MySQL - UPDATE

Update

デフォルトフォーマット:UPDATE <Table Name> SET <list of changes want to make> WHERE <condition>更新前

mysql> SELECT * FROM cats;
+--------+----------------+------------+------+
| cat_id | name           | breed      | age  |
+--------+----------------+------------+------+
|      1 | Ringo          | Tabby      |    4 |
|      2 | Cindy          | Maine Coon |   10 |
|      3 | Dumbledore     | Maine Coon |   11 |
|      4 | Egg            | Persian    |    4 |
|      5 | Misty          | Tabby      |   13 |
|      6 | George Michael | Ragdoll    |    9 |
|      7 | Jackson        | Sphynx     |    7 |
+--------+----------------+------------+------+
7 rows in set (0.00 sec)

UPDATE

mysql> UPDATE cats SET breed = 'Shorthair'
    -> WHERE breed = 'Tabby';
Query OK, 2 rows affected (0.01 sec)
Rows matched: 2  Changed: 2  Warnings: 0

Entire line is going to fined in cat table all the cats who have a breed of Tabby and change that breed to be short hair.
We have UPDATE table name then SET (And This is a list of the changes we want to make)WHERE部:Where tell特に更新する項目を選択したいです.

mysql> select * from cats;
+--------+----------------+------------+------+
| cat_id | name           | breed      | age  |
+--------+----------------+------------+------+
|      1 | Ringo          | Shorthair  |    4 |
|      2 | Cindy          | Maine Coon |   10 |
|      3 | Dumbledore     | Maine Coon |   11 |
|      4 | Egg            | Persian    |    4 |
|      5 | Misty          | Shorthair  |   13 |
|      6 | George Michael | Ragdoll    |    9 |
|      7 | Jackson        | Sphynx     |    7 |
+--------+----------------+------------+------+
7 rows in set (0.00 sec)

Another one : UPDATE cats SET age = 14 WHERE name = 'Misty';

mysql> UPDATE cats
    -> SET age = 14
    -> WHERE name = 'Misty';
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from cats;
+--------+----------------+------------+------+
| cat_id | name           | breed      | age  |
+--------+----------------+------------+------+
|      1 | Ringo          | Shorthair  |    4 |
|      2 | Cindy          | Maine Coon |   10 |
|      3 | Dumbledore     | Maine Coon |   11 |
|      4 | Egg            | Persian    |    4 |
|      5 | Misty          | Shorthair  |   14 |
|      6 | George Michael | Ragdoll    |    9 |
|      7 | Jackson        | Sphynx     |    7 |
+--------+----------------+------------+------+
7 rows in set (0.00 sec)

13歳のMistyの年齢が14歳になっているのが見えます.

A Good Rule of 👍

There is a good rule of thumb that you should follow. When you are updating something you should make sure that you're targeting the right data before you actually do the update. So basiclly run the Select the equivalent select using your WHERE query and once you make sure that returns the data you expect then update it just so that you avoid accidentally updating the wrong data.And the same holds true when we're talking about deleting which will do in just a moment but the core idea is that there is no undo button so you could update something back manually if you messed it up. But you always want to just make sure you're targeting what you mean to target before you hit enter on your update.