SQL 语法参考

45个条目

Basic SELECTSELECT

SELECT col1, col2 FROM table;

SELECT name, email FROM users;

ℹ Use * to select all columns (avoid in production)

SELECT with aliasSELECT

SELECT col AS alias FROM table;

SELECT first_name AS name, created_at AS joined FROM users;

SELECT DISTINCTSELECT

SELECT DISTINCT col FROM table;

SELECT DISTINCT country FROM customers;

WHERE clauseSELECT

SELECT ... FROM table WHERE condition;

SELECT * FROM orders WHERE status = 'pending' AND total > 100;

ORDER BYSELECT

SELECT ... ORDER BY col ASC|DESC;

SELECT name, price FROM products ORDER BY price DESC;

LIMIT / OFFSETSELECT

SELECT ... LIMIT n OFFSET m;

SELECT * FROM posts LIMIT 20 OFFSET 40;

ℹ SQL Server: use TOP n or FETCH NEXT

LIKE pattern matchSELECT

WHERE col LIKE 'pattern'

SELECT * FROM users WHERE email LIKE '%@gmail.com';

IN listSELECT

WHERE col IN (v1, v2, ...)

SELECT * FROM orders WHERE status IN ('pending', 'processing');

BETWEEN rangeSELECT

WHERE col BETWEEN v1 AND v2

SELECT * FROM orders WHERE total BETWEEN 100 AND 500;

IS NULL checkSELECT

WHERE col IS NULL | IS NOT NULL

SELECT * FROM users WHERE deleted_at IS NULL;

CASE expressionSELECT

CASE WHEN cond THEN val ... ELSE val END

SELECT name, CASE WHEN age >= 18 THEN 'adult' ELSE 'minor' END AS type FROM users;

COUNTAggregates

SELECT COUNT(*) | COUNT(col) FROM table;

SELECT COUNT(*) AS total, COUNT(email) AS with_email FROM users;

SUM / AVG / MIN / MAXAggregates

SELECT SUM(col), AVG(col), MIN(col), MAX(col) FROM table;

SELECT SUM(total) AS revenue, AVG(total) AS avg_order FROM orders;

GROUP BYAggregates

SELECT col, AGG(x) FROM table GROUP BY col;

SELECT country, COUNT(*) AS users FROM users GROUP BY country;

HAVINGAggregates

... GROUP BY col HAVING AGG(x) > n

SELECT country, COUNT(*) as cnt FROM users GROUP BY country HAVING COUNT(*) > 100;

GROUP BY with ORDERAggregates

... GROUP BY col ORDER BY AGG(x) DESC

SELECT status, COUNT(*) cnt FROM orders GROUP BY status ORDER BY cnt DESC;

INNER JOINJOINs

SELECT ... FROM a INNER JOIN b ON a.id = b.a_id;

SELECT u.name, o.total FROM users u INNER JOIN orders o ON u.id = o.user_id;

LEFT JOINJOINs

SELECT ... FROM a LEFT JOIN b ON a.id = b.a_id;

SELECT u.name, COUNT(o.id) FROM users u LEFT JOIN orders o ON u.id = o.user_id GROUP BY u.id;

RIGHT JOINJOINs

SELECT ... FROM a RIGHT JOIN b ON a.id = b.a_id;

SELECT o.id, u.name FROM orders o RIGHT JOIN users u ON o.user_id = u.id;

FULL OUTER JOINJOINs

SELECT ... FROM a FULL OUTER JOIN b ON condition;

SELECT a.id, b.id FROM table_a a FULL OUTER JOIN table_b b ON a.key = b.key;

ℹ Not supported in MySQL 8 — use UNION of LEFT + RIGHT JOIN

SELF JOINJOINs

SELECT ... FROM t AS a JOIN t AS b ON a.col = b.col;

SELECT e.name, m.name AS manager FROM employees e LEFT JOIN employees m ON e.manager_id = m.id;

CROSS JOINJOINs

SELECT ... FROM a CROSS JOIN b;

SELECT colors.name, sizes.label FROM colors CROSS JOIN sizes;

ℹ Returns Cartesian product — rows(a) × rows(b)

Subquery in WHERESubqueries

WHERE id IN (SELECT id FROM ...)

SELECT * FROM products WHERE category_id IN (SELECT id FROM categories WHERE active = 1);

Scalar subquerySubqueries

SELECT (SELECT COUNT(*) FROM ...) AS n

SELECT name, (SELECT COUNT(*) FROM orders WHERE user_id = u.id) AS order_count FROM users u;

EXISTSSubqueries

WHERE EXISTS (SELECT 1 FROM ...)

SELECT * FROM users u WHERE EXISTS (SELECT 1 FROM orders o WHERE o.user_id = u.id);

CTE (WITH clause)Subqueries

WITH cte AS (SELECT ...) SELECT * FROM cte;

WITH recent AS (SELECT * FROM orders WHERE created_at > NOW() - INTERVAL '7 days') SELECT user_id, COUNT(*) FROM recent GROUP BY user_id;

Recursive CTESubqueries

WITH RECURSIVE cte AS (base UNION ALL recursive) ...

WITH RECURSIVE nums(n) AS (SELECT 1 UNION ALL SELECT n+1 FROM nums WHERE n < 10) SELECT n FROM nums;

ROW_NUMBER()Window Fns

ROW_NUMBER() OVER (PARTITION BY ... ORDER BY ...)

SELECT name, ROW_NUMBER() OVER (PARTITION BY dept ORDER BY salary DESC) AS rank FROM employees;

RANK / DENSE_RANKWindow Fns

RANK() OVER (ORDER BY col DESC)

SELECT name, salary, RANK() OVER (ORDER BY salary DESC) AS pay_rank FROM employees;

ℹ RANK skips numbers on ties; DENSE_RANK does not

LAG / LEADWindow Fns

LAG(col, n) OVER (ORDER BY ...)

SELECT date, revenue, LAG(revenue,1) OVER (ORDER BY date) AS prev_revenue FROM daily_sales;

SUM() OVER (running total)Window Fns

SUM(col) OVER (ORDER BY col ROWS UNBOUNDED PRECEDING)

SELECT date, amount, SUM(amount) OVER (ORDER BY date) AS running_total FROM transactions;

NTILE(n)Window Fns

NTILE(n) OVER (ORDER BY col)

SELECT name, salary, NTILE(4) OVER (ORDER BY salary) AS quartile FROM employees;

INSERT single rowDML

INSERT INTO table (col1, col2) VALUES (v1, v2);

INSERT INTO users (name, email) VALUES ('Alice', '[email protected]');

INSERT multiple rowsDML

INSERT INTO table (cols) VALUES (r1), (r2), ...;

INSERT INTO tags (name) VALUES ('sql'), ('database'), ('tutorial');

INSERT … SELECTDML

INSERT INTO t1 (cols) SELECT cols FROM t2;

INSERT INTO archive SELECT * FROM orders WHERE created_at < '2023-01-01';

UPDATEDML

UPDATE table SET col = val WHERE condition;

UPDATE users SET status = 'inactive', updated_at = NOW() WHERE last_login < NOW() - INTERVAL '90 days';

DELETEDML

DELETE FROM table WHERE condition;

DELETE FROM sessions WHERE expires_at < NOW();

ℹ Always include WHERE — omitting it deletes all rows

UPSERT (ON CONFLICT)DML

INSERT … ON CONFLICT (col) DO UPDATE SET …

INSERT INTO settings (key, value) VALUES ('theme', 'dark') ON CONFLICT (key) DO UPDATE SET value = EXCLUDED.value;

ℹ PostgreSQL syntax. MySQL uses ON DUPLICATE KEY UPDATE.

TRUNCATEDML

TRUNCATE TABLE table;

TRUNCATE TABLE temp_imports;

ℹ Faster than DELETE; resets auto-increment; cannot be rolled back in some DBs

CREATE TABLEDDL

CREATE TABLE name (col type constraints, ...);

CREATE TABLE users (id SERIAL PRIMARY KEY, email VARCHAR(255) UNIQUE NOT NULL, created_at TIMESTAMPTZ DEFAULT NOW());

ALTER TABLE ADD COLUMNDDL

ALTER TABLE t ADD COLUMN col type;

ALTER TABLE users ADD COLUMN phone VARCHAR(20);

ALTER TABLE RENAMEDDL

ALTER TABLE t RENAME COLUMN old TO new;

ALTER TABLE users RENAME COLUMN username TO display_name;

CREATE INDEXDDL

CREATE INDEX name ON table (col);

CREATE INDEX idx_users_email ON users (email);
CREATE UNIQUE INDEX idx_users_email_unique ON users (email);

DROP TABLEDDL

DROP TABLE [IF EXISTS] table;

DROP TABLE IF EXISTS temp_staging;

FOREIGN KEYDDL

REFERENCES other_table(col) ON DELETE action

CREATE TABLE orders (id SERIAL PRIMARY KEY, user_id INT REFERENCES users(id) ON DELETE CASCADE);

SQL子句执行顺序

FROM→

JOIN→

WHERE→

GROUP BY→

HAVING→

SELECT→

DISTINCT→

ORDER BY→

LIMIT

这是逻辑的处理顺序。WHERE在SELECT之前运行，因此无法在以下位置引用SELECT别名 WHERE子句 — 改用CTE或子查询。HAVING可以过滤 GROUP BY聚合上。

NULL处理规则

表达式	结果	注意事项
NULL = NULL	FALSE / UNKNOWN	Use IS NULL instead
NULL != NULL	UNKNOWN	Any comparison with NULL is UNKNOWN
NULL + 5	NULL	Arithmetic on NULL propagates NULL
COALESCE(NULL, 'x')	'x'	Returns first non-NULL value
NULLIF(a, a)	NULL	Returns NULL if both args are equal
COUNT(*)	Counts all rows	COUNT(col) skips NULLs

SQL快速参考常见问题

SQL子句的执行顺序是什么？

SQL子句按以下逻辑顺序执行：FROM → JOIN → WHERE → GROUP BY → HAVING → SELECT → DISTINCT → ORDER BY → LIMIT/OFFSET。这很重要，因为WHERE不能引用SELECT别名，但HAVING可以引用GROUP BY列。

INNER JOIN和LEFT JOIN有什么区别？

INNER JOIN仅返回两个表中连接条件匹配的行。LEFT JOIN（LEFT OUTER JOIN）返回左表中的所有行，对不匹配的右表列返回NULL。当您需要左表中的所有记录，无论右侧是否有匹配时，使用LEFT JOIN。

SQL中的窗口函数是什么？

窗口函数在与当前行相关的一组行中计算值，而不像GROUP BY聚合那样将其折叠为单行。常见的窗口函数：ROW_NUMBER(), RANK(), DENSE_RANK(), LAG(), LEAD(), SUM() OVER(), AVG() OVER()。它们使用OVER()子句来定义窗口。

什么是CTE（公共表表达式）？

CTE是在SELECT, INSERT, UPDATE或DELETE语句之前使用WITH关键字定义的命名临时结果集。CTE比嵌套子查询更易读，还可以是递归的（WITH RECURSIVE），用于组织架构或类别树等层次数据。

Docker 速查表 — 命令参考 Docker Compose 转换器 Git 速查表 — Git 命令参考 Bash 速查表 — 命令参考 & 示例 Chmod 计算器 — Unix 文件权限计算器 Cron 表达式生成器 — 计划任务生成器

NULL处理规则

表达式	结果	注意事项
NULL = NULL	FALSE / UNKNOWN	Use IS NULL instead
NULL != NULL	UNKNOWN	Any comparison with NULL is UNKNOWN
NULL + 5	NULL	Arithmetic on NULL propagates NULL
COALESCE(NULL, 'x')	'x'	Returns first non-NULL value
NULLIF(a, a)	NULL	Returns NULL if both args are equal
COUNT(*)	Counts all rows	COUNT(col) skips NULLs

SQL 语法 参考

SQL子句执行顺序

NULL处理规则

SQL快速参考常见问题

SQL子句的执行顺序是什么？

INNER JOIN和LEFT JOIN有什么区别？

SQL中的窗口函数是什么？

什么是CTE（公共表表达式）？

相关工具

SQL 语法 参考

SQL子句执行顺序

NULL处理规则

SQL快速参考常见问题

SQL子句的执行顺序是什么？

INNER JOIN和LEFT JOIN有什么区别？

SQL中的窗口函数是什么？

什么是CTE（公共表表达式）？

相关工具

SQL 语法参考

SQL 语法参考