u548c\u65f6\u95f4
SELECT DATE_ADD('2023-01-01', INTERVAL 1 DAY);  — \u65e5\u671f\u52a0\u51cf
SELECT DATEDIFF('2023-01-10', '2023-01-01');    — \u65e5\u671f\u5dee<\/p>\n\n\n\n

3. <\/a>\u6570\u5b66\u51fd\u6570<\/h3>\n\n\n\n

SELECT ROUND(3.14159, 2);  — \u56db\u820d\u4e94\u5165
SELECT RAND();             — \u968f\u673a\u6570
SELECT ABS(-10);           — \u7edd\u5bf9\u503c<\/p>\n\n\n\n

\n\n\n\n

\u516d\u3001\u6ce8\u610f\u4e8b\u9879<\/a><\/h2>\n\n\n\n
    \n
  1. \u5173\u952e\u5b57\u5927\u5c0f\u5199<\/strong>\uff1aSQL \u5173\u952e\u5b57\u4e0d\u533a\u5206\u5927\u5c0f\u5199\uff08\u5982 SELECT \u548c select \u7b49\u6548\uff09\uff0c\u4f46\u901a\u5e38\u4f7f\u7528\u5927\u5199\u4ee5\u589e\u5f3a\u53ef\u8bfb\u6027\u3002<\/li>\n\n\n\n
  2. \u5f15\u53f7<\/strong>\uff1a\u5b57\u7b26\u4e32\u7528\u5355\u5f15\u53f7 '\uff0c\u5217\u540d\u548c\u8868\u540d\u901a\u5e38\u4e0d\u7528\u5f15\u53f7\uff08\u9664\u975e\u5305\u542b\u7279\u6b8a\u5b57\u7b26\uff09\u3002<\/li>\n\n\n\n
  3. \u901a\u914d\u7b26<\/strong>\uff1a% \u5339\u914d\u4efb\u610f\u6570\u91cf\u5b57\u7b26\uff0c_ \u5339\u914d\u5355\u4e2a\u5b57\u7b26\u3002<\/li>\n\n\n\n
  4. \u522b\u540d<\/strong>\uff1a\u4f7f\u7528 AS \u4e3a\u5217\u6216\u8868\u8d77\u522b\u540d\uff08\u5982 SELECT name AS emp_name\uff09\u3002<\/li>\n\n\n\n
  5. NULL <\/strong>\u503c<\/strong>\uff1a\u4f7f\u7528 IS NULL \u6216 IS NOT NULL \u5224\u65ad\u7a7a\u503c\u3002<\/li>\n\n\n\n
  6. \u4e8b\u52a1\u63a7\u5236<\/strong>\uff1a<\/li>\n\n\n\n
  7. START TRANSACTION;\u00a0 — \u5f00\u59cb\u4e8b\u52a1
    COMMIT;\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 — \u63d0\u4ea4\u4e8b\u52a1
    ROLLBACK;\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 — \u56de\u6eda\u4e8b\u52a1<\/li>\n\n\n\n
  8. \u5b89\u5168\u6027<\/strong>\uff1a\u907f\u514d\u76f4\u63a5\u4f7f\u7528 DROP \u6216 DELETE \u65f6\u4e0d\u52a0 WHERE \u6761\u4ef6\u3002<\/li>\n<\/ol>\n\n\n\n
    \n\n\n\n

    \u4e03\u3001\u603b\u7ed3<\/a><\/h2>\n\n\n\n

    SQL \u7684\u6838\u5fc3\u5728\u4e8e\u5bf9\u6570\u636e\u7684\u589e\u5220\u6539\u67e5\uff08CRUD\uff09\u548c\u7ed3\u6784\u7ba1\u7406\u3002\u638c\u63e1\u4e0a\u8ff0\u57fa\u672c\u8bed\u53e5\u540e\uff0c\u53ef\u4ee5\u901a\u8fc7\u7ec4\u5408\u4f7f\u7528\uff08\u5982\u5b50\u67e5\u8be2\u3001\u89c6\u56fe\u3001\u7d22\u5f15\u7b49\uff09\u5b9e\u73b0\u66f4\u590d\u6742\u7684\u529f\u80fd\u3002\u5efa\u8bae\u901a\u8fc7\u5b9e\u9645\u9879\u76ee\u7ec3\u4e60\uff08\u5982\u8bbe\u8ba1\u7535\u5546\u6570\u636e\u5e93\u3001\u5b66\u751f\u6210\u7ee9\u7ba1\u7406\u7cfb\u7edf\u7b49\uff09\u5de9\u56fa\u6280\u80fd\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"

    \u4e00\u3001\u6570\u636e\u5b9a\u4e49\u8bed\u8a00\uff08DDL\uff09 \u7528\u4e8e\u5b9a\u4e49\u548c\u7ba1\u7406\u6570\u636e\u5e93\u5bf9\u8c61\uff08\u5982\u8868\u3001\u7d22\u5f15\u3001\u89c6\u56fe\u7b49\uff09\u3002 1. CREATE\uff1a\u521b\u5efa\u6570\u636e\u5e93\u5bf9\u8c61 — \u521b\u5efa\u6570\u636e\u5e93CREATE DATABASE database_name; — \u521b\u5efa\u8868CREATE TABLE table_name (    column1 datatype constraints,    column2 datatype constraints,    …); — \u793a\u4f8b\uff1a\u521b\u5efa\u4e00\u4e2a\u5458\u5de5\u8868CREATE TABLE employees (    id INT PRIMARY KEY AUTO_INCREMENT,  — \u4e3b\u952e\uff0c\u81ea\u589e    name VARCHAR(100) NOT NULL,         — \u975e\u7a7a\u5b57\u7b26\u4e32    age INT CHECK (age >= 0),           — \u68c0\u67e5\u7ea6\u675f    department_id INT,    salary DECIMAL(10, 2) DEFAULT 0.00  — \u9ed8\u8ba4\u503c); … Continue reading SQL\uff08Structured Query Language\uff09<\/span><\/a><\/p>\n","protected":false},"author":20615,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_locale":"en_US","_original_post":"https:\/\/zd1269878.noblogs.org\/?p=219","activitypub_content_warning":"","activitypub_content_visibility":"","activitypub_max_image_attachments":4,"activitypub_interaction_policy_quote":"anyone","activitypub_status":"federated","footnotes":""},"categories":[15],"tags":[16],"class_list":["post-219","post","type-post","status-publish","format-standard","hentry","category-15","tag-16","en-US"],"_links":{"self":[{"href":"https:\/\/zd1269878.noblogs.org\/wp-json\/wp\/v2\/posts\/219","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/zd1269878.noblogs.org\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/zd1269878.noblogs.org\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/zd1269878.noblogs.org\/wp-json\/wp\/v2\/users\/20615"}],"replies":[{"embeddable":true,"href":"https:\/\/zd1269878.noblogs.org\/wp-json\/wp\/v2\/comments?post=219"}],"version-history":[{"count":2,"href":"https:\/\/zd1269878.noblogs.org\/wp-json\/wp\/v2\/posts\/219\/revisions"}],"predecessor-version":[{"id":295,"href":"https:\/\/zd1269878.noblogs.org\/wp-json\/wp\/v2\/posts\/219\/revisions\/295"}],"wp:attachment":[{"href":"https:\/\/zd1269878.noblogs.org\/wp-json\/wp\/v2\/media?parent=219"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/zd1269878.noblogs.org\/wp-json\/wp\/v2\/categories?post=219"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/zd1269878.noblogs.org\/wp-json\/wp\/v2\/tags?post=219"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}