--- title: SQL Update Query localeTitle: SQL Update查询 --- ## SQL Update查询 ### Update查询可以执行什么操作 更新查询使DBA或SQL使用程序员能够使用一个命令更新许多记录。 重要安全提示！在更改之前，请始终备份您要更改的内容！ 本指南将： * 在学生表中添加一个新字段 * 测试逻辑以使用学校指定的电子邮件地址更新该字段 * 更新新字段。 这是我们开始这个过程的学生表 ```sql SELECT * FROM student; ``` ```text +-----------+------------------------+-----------+------------------+---------------------+---------------------+ | studentID | FullName | sat_score | programOfStudy | rcd_Created | rcd_Updated | +-----------+------------------------+-----------+------------------+---------------------+---------------------+ | 1 | Monique Davis | 400 | Literature | 2017-08-16 15:34:50 | 2017-08-16 15:34:50 | | 2 | Teri Gutierrez | 800 | Programming | 2017-08-16 15:34:50 | 2017-08-16 15:34:50 | | 3 | Spencer Pautier | 1000 | Programming | 2017-08-16 15:34:50 | 2017-08-16 15:34:50 | | 4 | Louis Ramsey | 1200 | Programming | 2017-08-16 15:34:50 | 2017-08-16 15:34:50 | | 5 | Alvin Greene | 1200 | Programming | 2017-08-16 15:34:50 | 2017-08-16 15:34:50 | | 6 | Sophie Freeman | 1200 | Programming | 2017-08-16 15:34:50 | 2017-08-16 15:34:50 | | 7 | Edgar Frank "Ted" Codd | 2400 | Computer Science | 2017-08-16 15:35:33 | 2017-08-16 15:35:33 | | 8 | Donald D. Chamberlin | 2400 | Computer Science | 2017-08-16 15:35:33 | 2017-08-16 15:35:33 | | 9 | Raymond F. Boyce | 2400 | Computer Science | 2017-08-16 15:35:33 | 2017-08-16 15:35:33 | +-----------+------------------------+-----------+------------------+---------------------+---------------------+ 9 rows in set (0.00 sec) ``` ### 更改表格并添加新字段 ```sql ALTER TABLE `fcc_sql_guides_database`.`student` ADD COLUMN `schoolEmailAdr` VARCHAR(125) NULL AFTER `programOfStudy`; ``` 执行alter后的student表。 ```text mysql> SELECT FullName, sat_score, programOfStudy, schoolEmailAdr FROM student; +------------------------+-----------+------------------+----------------+ | FullName | sat_score | programOfStudy | schoolEmailAdr | +------------------------+-----------+------------------+----------------+ | Monique Davis | 400 | Literature | NULL | | Teri Gutierrez | 800 | Programming | NULL | | Spencer Pautier | 1000 | Programming | NULL | | Louis Ramsey | 1200 | Programming | NULL | | Alvin Greene | 1200 | Programming | NULL | | Sophie Freeman | 1200 | Programming | NULL | | Edgar Frank "Ted" Codd | 2400 | Computer Science | NULL | | Donald D. Chamberlin | 2400 | Computer Science | NULL | | Raymond F. Boyce | 2400 | Computer Science | NULL | +------------------------+-----------+------------------+----------------+ 9 rows in set (0.00 sec) ``` ### 测试逻辑（非常重要的一步！） ```sql SELECT FullName, instr(FullName," ") AS firstSpacePosition, concat(substring(FullName,1,instr(FullName," ")-1),"@someSchool.edu") AS schoolEmail FROM student; ``` ```text +------------------------+--------------------+------------------------+ | FullName | firstSpacePosition | schoolEmail | +------------------------+--------------------+------------------------+ | Monique Davis | 8 | Monique@someSchool.edu | | Teri Gutierrez | 5 | Teri@someSchool.edu | | Spencer Pautier | 8 | Spencer@someSchool.edu | | Louis Ramsey | 6 | Louis@someSchool.edu | | Alvin Greene | 6 | Alvin@someSchool.edu | | Sophie Freeman | 7 | Sophie@someSchool.edu | | Edgar Frank "Ted" Codd | 6 | Edgar@someSchool.edu | | Donald D. Chamberlin | 7 | Donald@someSchool.edu | | Raymond F. Boyce | 8 | Raymond@someSchool.edu | +------------------------+--------------------+------------------------+ 9 rows in set (0.00 sec) ``` _关于concat（）的注释：在MySQL中，此命令用于组合字符串，而在其他SQL版本中则不然（请查看手册）。在这种用法中，它的工作方式如下：FullName字段的子字符串（但不包括第一个空格）与“@ someSchool.edu”组合在一起。在现实世界中，这将变得更加复杂，您需要确保电子邮件地址是唯一的。_ ### 进行更新 我们假装这是我们想要的，并使用以下信息更新表： ```sql UPDATE student SET schoolEmailAdr = concat(substring(FullName,1,instr(FullName," ")-1),"@someSchool.edu") WHERE schoolEmailAdr is NULL; ``` 成功！ ```text mysql> SELECT FullName, sat_score, programOfStudy, schoolEmailAdr FROM student; +------------------------+-----------+------------------+------------------------+ | FullName | sat_score | programOfStudy | schoolEmailAdr | +------------------------+-----------+------------------+------------------------+ | Monique Davis | 400 | Literature | Monique@someSchool.edu | | Teri Gutierrez | 800 | Programming | Teri@someSchool.edu | | Spencer Pautier | 1000 | Programming | Spencer@someSchool.edu | | Louis Ramsey | 1200 | Programming | Louis@someSchool.edu | | Alvin Greene | 1200 | Programming | Alvin@someSchool.edu | | Sophie Freeman | 1200 | Programming | Sophie@someSchool.edu | | Edgar Frank "Ted" Codd | 2400 | Computer Science | Edgar@someSchool.edu | | Donald D. Chamberlin | 2400 | Computer Science | Donald@someSchool.edu | | Raymond F. Boyce | 2400 | Computer Science | Raymond@someSchool.edu | +------------------------+-----------+------------------+------------------------+ 9 rows in set (0.00 sec) ``` 与所有这些SQL事物一样，它们比本入门指南中的内容更多。 我希望这至少足以让你开始。 请参阅您的数据库管理员手册，并自己尝试不同的选项。