In MySQL, if you want to update a column with the value derived from some other column of the same table we can do so by using a SELF JOIN query and if you wish to modify the value derived from another column like maybe get a substring from the text or break the string using some delimiter, then we can use the SUBSTRING_INDEX function in the query.
For example, if you have a column A with some text and you now add a new column D in the same table, and in this new column you want to keep a part of the text stored in column A, then we can do so using the SUBSTRING_INDEX function.
If you have the following data in your table with one column postdatetime and another just postdate. And you want to pick date data from the column postdatetime and update it into the column postdate.
postdatetime postdate
2020-01-17 17:00:22 0
2020-02-12 17:00:21 0
2020-03-11 17:00:25 0
2020-04-19 17:43:56 0
2020-05-17 17:44:09 0
The column postdate should have the following data:
2012-01-17
2012-02-12
2012-03-11
2012-04-19
2012-05-17
Here we are breaking the full date time content at space.
How to Update a Column with a Substring from another Column in MySQL
If your table name is myTable with columns postdatetime and postdate, then we can run the following query:
Use a SELF JOIN, like this,
UPDATE myTable mt1, myTable mt2
SET mt1.postdate = SUBSTRING_INDEX(mt2.postdatetime," " ,1)
WHERE mt1.id = mt2.id
In the above query, the id is the primary key of the table, which is used here to pick the same row for performing the update operation.
NOTE: Update the above query as per your table and column names.
Now the above query can be a bit slow for tables that have large amounts of data.
The Better Approach:
We can do this without using SELF JOIN too, by simply running an UPDATE query which will make the query super fast.
With a big table the SELF JOIN can take a lot of time to process.
You can use UPDATE without SELF JOIN:
UPDATE myTable mt1
SET mt1.postdate = SUBSTRING_INDEX(mt1.postdatetime," " ,1);
The above query will also do the same thing but in less time.
SUBSTRING_INDEX Function:
In the SUBSTRING_INDEX function,
-
the first argument is the string,
-
the second one is the delimiter which in our case is space, you can use any character as a delimiter as per your use case,
-
the last parameter is the number of times the delimiter is to be searched. For example, we can use - as a delimiter in the above query, and from the column postdatetime, we will get the info 2020 or 2020-01 or 2020-01-17 for the first row and so on, based on the value provided for the last parameter(1, 2, or 3) of the SUBSTRING_INDEX function.
Conclusion
As data-driven applications continue to shape our digital landscape, the need for efficient data manipulation techniques becomes increasingly vital. By leveraging the power of MySQL, developers and data analysts can seamlessly update a column with substrings extracted from other columns, streamlining data transformations and enriching their databases.
In this quick tutorial, we learned how to update a column using the value from another column of the same table which is a substring of the actual value. If you have any confusion or if you are unable to run the query, feel free to share the issue with us in the comment section below.
Frequently Asked Questions(FAQs)
1. What is a substring in MySQL?
In MySQL, a substring refers to a portion of a string. It is extracted by specifying the starting position and the length of the desired substring. Substrings are commonly used to extract specific information or modify string values in a database column.
2. How can I update a column with a substring from another column in MySQL?
To update a column with a substring from another column in MySQL, you can utilize the UPDATE statement with the SUBSTRING function. By specifying the source column, the starting position, and the length, you can extract the desired substring and update the target column accordingly.
3. Can I update multiple rows with substrings using a single MySQL query?
Yes, you can update multiple rows with substrings using a single MySQL query. By incorporating appropriate conditions in the WHERE clause, you can specify the rows to be updated based on your criteria, ensuring efficient and targeted updates.
4. Can I update a column with a substring from another column and apply any transformations simultaneously?
Absolutely! MySQL provides a range of functions and operators that allow you to perform various transformations on the substring during the update operation. You can apply functions like UPPER, LOWER, CONCAT, or even mathematical operations to modify the extracted substring before updating the target column.
5. Are there any precautions I should take when updating columns with substrings in MySQL?
When updating columns with substrings in MySQL, it is crucial to ensure the correctness of the substring extraction parameters. Carefully consider the starting position, length, and any necessary adjustments based on the specific data structure. Additionally, it's always recommended to back up your data before performing any updates to avoid unintended consequences.
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