MySQL 按列名替换表中的值

Question

I have a MySQL table that looks like this, where pKey is a primary_AI Key.

+------+-----------+----------+----------+
| pKey | firstName | LastName | Username |
+------+-----------+----------+----------+
|    1 | John      | Brown    | jBrown   |
|    2 | Jake      | Smith    | jSmith   |
|    3 | Mary      | Laurier  | mLaurier |
+------+-----------+----------+----------+

I want to create a query where it can replace the LastName attribute when given a firstName . For example, when firstName of John is supplied, for example, I want to change the last name to Wilson .

I wrote this query to replace (or automatically create the row if not exists) the last name when supplied a first name.

REPLACE into `myTableName` (LastName, Username) VALUES ("Wilson", "jWilson") WHERE firstName = "John";

I'm expecting this query to change the record of John Brown to John Wilson and the username of jBrown to jWilson . If the row that has the first name of John doesn't exist, I also want it to create a new row with the value of John as the firstName and Wilson as the LastName as well as changing the username to jWilson .

I know that I can do this with multiple queries, such as SELECT the first name, INSERT if it does not exist, or DELETE the record and INSERT it again if it exists, but I have many records I need to insert at once and want to do this in a single query.

How can I fix this?

Answer 1

This should do it:

REPLACE into `myTableName` (Username) VALUES (CONCAT(SUBSTR(firstname,0,1),lastname))) WHERE firstName = "John";

Once it works the way you want it to, remove the WHERE

To update the existing values, use an UPDATE

UPDATE `myTableName` SET username =  LCASE(CONCAT(SUBSTR(firstname,0,1),lastname))) WHERE firstName = "John";

Answer 2

A kind of hacky way to do this since you don't want to add the unique constraint to the first_name column even though you're sure it's gonna be unique would be to get the pKey of the row where firstName = 'John', and if that doesn't exist, use the next value that's gonna be generate for pKey (since it's set as auto_increment) instead, and use on duplicate key update :

INSERT INTO table_name
 select (coalesce((select pKey from table_name where firstName = 'John'),
 (SELECT AUTO_INCREMENT
FROM information_schema.TABLES
WHERE TABLE_NAME = "table_name"))) as pKey,
 'John' as firstName,
 'Wilson' as lastName,
 'jWilson' as userName
on duplicate key update lastName = 'Wilson', userName = 'jWilson';

Fiddle