导入
SELECT 和 WHERE 中的子查询
学习 SQL 中嵌套查询的工作原理。
PageFlux AI 助手
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1SELECT first_name, 2 last_name, 3 salary 4FROM employees 5WHERE salary > ( 6 SELECT AVG(salary) 7 FROM employees 8);
PageFlux AI 助手
💡 选中文本后点击"AI 询问"，或 Ctrl+Enter 发送消息
1SELECT 2 first_name, 3 last_name, 4 salary, 5 (SELECT AVG(salary) FROM employees) AS company_average_salary 6FROM 7 employees;
PageFlux AI 助手
💡 选中文本后点击"AI 询问"，或 Ctrl+Enter 发送消息
1SELECT first_name, 2 last_name, 3 salary, 4 (SELECT AVG(salary) FROM employees) AS "Company Average" 5FROM employees 6WHERE salary > ( 7 SELECT AVG(salary) 8 FROM employees 9);
PageFlux AI 助手
💡 选中文本后点击"AI 询问"，或 Ctrl+Enter 发送消息
1SELECT first_name, 2 last_name, 3 salary 4FROM employees 5WHERE salary > ( 6 SELECT AVG(salary) 7 FROM employees 8);
Table
| Concept | What It Does | Example |
|---|---|---|
| Subquery | Query inside another query | (SELECT AVG(salary) FROM employees) |
| In WHERE | Filters rows by another query’s result | salary > (SELECT AVG(salary)...) |
| In SELECT | Adds a derived value as a column | (SELECT COUNT(*) FROM employees) |
| Layered logic | Lets SQL “think” in steps | “Find average → compare each value” |