MySQL - 通过在每一行连接字段来更新列

Question

I have a table as such:

ID  Name   SignUp          Unique
1   James  August2020      JamesAugust2020  
2   Tom    August2020      TomAugust2020
3   Dick   September2020   DickSeptember2020
4   Larry  June2020        LarryJune2020
5   Sam    July2020        SamJuly2020
6   John   July2020        JohnJuly2020
7   Frank  March2020       FrankMarch2020
8   Jason  August2020      JasonAugust2020

If the 'SignUp' column were to change I would like to run an update query that would concatenate and update the unique column to the new 'SignUp' date for each individual with the same 'SignUp' date.

See Example (If all 'SignUp' dates were to change from August2020 to April2020, I would like the following to happen)

ID  Name   SignUp          Unique
1   James  April2020       JamesApril2020  
2   Tom    April2020       TomApril2020
3   Dick   September2020   DickSeptember2020
4   Larry  June2020        LarryJune2020
5   Sam    July2020        SamJuly2020
6   John   July2020        JohnJuly2020
7   Frank  March2020       FrankMarch2020
8   Jason  April2020       JasonApril2020

How would I do this using an update statement in MySQL?

Answer 1

If you want unique to be the concatenation of the other two columns, then you should define it as a generated column:

alter tab t add column `unique` varchar(255) generated always as
    ( concat(name, signup) );

It is then generated when the table is queries and there is no need (or even possibility) of updating the column.

Answer 2

You can do it like this:

UPDATE tablename
SET SignUp = 'April2020',
    `Unique` = CONCAT(Name, SignUp)
WHERE SignUp = 'August2020'

In this assignment:

`Unique` = CONCAT(Name, SignUp)

MySql uses the changed value of SignUp .

See the demo .
Results:

| ID  | Name  | SignUp        | Unique            |
| --- | ----- | ------------- | ----------------- |
| 1   | James | April2020     | JamesApril2020    |
| 2   | Tom   | April2020     | TomApril2020      |
| 3   | Dick  | September2020 | DickSeptember2020 |
| 4   | Larry | June2020      | LarryJune2020     |
| 5   | Sam   | July2020      | SamJuly2020       |
| 6   | John  | July2020      | JohnJuly2020      |
| 7   | Frank | March2020     | FrankMarch2020    |
| 8   | Jason | April2020     | JasonApril2020    |

Answer 3

One option would be using REPLACE() for Unique column

UPDATE tab
   SET `SignUp` = 'April2020',
       `Unique` = REPLACE(`Unique`,'August2020', 'April2020')
 WHERE `SignUp` = 'August2020'

during the update of SignUp column

Answer 4

Table structure:

ID  Name   SignUp          Unique
1   James  August2020      JamesAugust2020  
2   Tom    August2020      TomAugust2020
3   Dick   September2020   DickSeptember2020
4   Larry  June2020        LarryJune2020
5   Sam    July2020        SamJuly2020
6   John   July2020        JohnJuly2020
7   Frank  March2020       FrankMarch2020
8   Jason  August2020      JasonAugust2020

If all 'SignUp' dates were to change from August2020 to April2020.

You can update using 2 methods:

Method 1:

UPDATE TABLE
SET SignUp='April2020',
    UNIQUE = REPLACE(UNIQUE, 'August2020', 'APRIL2020')
WHERE SignUp='August2020';

You can check detailed documentation of REPLACE

Method 2:

Or you can try another way, concat Name and Unique column

UPDATE TABLE
SET SignUp = 'April2020',
    `Unique` = CONCAT(Name, SignUp)
WHERE SignUp = 'August2020'