tsql - T-SQL Select to compute a result row on preceeding group/condition -


how achieve result using t-sql select query. given sample table :

    create table sample (a int, b int)      insert sample values (999, 10)     insert sample values (16, 11)     insert sample values (10, 12)     insert sample values (25, 13)     insert sample values (999, 20)     insert sample values (14, 12)     insert sample values (90, 45)     insert sample values (18, 34)

i'm trying achieve output:

              b            result                  ----------- -----------  -----------      999         10           10      16          11           10      10          12           10      25          13           10      999         20           20      14          12           20      90          45           20      18          34           20

the rule simple: if column 'a' has special value of 999 result row , following rows (unless value of 'a' again 999) value of column 'b'. assume first record have 999 on column 'a'.

any hint how implement, if possible, select query without using stored procedure or function?

thank you.

antónio

you need have id column 

select cn.id, cn.a      , (select top (1) b sample sample.id <= cn.id , = 999 order id desc)   sample cn  order id

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