title: Case causing ORA-01790: expression must have same datatype as corresponding expression error
body: <p>I'm getting a ORA-01790: expression must have same datatype as corresponding expression error message.  Below is the sql I'm using.  Is the CASE statement causing this issue?  I'm new to sql and this is the first time I've tried using a UNION statement.  I've tried a join instead of the UNION but any join I have tried causes the prior_amt field to be blank.  Thanks for the help........</p>
  
  <pre><code>SELECT 
      pa.BUSINESS_UNIT as BUS_UNIT, 
      pa.DESCR AS DESCRIPT,
      pdr.DEPTID AS DEPTID, 
      pdr.ASSET_ID AS ASSET_NO, 
      pdr.ACCOUNT_AD AS ACCT_AD, 
      pdr.BOOK AS BOOK,
  
      MAX(CASE WHEN (pdr.FISCAL_YEAR =2014 AND pdr.ACCOUNTING_PERIOD =11) THEN  pdr.DEPR END) as CURRENT_AMT,
      MAX(CASE WHEN (pdr.FISCAL_YEAR =2104 AND pdr.ACCOUNTING_PERIOD =10) THEN pdr.DEPR  END) as PRIOR_AMT,
  
      '' AS ACCT_DE,
      '' AS JRNL_ID,
      '' AS JRNL_DT
  
      FROM PS_ASSET pa
  
      INNER JOIN PS_DEPR_RPT pdr 
      ON pa.ASSET_ID = pdr.ASSET_ID
      AND pa.BUSINESS_UNIT = pdr.BUSINESS_UNIT
  
      WHERE 
      pa.BUSINESS_UNIT='A0465'
      AND pdr.BOOK='PERFORM'
      AND ((pdr.FISCAL_YEAR=2014 AND pdr.ACCOUNTING_PERIOD=11) 
      OR (pdr.FISCAL_YEAR=2014 AND pdr.ACCOUNTING_PERIOD=10))
  
      group by
      pa.business_unit,
      pa.descr,
      pdr.deptid,
      pdr.asset_id,
      pdr.account_ad,
      pdr.book
  
  UNION ALL
  
      select
      '' as BUS_UNT,
      '' AS DESCRIPT,
      '' AS DEPTID, 
      '' AS ACCT_AD, 
      '' AS BOOK,
      '' AS CURRENT_AMT,
      '' AS PRIOR_AMT,
      pdl.asset_id AS ASSET_NO,
      pdl.account AS ACCT_DE,
      pdl.journal_id AS JRNL_ID,
      pdl.journal_date AS JRNL_DT
  
      from ps_dist_ln pdl
  
      where
      book = 'PERFORM'
      and business_unit = 'A0465'
      and fiscal_year = 2014
      and accounting_period = 11
      and distribution_type = 'DE'
  </code></pre>