How to Combine Columns Values Into a New Column in MySQL [All Method]️
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Question: What is the best solution for this problem? Answer: This blog code can help you solve errors How to Combine Columns Values Into a New Column in MySQL. Question: What are the reasons for this code mistake and how can it be fixed? Answer: You can find a solution by following the advice in this blog.
How can we add a new column that depends on other columns in MySQL?
Suppose the current table in MySQL contains the following fields.
firstName | lastName |
---|---|
Will | Smith |
John | Doe |
We want to create a new column fullName
that contains both fields.
fullName |
---|
Will Smith |
John Doe |
This concatenation can be done through a simple CONCAT
operation.
fullName = CONCAT(firstName, ' ', lastName)
If we’re using
MySQL v8.0
, we can reference other table columns in ourDEFAULT
expression (as explained in the docs). If we’re usingMySQL v5.7
or below, we’ll have to use something similar to the method explained here.
Create the new column
First, we want to add a new nullable column.
ALTER TABLE table_name ADD COLUMN fullName VARCHAR(100);
Populate the new column
Then, we want to populate this new column with the correct values.
UPDATE table_name SET fullName = CONCAT(firstName, ' ', lastName);
Update the new column for future values
Finally, we need to ensure all new inserts and updates of the old column update the new column.
We can add a trigger for all INSERT
and UPDATE
statements on this table.
Whenever a new row is inserted or updated on table_name
, we will create or update the fullName
column with the correct, concatenated value.
CREATE TRIGGER insert_trigger
BEFORE INSERT ON table_name
FOR EACH ROW
SET new.fullName = CONCAT(firstName, ' ', lastName);
CREATE TRIGGER update_trigger
BEFORE UPDATE ON table_name
FOR EACH ROW
SET new.fullName = CONCAT(firstName, ' ', lastName);
Revise the code and make it more robust with proper test case and check an error there before implementing into a production environment.
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