sql server 查询

SQL Server是一种关系型数据库管理系统，支持SQL语言进行数据查询。以下是SQL Server查询的基本语法和示例：

1. 选择表中的若干列

SELECT column1, column2, ... FROM table_name;

2. 选择表中的若干元组

SELECT * FROM table_name WHERE condition;```

3. order by 字句

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

4. 聚集函数

SELECT COUNT(column_name) FROM table_name;
SELECT SUM(column_name) FROM table_name;
SELECT AVG(column_name) FROM table_name;
SELECT MAX(column_name) FROM table_name;
SELECT MIN(column_name) FROM table_name;

5. group by 子句

SELECT column_name1, COUNT(column_name2) FROM table_name GROUP BY column_name1;

6. 等值与非等值连接查询

SELECT * FROM table_name1 JOIN table_name2 ON condition;
SELECT * FROM table_name1 LEFT JOIN table_name2 ON condition;
SELECT * FROM table_name1 RIGHT JOIN table_name2 ON condition;

7. 带有in谓词的子查询

SELECT * FROM table_name WHERE column_name IN (SELECT column_name FROM table_name WHERE condition);

8. 带有比较运算符的子查询

SELECT * FROM table_name WHERE column_name operator (SELECT column_name FROM table_name WHERE condition);

9. 带有any或all谓词的子查询

SELECT * FROM table_name WHERE column_name operator ANY (SELECT column_name FROM table_name WHERE condition);
SELECT * FROM table_name WHERE column_name operator ALL (SELECT column_name FROM table_name WHERE condition);

10. 带有exists谓词的子查询

SELECT * FROM table_name WHERE EXISTS (SELECT column_name FROM table_name WHERE condition);