Mass update all cells in a column with a substring of it's original value

Question

I need to trim the last seven characters off of all the cells in a column.

This query returns the results that I need

SELECT test_date, SUBSTRING(test_date FROM 1 FOR CHAR_LENGTH(test_date) - 7) as test from results;

I now need to take the computed result from the substring and replace the original values.

Here's what the data looks like, if it helps.

Answer 1

Make a simple Update

CREATE TABLE Table1
    (`test_date` datetime)
;

INSERT INTO Table1
    (`test_date`)
VALUES
    ('2020-06-10 00:06:17.185449'),
    ('2020-06-10 00:11:05.943217'),
    ('2020-06-10 00:13:45.375109'),
    ('2020-06-10 00:13:45.461321'),
    ('2020-06-10 00:15:32.497548'),
    ('2020-06-10 00:15:32.544873')
;

UPDATE Table1 SET test_date = SUBSTRING(test_date FROM 1 FOR CHAR_LENGTH(test_date) - 7)

SELECT * FROm Table1

| test_date           |
| :------------------ |
| 2020-06-10 00:00:00 |
| 2020-06-10 00:00:00 |
| 2020-06-10 00:00:00 |
| 2020-06-10 00:00:00 |
| 2020-06-10 00:00:00 |
| 2020-06-10 00:00:00 |

db<>fiddle here