122 lines
6.5 KiB
Markdown
122 lines
6.5 KiB
Markdown
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---
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title: SQL Update Query
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---
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## SQL Update Query
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### What an Update query can do
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An update query gives the DBA or SQL-using programmer the ability to update many records with one command.
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Important Safety Tip! Always have a backup copy of what you are about to change BEFORE you change it!
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This guide will:
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* add a new field to the student table
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* test the logic to update that field with a school assigned email address
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* update the new field.
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Here is the student table as we start this process
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```sql
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SELECT * FROM student;
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```
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```text
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+-----------+------------------------+-----------+------------------+---------------------+---------------------+
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| studentID | FullName | sat_score | programOfStudy | rcd_Created | rcd_Updated |
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+-----------+------------------------+-----------+------------------+---------------------+---------------------+
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| 1 | Monique Davis | 400 | Literature | 2017-08-16 15:34:50 | 2017-08-16 15:34:50 |
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| 2 | Teri Gutierrez | 800 | Programming | 2017-08-16 15:34:50 | 2017-08-16 15:34:50 |
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| 3 | Spencer Pautier | 1000 | Programming | 2017-08-16 15:34:50 | 2017-08-16 15:34:50 |
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| 4 | Louis Ramsey | 1200 | Programming | 2017-08-16 15:34:50 | 2017-08-16 15:34:50 |
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| 5 | Alvin Greene | 1200 | Programming | 2017-08-16 15:34:50 | 2017-08-16 15:34:50 |
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| 6 | Sophie Freeman | 1200 | Programming | 2017-08-16 15:34:50 | 2017-08-16 15:34:50 |
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| 7 | Edgar Frank "Ted" Codd | 2400 | Computer Science | 2017-08-16 15:35:33 | 2017-08-16 15:35:33 |
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| 8 | Donald D. Chamberlin | 2400 | Computer Science | 2017-08-16 15:35:33 | 2017-08-16 15:35:33 |
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| 9 | Raymond F. Boyce | 2400 | Computer Science | 2017-08-16 15:35:33 | 2017-08-16 15:35:33 |
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+-----------+------------------------+-----------+------------------+---------------------+---------------------+
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9 rows in set (0.00 sec)
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```
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### Alter the table and add a new field
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```sql
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ALTER TABLE `fcc_sql_guides_database`.`student`
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ADD COLUMN `schoolEmailAdr` VARCHAR(125) NULL AFTER `programOfStudy`;
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```
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The student table after the alter is executed.
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```text
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mysql> SELECT FullName, sat_score, programOfStudy, schoolEmailAdr FROM student;
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+------------------------+-----------+------------------+----------------+
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| FullName | sat_score | programOfStudy | schoolEmailAdr |
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+------------------------+-----------+------------------+----------------+
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| Monique Davis | 400 | Literature | NULL |
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| Teri Gutierrez | 800 | Programming | NULL |
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| Spencer Pautier | 1000 | Programming | NULL |
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| Louis Ramsey | 1200 | Programming | NULL |
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| Alvin Greene | 1200 | Programming | NULL |
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| Sophie Freeman | 1200 | Programming | NULL |
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| Edgar Frank "Ted" Codd | 2400 | Computer Science | NULL |
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| Donald D. Chamberlin | 2400 | Computer Science | NULL |
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| Raymond F. Boyce | 2400 | Computer Science | NULL |
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+------------------------+-----------+------------------+----------------+
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9 rows in set (0.00 sec)
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```
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### TESTING the logic (VERY important step!)
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```sql
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SELECT FullName, instr(FullName," ") AS firstSpacePosition,
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concat(substring(FullName,1,instr(FullName," ")-1),"@someSchool.edu") AS schoolEmail
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FROM student;
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```
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```text
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+------------------------+--------------------+------------------------+
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| FullName | firstSpacePosition | schoolEmail |
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+------------------------+--------------------+------------------------+
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| Monique Davis | 8 | Monique@someSchool.edu |
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| Teri Gutierrez | 5 | Teri@someSchool.edu |
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| Spencer Pautier | 8 | Spencer@someSchool.edu |
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| Louis Ramsey | 6 | Louis@someSchool.edu |
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| Alvin Greene | 6 | Alvin@someSchool.edu |
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| Sophie Freeman | 7 | Sophie@someSchool.edu |
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| Edgar Frank "Ted" Codd | 6 | Edgar@someSchool.edu |
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| Donald D. Chamberlin | 7 | Donald@someSchool.edu |
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| Raymond F. Boyce | 8 | Raymond@someSchool.edu |
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+------------------------+--------------------+------------------------+
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9 rows in set (0.00 sec)
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```
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*A note about concat(): in MySQL this command is used to combined strings, not so in other SQL versions (check your manual). In this usage it works like this: The substring of the FullName field up to but not including the first space is combined with "@someSchool.edu". In the real world this would HAVE TO be much more complex and you would need to ensure that the email address is unique.*
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### Doing the update
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We'll pretend that this is what we want and update the table with this information:
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```sql
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UPDATE student SET schoolEmailAdr = concat(substring(FullName,1,instr(FullName," ")-1),"@someSchool.edu")
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WHERE schoolEmailAdr is NULL;
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```
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Success!
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```text
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mysql> SELECT FullName, sat_score, programOfStudy, schoolEmailAdr FROM student;
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+------------------------+-----------+------------------+------------------------+
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| FullName | sat_score | programOfStudy | schoolEmailAdr |
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+------------------------+-----------+------------------+------------------------+
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| Monique Davis | 400 | Literature | Monique@someSchool.edu |
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| Teri Gutierrez | 800 | Programming | Teri@someSchool.edu |
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| Spencer Pautier | 1000 | Programming | Spencer@someSchool.edu |
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| Louis Ramsey | 1200 | Programming | Louis@someSchool.edu |
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| Alvin Greene | 1200 | Programming | Alvin@someSchool.edu |
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| Sophie Freeman | 1200 | Programming | Sophie@someSchool.edu |
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| Edgar Frank "Ted" Codd | 2400 | Computer Science | Edgar@someSchool.edu |
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| Donald D. Chamberlin | 2400 | Computer Science | Donald@someSchool.edu |
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| Raymond F. Boyce | 2400 | Computer Science | Raymond@someSchool.edu |
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+------------------------+-----------+------------------+------------------------+
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9 rows in set (0.00 sec)
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```
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As with all of these SQL things there is MUCH MORE to them than what's in this introductory guide.
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I hope this at least gives you enough to get started.
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Please see the manual for your database manager and have fun trying different options yourself.
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