Use PivotTable with Left Outer Join - mysql

Question

I'm fairly new to MySQL.
Put simply, I want to turn each "meta_key" value into a column of the resulting table.
I've got two tables with the following schema:
CREATE TABLE `frmt_form_entry` (
`entry_id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`entry_type` varchar(191) COLLATE utf8mb4_unicode_520_ci NOT NULL,
`form_id` bigint(20) unsigned NOT NULL,
`is_spam` tinyint(1) NOT NULL DEFAULT '0',
`date_created` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
PRIMARY KEY (`entry_id`),
KEY `entry_is_spam` (`is_spam`),
KEY `entry_type` (`entry_type`),
KEY `entry_form_id` (`form_id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_520_ci;
CREATE TABLE `frmt_form_entry_meta` (
`meta_id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`entry_id` bigint(20) unsigned NOT NULL,
`meta_key` varchar(191) COLLATE utf8mb4_unicode_520_ci DEFAULT NULL,
`meta_value` longtext COLLATE utf8mb4_unicode_520_ci,
`date_created` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
`date_updated` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
PRIMARY KEY (`meta_id`),
KEY `meta_key` (`meta_key`),
KEY `meta_entry_id` (`entry_id`),
KEY `meta_key_object` (`entry_id`,`meta_key`)
) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_520_ci;
There exist multiple "meta entries" per "form entry":
INSERT INTO `frmt_form_entry` (`entry_id`, `entry_type`, `form_id`, `is_spam`, `date_created`)
VALUES
(1, 'custom-forms', 3744, 0, '2020-08-14 13:00:32');
INSERT INTO `frmt_form_entry_meta` (`meta_id`, `entry_id`, `meta_key`, `meta_value`, `date_created`, `date_updated`)
VALUES
(1, 1, 'text-7', 'Foreign Legal Form', '2020-08-14 13:00:32', '0000-00-00 00:00:00'),
(2, 1, 'name-1', 'Test Name', '2020-08-14 13:00:32', '0000-00-00 00:00:00'),
(3, 1, 'address-1', 'a:6:{s:7:\"country\";s:0:\"\";s:4:\"city\";s:0:\"\";s:5:\"state\";s:0:\"\";s:3:\"zip\";s:0:\"\";s:14:\"street_address\";s:0:\"\";s:12:\"address_line\";s:0:\"\";}', '2020-08-14 13:00:32', '0000-00-00 00:00:00'),
(4, 1, 'address-2', 'a:6:{s:7:\"country\";s:0:\"\";s:4:\"city\";s:0:\"\";s:5:\"state\";s:0:\"\";s:3:\"zip\";s:0:\"\";s:14:\"street_address\";s:0:\"\";s:12:\"address_line\";s:0:\"\";}', '2020-08-14 13:00:32', '0000-00-00 00:00:00'),
(5, 1, 'address-3', 'a:6:{s:7:\"country\";s:0:\"\";s:4:\"city\";s:0:\"\";s:5:\"state\";s:0:\"\";s:3:\"zip\";s:0:\"\";s:14:\"street_address\";s:0:\"\";s:12:\"address_line\";s:0:\"\";}', '2020-08-14 13:00:32', '0000-00-00 00:00:00'),
(6, 1, '_forminator_user_ip', '8.8.8.8', '2020-08-14 13:00:32', '0000-00-00 00:00:00'),
(7, 1, 'stripe-1', 'a:6:{s:4:\"mode\";s:4:\"test\";s:6:\"status\";s:7:\"success\";s:6:\"amount\";s:2:\"0\";s:8:\"currency\";s:3:\"\";s:14:\"transaction_id\";s:27:\"\";s:16:\"transaction_link\";s:70:\"\";}', '2020-08-14 13:00:32', '0000-00-00 00:00:00');
I'd like to create a Pivot Table with the same number of rows as there are rows in the frmt_form_entry table (1 in this case).
I want each meta key to be a column name of that pivot table. Since each meta key can only exist once per entry_id, I won't need to concatenate the meta values of multiple fields for the same meta key.
This is the expected output:
entry_id entry_type form_id is_spam date_created text-7 name-1 address-1 address-2 address-3. _forminator_user_ip stripe-1
1 custom-forms 3744 0 2020-08-14 13:00:32 Foreign Legal Form Test Name [...]
What I've tried so far:
SELECT entries.*,
CASE WHEN meta.`meta_key`='stripe-1'
THEN meta.`meta_value`
ELSE NULL
END
AS stripe,
CASE WHEN meta.`meta_key`='text-7'
THEN meta.`meta_value`
ELSE NULL
END
AS text7,
CASE WHEN meta.`meta_key`='_forminator_user_ip'
THEN meta.`meta_value`
ELSE NULL
END
AS user_ip,
CASE WHEN meta.`meta_key`='address-1'
THEN meta.`meta_value`
ELSE NULL
END
AS address1,
CASE WHEN meta.`meta_key`='address-2'
THEN meta.`meta_value`
ELSE NULL
END
AS address2,
CASE WHEN meta.`meta_key`='address-3'
THEN meta.`meta_value`
ELSE NULL
END
AS address3,
CASE WHEN meta.`meta_key`='name-1'
THEN meta.`meta_value`
ELSE NULL
END
AS name1
FROM frmt_form_entry entries
LEFT OUTER JOIN frmt_form_entry_meta meta
ON entries.entry_id = meta.entry_id
However, this feels wrong and messy and it doesn't give the expected result (it creates one entry per meta value).
Is there an easy, better way to turn each "meta_key" value into a column of the resulting table?

Answer 1

Sorry, but I am going to be rather blunt. "Entry-Attribute-Value" is a great schema pattern for textbooks, but not for the real world.
EAV is especially inappropriate for columns that exist for all the items. If "every" location has an address, city, etc, then make them columns. Simpler. More efficient. (In the case of address_1 and an optional address_2, use NULL to indicate optionality.) Do you ever need the parts of an address for searching or filtering? If not, then simply have a single column for the whole "address".
Reserve "meta" for attributes that are usually not present. As a separate discussion we can discuss the benefits/drawbacks of using a single JSON column for such. Or how to do searching with FULLTEXT.
Do you really need the date_created and date_updated?
The 4 indexes you have on the meta table are quite inefficient. See this for tips on improving it: http://mysql.rjweb.org/doc.php/index_cookbook_mysql#speeding_up_wp_postmeta