Selecting table using case clause in from clause - mysql

Question

I have 8 table that contain different specific value for computer peripheral they are glpi_device_ram, glpi_device_hdd, glpi_device_gfxcard, glpi_device_sndcard. Each table has the same designation column in each table that contain device name. i have table glpi_computer_device that contain FK_device that contain id for each 8 table above and device type column that help me decide which table(from 8 table above) should i associate with FK_device to get designation column. I have create sql syntax but not work. I need to know whether selecting table in FROM clause using CASE clause is allowed? Here is my code
SELECT CASE device_type
WHEN "1" THEN "Casing"
WHEN "2" THEN "Processor"
WHEN "3" THEN "RAM"
WHEN "4" THEN "Harddisk"
WHEN "5" THEN "Network Card"
WHEN "6" THEN "Drive"
WHEN "7" THEN "UNKNOWN"
WHEN "8" THEN "Graphic Card"
WHEN "9" THEN "Sound Card"
WHEN "10" THEN "Other device"
END AS devicetype,
CASE device_type
WHEN "1" THEN "--"
WHEN "2" THEN "Frequency"
WHEN "3" THEN "Size"
WHEN "4" THEN "Capacity"
WHEN "5" THEN "Mac Address"
WHEN "6" THEN "Memory Size"
WHEN "7" THEN "--"
WHEN "8" THEN "Memory Size"
WHEN "9" THEN "--"
WHEN "10" THEN "--"
END AS secificity_type,
specificity,
(SELECT c.designation
FROM (SELECT CASE cd.device_type
WHEN "2" THEN "glpi_device_processor"
WHEN "3" THEN "glpi_device_ram"
WHEN "4" THEN "glpi_device_hdd"
WHEN "5" THEN "glpi_device_iface"
WHEN "6" THEN "glpi_device_drive"
WHEN "8" THEN "glpi_device_gfxcard"
WHEN "9" THEN "glpi_device_sndcard"
WHEN "10" THEN "glpi_device_pci"
END
FROM glpi_computer_device cd
WHERE cd.ID = ID ) AS c
WHERE c.ID=FK_device)
FROM `glpi_computer_device`
WHERE FK_computers = 1

Answer 1

no that does not work.
you should structure this as a UNION of all 8 tables - then wrap that with another select statement to get the value.