MYSQL UNION JOIN SUM（amount）输出两个结果而不是一个

Question

I have this below:

SELECT a.* FROM ( SELECT
      asset_liability_income_expenditure_tbl.a_l_code,
      SUM(mainaccount_a_2017.amount), mainaccount_a_2017.dr_cr_action 
      FROM `mainaccount_a_2017` LEFT JOIN chart_of_account 
      ON (
         chart_of_account.joint_account_numbers =
         mainaccount_a_2017.joint_account_number
       ) 
      LEFT JOIN asset_liability_income_expenditure_tbl 
      ON (
         asset_liability_income_expenditure_tbl.a_l_code =
         chart_of_account.account_type
      ) 
WHERE asset_liability_income_expenditure_tbl.a_l_code = 'FA' 
      AND mainaccount_a_2017.dr_cr_action = 'DR' UNION 
SELECT asset_liability_income_expenditure_tbl.a_l_code,
SUM(mainaccount_b_2017.amount), 
mainaccount_b_2017.dr_cr_action 
FROM `mainaccount_b_2017` 
LEFT JOIN chart_of_account ON (
          chart_of_account.joint_account_numbers = 
          mainaccount_b_2017.joint_account_number
      ) 
LEFT JOIN asset_liability_income_expenditure_tbl ON ( 
           asset_liability_income_expenditure_tbl.a_l_code =
           chart_of_account.account_type
      ) 
WHERE asset_liability_income_expenditure_tbl.a_l_code = 'FA' 
      AND mainaccount_b_2017.dr_cr_action = 'DR' 
) AS a

it works fine, but displays either one empty row at the top and the sum below or vis-a-vis. I tried LIMIT 1, but the problem is when the SUM(amount) outputs in row 2, i cannot fetch and if I don't apply any limit, it only fetches result whose SUM(amount) outputs in row 1. I don't know what am missing. Please kindly assist. Thanks.

Answer 1

I figured it out. I had to flip something. Results below:

SELECT SUM(a) FROM
(
  SELECT SUM(mainaccount_a_2017.amount) 
  AS a FROM `mainaccount_a_2017`
  LEFT JOIN chart_of_account ON (chart_of_account.joint_account_numbers = mainaccount_a_2017.joint_account_number)

  LEFT JOIN asset_liability_income_expenditure_tbl ON (asset_liability_income_expenditure_tbl.a_l_code = chart_of_account.account_type)

  WHERE asset_liability_income_expenditure_tbl.a_l_code = 'FA' 
  AND mainaccount_a_2017.dr_cr_action = 'DR'

  UNION ALL

  SELECT SUM(mainaccount_b_2017.amount) 
  AS a FROM `mainaccount_b_2017`
  LEFT JOIN chart_of_account ON (chart_of_account.joint_account_numbers = mainaccount_b_2017.joint_account_number)

  LEFT JOIN asset_liability_income_expenditure_tbl ON (asset_liability_income_expenditure_tbl.a_l_code = chart_of_account.account_type)

  WHERE asset_liability_income_expenditure_tbl.a_l_code = 'FA' AND mainaccount_b_2017.dr_cr_action = 'DR'
) a