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在 SQL Server 中进行数据查询通常使用 Transact-SQL (T-SQL),这是 SQL Server 的扩展版本。以下是一些基本的 SQL Server 数据查询操作:
选择所有数据:
SELECT * FROM TableName;
选择特定列:
sql
SELECT Column1, Column2 FROM TableName;
使用 WHERE 子句过滤数据:
SELECT * FROM TableName WHERE Condition;
示例:
SELECT * FROM Employees WHERE Salary > 50000;
使用 ORDER BY 子句排序数据:
SELECT * FROM TableName ORDER BY Column1 [ASC|DESC];
示例:
SELECT * FROM Employees ORDER BY Salary DESC;
使用聚合函数统计数据:
SELECT COUNT(Column1), AVG(Column2), SUM(Column3) FROM TableName WHERE Condition;
示例:
sql
SELECT COUNT(EmployeeID), AVG(Salary), SUM(Salary) FROM Employees WHERE DepartmentID = 1;
使用 GROUP BY 子句分组数据:
SELECT Column1, COUNT(Column2) FROM TableName GROUP BY Column1;
示例:
SELECT DepartmentID, COUNT(EmployeeID) FROM Employees GROUP BY DepartmentID;
使用 INNER JOIN 连接表:
SELECT * FROM Table1 INNER JOIN Table2 ON Table1.Column = Table2.Column;
示例:
SELECT Employees.EmployeeID, Employees.EmployeeName, Departments.DepartmentName
FROM Employees
INNER JOIN Departments ON Employees.DepartmentID = Departments.DepartmentID;
使用子查询嵌套在 SELECT 语句中:
SELECT Column1, (SELECT MAX(Column2) FROM Table2 WHERE Condition) AS MaxValue FROM Table1;
示例:
SELECT EmployeeName, (SELECT MAX(Salary) FROM Employees) AS MaxSalary FROM Employees;
这只是 SQL Server 数据查询的一小部分,实际应用中可能涉及更复杂的查询操作。T-SQL 支持丰富的语法和功能,允许开发者根据具体需求编写复杂的查询语句。在实践中,了解索引的使用、优化查询计划等也是提高查询性能的关键。
该博文为原创文章,未经博主同意不得转载。本文章博客地址:https://blog.csdn.net/weixin_39145520/article/details/134742484
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