SQL 快速参考

介绍

SQL（Structured Query Language，结构化查询语言）是一种用于管理关系数据库管理系统的标准编程语言。它用于执行各种操作，如查询、更新、插入和删除数据库中的数据。本快速参考指南提供了SQL的基本语法和常用命令，旨在帮助您快速掌握SQL的基本用法。

基本语法

SELECT 语句

SELECT column1, column2, ...
FROM table_name;

INSERT 语句

INSERT INTO table_name (column1, column2, ...)
VALUES (value1, value2, ...);

UPDATE 语句

UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;

DELETE 语句

DELETE FROM table_name WHERE condition;

条件查询

WHERE 子句

SELECT column1, column2, ...
FROM table_name
WHERE condition;

AND & OR 运算符

SELECT column1, column2, ...
FROM table_name
WHERE condition1 AND condition2;

SELECT column1, column2, ...
FROM table_name
WHERE condition1 OR condition2;

NOT 运算符

SELECT column1, column2, ...
FROM table_name
WHERE NOT condition;

排序

ORDER BY 子句

SELECT column1, column2, ...
FROM table_name
ORDER BY column1, column2, ... ASC|DESC;

聚合函数

COUNT()

SELECT COUNT(column_name)
FROM table_name
WHERE condition;

SUM()

SELECT SUM(column_name)
FROM table_name
WHERE condition;

AVG()

SELECT AVG(column_name)
FROM table_name
WHERE condition;

MAX()

SELECT MAX(column_name)
FROM table_name
WHERE condition;

MIN()

SELECT MIN(column_name)
FROM table_name
WHERE condition;

分组

GROUP BY 子句

SELECT column1, SUM(column2)
FROM table_name
GROUP BY column1;

HAVING 子句

SELECT column1, SUM(column2)
FROM table_name
GROUP BY column1
HAVING condition;

连接

JOIN

SELECT columns
FROM table1
JOIN table2
ON table1.column = table2.column;

LEFT JOIN

SELECT columns
FROM table1
LEFT JOIN table2
ON table1.column = table2.column;

RIGHT JOIN

SELECT columns
FROM table1
RIGHT JOIN table2
ON table1.column = table2.column;

FULL OUTER JOIN

SELECT columns
FROM table1
FULL OUTER JOIN table2
ON table1.column = table2.column;

子查询

SELECT column1
FROM table1
WHERE column2 IN (SELECT column2 FROM table2);

结论

本快速参考指南涵盖了SQL的基本语法和常用命令。通过掌握这些基础知识，您将能够有效地查询和管理关系数据库。随着您对SQL的深入学习，您将能够运用更高级的功能和技巧来优化数据库性能和满足复杂的数据需求。