SQL Server Update语句

在本教程中，将学习如何使用SQL Server UPDATE语句更改表中的现有数据。

要修改表中的现有数据，请使用以下UPDATE语句语法：

UPDATE table_name
SET c1 = v1, c2 = v2, ... cn = vn
[WHERE condition]

在上面语法中，

• 首先，指定要从中更新数据的表的名称。
• 其次，指定要更新的列c1，c2，...，cn和值v1，v2，... vn的列表。
• 第三，在WHERE子句中指定条件以选择更新的行。WHERE子句是可选的。 如果不指定WHERE子句，则表中的所有行都将更新。

SQL Server UPDATE示例

首先，创建一个名为taxes的新表。

CREATE TABLE sales.taxes (
    tax_id INT PRIMARY KEY IDENTITY (1, 1),
    state VARCHAR (50) NOT NULL UNIQUE,
    state_tax_rate DEC (3, 2),
    avg_local_tax_rate DEC (3, 2),
    combined_rate AS state_tax_rate + avg_local_tax_rate,
    max_local_tax_rate DEC (3, 2),
    updated_at datetime
);

其次，执行以下语句将数据插入taxes表：

INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Alabama',0.04,0.05,0.07);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Alaska',0,0.01,0.07);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Arizona',0.05,0.02,0.05);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Arkansas',0.06,0.02,0.05);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('California',0.07,0.01,0.02);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Colorado',0.02,0.04,0.08);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Connecticut',0.06,0,0);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Delaware',0,0,0);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Florida',0.06,0,0.02);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Georgia',0.04,0.03,0.04);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Hawaii',0.04,0,0);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Idaho',0.06,0,0.03);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Illinois',0.06,0.02,0.04);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Indiana',0.07,0,0);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Iowa',0.06,0,0.01);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Kansas',0.06,0.02,0.04);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Kentucky',0.06,0,0);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Louisiana',0.05,0.04,0.07);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Maine',0.05,0,0);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Maryland',0.06,0,0);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Massachusetts',0.06,0,0);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Michigan',0.06,0,0);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Minnesota',0.06,0,0.01);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Mississippi',0.07,0,0.01);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Missouri',0.04,0.03,0.05);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Montana',0,0,0);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Nebraska',0.05,0.01,0.02);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Nevada',0.06,0.01,0.01);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('New Hampshire',0,0,0);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('New Jersey',0.06,0,0);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('New Mexico',0.05,0.02,0.03);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('New York',0.04,0.04,0.04);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('North Carolina',0.04,0.02,0.02);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('North Dakota',0.05,0.01,0.03);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Ohio',0.05,0.01,0.02);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Oklahoma',0.04,0.04,0.06);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Oregon',0,0,0);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Pennsylvania',0.06,0,0.02);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Rhode Island',0.07,0,0);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('South Carolina',0.06,0.01,0.02);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('South Dakota',0.04,0.01,0.04);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Tennessee',0.07,0.02,0.02);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Texas',0.06,0.01,0.02);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Utah',0.05,0,0.02);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Vermont',0.06,0,0.01);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Virginia',0.05,0,0);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Washington',0.06,0.02,0.03);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('West Virginia',0.06,0,0.01);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Wisconsin',0.05,0,0.01);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('Wyoming',0.04,0.01,0.02);
INSERT INTO sales.taxes(state,state_tax_rate,avg_local_tax_rate,max_local_tax_rate) VALUES('D.C.',0.05,0,0);

1. 更新所有行示例中的单个列

以下语句更新taxs表中所有行的单个列：

UPDATE sales.taxes
SET updated_at = GETDATE();

在此示例中，语句将updated_at列中的值更改为GETDATE()函数返回的系统日期时间。

SQL Server发出以下消息：

(51 rows affected)

这表示有51行记录已成功更新。

下面通过以下查询来验证更新结果：

SELECT
    *
FROM
    sales.taxes;

从输出中可以清楚地看到，updated_at列已使用当前日期值进行更新。

2. 更新多列示例

对于最高当地税率为1%的州，以下语句将最高当地税率提高2%，以及平均税率提高1%。

UPDATE sales.taxes
SET max_local_tax_rate += 0.02,
    avg_local_tax_rate += 0.01
WHERE
    max_local_tax_rate = 0.01;

以下是SQL Server返回的消息：

(7 rows affected)

这意味着7个州的税收已经更新。

在本教程中，学习了如何使用SQL Server UPDATE语句来修改表中的现有数据。