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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.
We want to create a new column
fullName that contains both fields.
This concatenation can be done through a simple
fullName = CONCAT(firstName, ' ', lastName)
If we’re using
MySQL v8.0, we can reference other table columns in our
DEFAULTexpression (as explained in the docs). If we’re using
MySQL v5.7or 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
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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