Unable to Display Correct Date Format in 2nd Select list of UNION - teradata

Question

I have a simple query UNION ALL from two tables. I am finding that several of my columns of the second table is blank where there should be data and that the dates are shown as whole numbers (where you can discern the dates, but in YYMMDD preceded by "1"). I have shortened the query for this question to six columns to start. I have also made sure the data types are correct and even change '' to NULL and vice versa just to get errors. Here is the query:
SELECT
PRIMARY_SERVICE_DATE AS "Common Date"
,'P' AS "Claim Type"
,PRI_MEMB_ID AS "Member ID"
,PRIMARY_SERVICE_DATE AS "Primary Service Date"
,NULL AS "Admit Date"
,NULL AS "Discharge Date"
FROM MAINDB.TABLECLAIMS
WHERE
PRI_MEMB_ID IN ('99999')
UNION ALL
SELECT
ADMIT_DATE AS "Common Date"
,'' AS "Claim Type"
,CAST(MEMBER_ID AS BIGINT) AS "Member ID"
,NULL AS "Primary Service Date"
,ADMIT_DATE AS "Admit Date"
,DISCHARGE_DATE AS "Discharge Date"
FROM MAINDB.TABLESCLAIMSSUMMARY
WHERE ADMIT_DATE between '2016-01-01' and '2020-12-31'
AND CAST(MEMBER_ID AS BIGINT) IN ('99999')
This image link shows the results and how I need to display.
enter image description here

Answer 1

In Teradata, the first query in the UNION [ALL] determines the data types of the result, and in this case NULL is being considered INTEGER so the dates from the second query are implicitly CAST to INTEGERDATE form (CYYMMDD). Whenever your first query includes constant values, you should CAST to the expected result data type. (Also when data types or lengths differ you may need to explicitly CAST the result in the first query to be sure the values are returned as intended.)
SELECT
PRIMARY_SERVICE_DATE AS "Common Date"
,CAST('P' AS CHAR(1)) AS "Claim Type"
,PRI_MEMB_ID AS "Member ID"
,PRIMARY_SERVICE_DATE AS "Primary Service Date"
,CAST(NULL AS DATE) AS "Admit Date"
,CAST(NULL AS DATE) AS "Discharge Date"
FROM MAINDB.TABLECLAIMS
WHERE
PRI_MEMB_ID IN ('99999')
…
I am assuming you want the result as a DATE, despite formatting the Excel as DateTime.
If you want TIMESTAMP(0) then you should CAST all 3 dates in the first query.