SQL Cheat Sheet

Complete SQL reference: SELECT, JOINs, aggregation, subqueries, and functions.

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Data Querying (SELECT)

SELECT * FROM table;Select all columns

SELECT col1, col2 FROM table;Select specific columns

SELECT DISTINCT col FROM table;Select unique values

SELECT * FROM t WHERE col = val;Filter rows with WHERE

SELECT * FROM t WHERE col LIKE '%pat%';Pattern matching with LIKE

SELECT * FROM t WHERE col IN (1, 2, 3);Filter by list of values

SELECT * FROM t WHERE col BETWEEN 10 AND 20;Filter by range

SELECT * FROM t WHERE col IS NULL;Filter NULL values

SELECT * FROM t ORDER BY col ASC;Sort results ascending

SELECT * FROM t ORDER BY col DESC;Sort results descending

SELECT * FROM t LIMIT 10;Limit number of rows returned

SELECT * FROM t LIMIT 10 OFFSET 20;Pagination — skip 20, return 10

Aggregation

SELECT COUNT(*) FROM table;Count all rows

SELECT COUNT(col) FROM table;Count non-NULL values

SELECT SUM(col) FROM table;Sum of column values

SELECT AVG(col) FROM table;Average of column values

SELECT MIN(col), MAX(col) FROM table;Minimum and maximum

SELECT col, COUNT(*) FROM t GROUP BY col;Group and count

SELECT col, COUNT(*) FROM t GROUP BY col HAVING COUNT(*) > 5;Filter groups with HAVING

JOINs

SELECT * FROM a INNER JOIN b ON a.id = b.a_id;Inner join — matching rows only

SELECT * FROM a LEFT JOIN b ON a.id = b.a_id;Left join — all rows from a

SELECT * FROM a RIGHT JOIN b ON a.id = b.a_id;Right join — all rows from b

SELECT * FROM a FULL OUTER JOIN b ON a.id = b.a_id;Full outer join — all rows

SELECT * FROM a CROSS JOIN b;Cartesian product of both tables

Data Manipulation

INSERT INTO t (c1, c2) VALUES (v1, v2);Insert a row

INSERT INTO t (c1, c2) VALUES (v1, v2), (v3, v4);Insert multiple rows

UPDATE t SET col = val WHERE id = 1;Update specific rows

DELETE FROM t WHERE id = 1;Delete specific rows

DELETE FROM t;Delete all rows (keep table)

TRUNCATE TABLE t;Delete all rows fast (DDL)

Table & Schema

CREATE TABLE t (id INT PRIMARY KEY, name VARCHAR(100));Create a table

DROP TABLE t;Delete a table

ALTER TABLE t ADD col INT;Add a column

ALTER TABLE t DROP COLUMN col;Remove a column

ALTER TABLE t RENAME TO new_name;Rename a table

CREATE INDEX idx ON t (col);Create an index

DROP INDEX idx;Remove an index

Subqueries & CTEs

SELECT * FROM t WHERE id IN (SELECT id FROM other);Subquery in WHERE

SELECT * FROM (SELECT * FROM t LIMIT 5) sub;Subquery in FROM (derived table)

WITH cte AS (SELECT * FROM t) SELECT * FROM cte;Common Table Expression (CTE)

SELECT *, ROW_NUMBER() OVER (PARTITION BY col ORDER BY date) FROM t;Window function

Useful Functions

COALESCE(col, default_val)Return first non-NULL value

NULLIF(a, b)Return NULL if a = b, else a

CASE WHEN cond THEN val ELSE other ENDConditional expression

CAST(col AS VARCHAR)Type casting

CONCAT(str1, str2)Concatenate strings

UPPER(col) / LOWER(col)Change case

TRIM(col)Remove leading/trailing whitespace

LENGTH(col)String length

SUBSTRING(col, 1, 5)Extract substring

NOW() / CURRENT_TIMESTAMPCurrent date and time

DATE_TRUNC('month', col)Truncate date to month (PostgreSQL)

關於本工具

涵蓋SELECT、INSERT、UPDATE、DELETE、JOIN、聚合函數等常用SQL語法的快速參考表。

在搜尋框輸入關鍵字，即可即時篩選相關指令。

使用方法

瀏覽各節或在搜尋框輸入關鍵字。
輸入時清單即時過濾。
將SQL片段貼入查詢編輯器或終端機。
清除搜尋以再次查看所有節。

使用情境

適合撰寫臨時查詢的開發者、學習SQL語法的學生及進行程式碼審查或資料庫遷移的工程師。

常見問題

是否涵蓋PostgreSQL、MySQL與SQLite? — 大多數語法為ANSI SQL，適用於主流資料庫。方言特有函數（如DATE_TRUNC）會有說明。
可以搜尋特定指令嗎? — 可以——在搜尋框輸入關鍵字、函數名稱或子句即可即時過濾。
清單完整嗎? — 不完整。僅涵蓋常用SQL，進階功能請參考官方文件。