从给定的部分内容中，我们可以提炼出一系列与SQL Server数据库操作相关的高级知识点，涉及日期时间处理、查询优化、以及子查询应用等核心领域。以下是对这些知识点的详细解析：
### 1. 日期时间函数的高级用法
- **获取当前月的第一天：**
```sql
SELECT DATEADD(mm, DATEDIFF(mm, 0, GETDATE()), 0);
```
- **获取下个月的第一天减去一天（即本月最后一天）：**
```sql
SELECT DATEADD(DAY, -1, CONVERT(datetime, CONVERT(varchar(8), DATEADD(MONTH, 1, GETDATE()), 120) + '01', 120));
```
- **获取当前月的最后一天：**
```sql
SELECT DATEADD(ms, -3, DATEADD(mm, DATEDIFF(m, 0, GETDATE()) + 1, 0));
```
- **获取当前周的最后一天：**
```sql
SELECT DATEADD(wk, DATEDIFF(wk, 0, DATEADD(dd, 6 - DATEPART(day, GETDATE()), GETDATE())), 0);
```
- **获取当前年的第一天：**
```sql
SELECT DATEADD(yy, DATEDIFF(yy, 0, GETDATE()), 0);
```
- **获取下一年的第一天减去三天：**
```sql
SELECT DATEADD(ms, -3, DATEADD(yy, DATEDIFF(yy, 0, GETDATE()) + 1, 0));
```
- **获取当前年的最后一天：**
```sql
SELECT DATEADD(ms, -3, DATEADD(yy, DATEDIFF(yy, 0, GETDATE()), 0));
```
- **获取当前季度的第一天：**
```sql
SELECT DATEADD(qq, DATEDIFF(qq, 0, GETDATE()), 0);
```
- **获取当前周的第一天：**
```sql
SELECT DATEADD(wk, DATEDIFF(wk, 0, GETDATE()), 0);
```
### 2. 条件筛选查询
- **查询当月记录：**
```sql
SELECT * FROM tableName WHERE DATEPART(mm, theDate) = DATEPART(mm, GETDATE()) AND DATEPART(yy, theDate) = DATEPART(yy, GETDATE());
```
- **查询当前周的记录：**
```sql
SELECT * FROM tableName WHERE DATEPART(wk, theDate) = DATEPART(wk, GETDATE()) AND DATEPART(yy, theDate) = DATEPART(yy, GETDATE());
```
- **查询当前季度的记录：**
```sql
SELECT * FROM tableName WHERE DATEPART(qq, theDate) = DATEPART(qq, GETDATE()) AND DATEPART(yy, theDate) = DATEPART(yy, GETDATE());
```
### 3. 日期差值计算
- **计算距离下个月初的天数差：**
```sql
SELECT DATEDIFF(dd, GETDATE(), DATEADD(mm, 1, GETDATE()));
```
### 4. 子查询应用
- **查询与员工ID为141相同职位的所有员工：**
```sql
SELECT last_name, job_id FROM employees WHERE job_id = (SELECT job_id FROM employees WHERE employee_id = 141);
```
- **查询与员工ID为141相同职位且薪资高于员工ID为143的所有员工：**
```sql
SELECT last_name, job_id, salary FROM employees WHERE job_id = (SELECT job_id FROM employees WHERE employee_id = 141) AND salary > (SELECT salary FROM employees WHERE employee_id = 143);
```
- **查询每个部门薪资最低的员工：**
```sql
SELECT department_id, MIN(salary) FROM employees GROUP BY department_id HAVING MIN(salary) > (SELECT MIN(salary) FROM employees WHERE department_id = 50);
```
- **查询每个部门薪资最低的员工（注意可能存在多个）：**
```sql
SELECT employee_id, last_name FROM employees WHERE salary = (SELECT MIN(salary) FROM employees GROUP BY department_id);
```
通过以上知识点的解析，我们可以看到SQL Server提供了丰富的日期时间处理功能和强大的查询能力，特别是在处理复杂的条件筛选和子查询方面表现得尤为出色。熟练掌握这些技巧，对于提高数据检索效率和进行复杂数据分析具有重要意义。
