Update a field if another field has a certain value - mysql

Question

I am trying to update a MySQL database but only if a field has the value Approved.
If status is Approved then Date approved should update with the date.
Below is the code I am currently using but cannot get it to work. How to get it to work?
UPDATE my_table
SET `FieldValue`= IF(FieldName='status' AND FieldValue='Approved','".date('m/d/Y')."','')
WHERE `SubmissionId`=".$SubmissionId."
AND FieldName='Date Approved'
Sample Data
+--------+--------------+---------------+--------------+
| FormId | SubmissionId | FieldName | FieldValue |
+--------+--------------+---------------+--------------+
| 6 | 778 | status | Not Approved |
| 6 | 778 | Date Approved | |
+--------+--------------+---------------+--------------+

Answer 1

Use a CASE statement like below:
UPDATE my_table
SET `FieldValue` = CASE WHEN FieldName = 'status'
AND FieldValue='Approved' THEN date('m/d/Y') ELSE `FieldValue` END
WHERE `SubmissionId` = $SubmissionId;
But your query won't make sense; your FieldValue column looks like a string type column and you are trying store a date type data.

Answer 2

Something like this?
$db = JFactory::getDbo();
$query = $db->getQuery(true);
// Fields to update.
$fields = array(
$db->quoteName('FieldValue') . ' = ' . $date->toSql('m/d/Y'))
);
// Conditions for which records should be updated.
$conditions = array(
$db->quoteName('SubmissionId') . ' = SubmissionId',
$db->quoteName('FieldValue') . ' = ' . $db->quote('Approved')
);
$query->update($db->quoteName('#__my_table'))->set($fields)->where($conditions);
$db->setQuery($query);
$result = $db->execute();

Answer 3

Superficially, you should be using the raw SQL like this:
UPDATE my_table
SET FieldValue = date('m/d/Y')
WHERE SubmissionId = 778
AND FieldName = 'Date Approved'
-- AND FieldValue IS NULL -- Optional
-- AND FormId = 6 -- Optional
AND EXISTS (SELECT * FROM my_table
WHERE FieldName = 'status'
AND FieldValue = 'Approved'
AND SubmissionId = 778
-- AND FormId = 6 -- Optional
)
You might need to tart things up a little to get values embedded into the string that forms the SQL statement.
You don't mention FormID in your query; in case of doubt, you should constrain the UPDATE with the correct FormID value, twice, like you constrain the SubmissionID value twice (as shown in the comments). You might decide you only want to update the 'Date Approved' field name when it is NULL (or perhaps blank).
I note that one of the problem with this EAV design is that you lose the type-checking that a normal design gives you. You could store a date (as intended), or a pure number, or pure text, or anything else in the FieldValue column for the 'Date Approved' FieldName and there's nothing to stop that abuse happening. If you had an orthodox typed column, you could ensure that non-dates were never stored in the 'Date Approved' column.
Your UPDATE is tied to a single submission ID; so is mine. It should be possible to enhance things so that all the uninitialized 'Date Approved' columns that are approved and have not previously had the 'Date Approved' value set do in fact have it set.