问Teradata/SQL :如何使用teradata SQL比较连续行中的日期，并在结果上写case语句

EN

(
     SELECT
             TBL.SUBSCRIPTION
         ,   TBL.CHANNEL
         ,   TBL.SUBSCRIPTION || TBL.CHANNEL AS SUB_CHANNEL
         ,   CASE WHEN TBL.END_DT = TBL.START_DT THEN 1 ELSE 0 END AS SAME_DAY_FLAG
         ,   Dense_Rank() Over (ORDER BY SUB_CHANNEL ) AS GRP_RANK
         ,   TBL.START_DT
         ,   TBL.END_DT
         ,   PERIOD(TBL.START_DT, CASE WHEN TBL.END_DT > DATE THEN DATE ELSE TBL.END_DT + 1 END) AS COVERD_DTES
         
     FROM    <YOUR_TABLE> AS TBL
) WITH DATA
ON COMMIT PRESERVE ROWS;

/* Create a table that will contain the Merged rows with proper start and end dates combining adjacent periods*/

CREATE VOLATILE TABLE VT_TBL_MERGED_ROWS AS
(
    WITH  CTE (GRP_RANK, COVERD_DTES) AS
    (
        SELECT 
                GRP_RANK, COVERD_DTES
        FROM VT_PRE_CTE 
        
    )
    SELECT * FROM TABLE
    (    
        TD_SYSFNLIB.Td_Normalize_Overlap_Meet(NEW VARIANT_TYPE( CTE.GRP_RANK),  CTE.COVERD_DTES)
        RETURNS (GRP_RANK INT, COVERD_DTES PERIOD(DATE))
        HASH BY  GRP_RANK
        LOCAL ORDER BY GRP_RANK, COVERD_DTES
     )  AS TBL_ROWS
    
)   WITH DATA
PRIMARY INDEX (GRP_RANK);

CREATE VOLATILE TABLE VT_PRE_OUTPUT AS 
(SELECT 
                A.SUBSCRIPTION
            ,   A.CHANNEL
            ,   A.GRP_RANK
            ,   B.COVERD_DTES
            ,   Min(A.EFF_DT) AS EFF_DT
            ,   Max(A.EXP_DT) AS EXP_DT
            ,   End(B.COVERD_DTES)- Begin(B.COVERD_DTES) AS TOTAL_DAYS
        FROM    VT_PRE_CTE AS A
        JOIN    VT_TBL_MERGED_ROWS AS B
        ON      A.GRP_RANK = B.GRP_RANK 
        AND     A.COVERD_DTES OVERLAPS B.COVERD_DTES
        GROUP BY 1,2,3) 
        WITH DATA 
        PRIMARY INDEX(MTN,  EXP_DT)
        ON COMMIT PRESERVE ROWS;