Inherit values from previous records - tsql

Question

I have the following table where all fields except Value as a part of a unique index on the table. I'd like to inherit the Value from a record with Value<>NULL to the next revision record only if that record has a NULL value (See example below):
Var[n]Value fields ate varchar and there maybe 1-n number of Var[n]value fields in my table.
Source:
Document# Revision Project# config# Var1Value Var2Value
1744 1 2 1 NULL NULL
1744 2 2 1 NULL NULL
1744 3 2 1 Tit1 ABC
1744 4 2 1 Tit2 ABD
1744 5 2 1 NULL NULL
1744 6 2 1 NULL SDC
1744 7 2 1 AS
1744 8 2 1 Tit3 NULL
Needed result (notice change for revision records 5 and 6 var1value and 5,8 for var2value):
Document# Revision Project# config# Var1Value Var2Value
1744 1 2 1 NULL NULL
1744 2 2 1 NULL NULL
1744 3 2 1 Tit1 ABC
1744 4 2 1 Tit2 ABD
1744 5 2 1 Tit2 ABD
1744 6 2 1 Tit2 SDC
1744 7 2 1 AS
1744 8 2 1 Tit3 AS
Any idea how to handle it by SQL?
Please advise.
I tried the following:
declare #TableName as VarChar(32) = 'MYTABLE'
declare #SetClause as VarChar(1024)
declare #LWhereClause as VarChar(1024)
declare #RWhereClause as VarChar(1024)
-- Get the column names.
select Column_Name
into #Columns
from Information_Schema.Columns
where Table_Name = #TableName and Column_Name like 'Var%'
--select * from #Columns
-- Assemble the clauses we'll need for the UPDATE statement.
declare #ColumnName as VarChar(32)
while ( ##RowCount > 0 )
begin
select top 1 #ColumnName = Column_Name
from #Columns
order by Column_Name
set #SetClause = case when #SetClause is NULL then '' else #SetClause + ', ' end +
#ColumnName + ' = Coalesce( L.' + #ColumnName + ', R.' + #ColumnName + ' )'
set #LWhereClause = case when #LWhereClause is NULL then '' else #LWhereClause + ' or ' end +
'L.' + #ColumnName + ' is NULL'
set #RWhereClause = case when #RWhereClause is NULL then '' else #RWhereClause + ' or ' end +
'R.' + #ColumnName + ' is not NULL'
delete from #Columns
where Column_Name = #ColumnName
end
--select #SetClause, #LWhereClause, #RWhereClause
-- Put together the UPDATE statement.
declare #Update as nVarChar(max)
set #Update=''
set #Update=#Update +
'update L set ' + #SetClause + ' from ' + #TableName +
' as L inner join ' + #TableName + ' as R on R.DocId = L.DocId and R.Rev = L.Rev - 1 and R.Proj = L.Proj and R.Conf = L.Conf' +
' where ( ' + #LWhereClause + ' ) and ( ' + #RWhereClause + ' )'
-- Put together the entire loop. This needs work.
declare #Loop as nVarChar(max)
set #Loop =''
set #Loop=#Loop+
'#declare Eleanor as Int = 42;
while ( #Eleanor > 0 ) '
+ #Update + '
set #Eleanor = ##RowCount
end'
--select #Loop
-- Execute it.
exec #Loop
drop table #Columns
and I get the following error on exec loop. Why it is truncating the nvarchar string?
Msg 203, Level 16, State 2, Line 53
The name '#declare Eleanor as Int = 42;
while ( #Eleanor > 0 ) update L set variable104 = Coalesce( L.variable104, R.variable104 ), variable105 = Coalesce( L.variable105, R.variable105 ), variable106 = Coalesce( L.variable106, R.variable106 ), variable107 = Coalesce( L.variable107, R.variable107 ), variable112 = Coalesce( L.variable112, R.variable112 ), variable116 = Coalesce( L.variable116, R.variable116 ), variable119 = Coalesce( L.variable119, R.variable119 ), variable120 = Coalesce( L.variable120, R.variable120 ), variable121 = Coalesce( L.variable121, R.variable121 ), variable122 = Coalesce( L.variable122, R.variable122 ), variable124 = Co' is not a valid identifier.

Answer 1

exact duplicate of :
SQL QUERY replace NULL value in a row with a value from the previous known value
p.s:i don't have privilege to comment.so i wrote as answer.

Answer 2

EDIT: Begging your pardon, but I failed to consider the variable columns.
This query will retrieve the columns defined in YourTable:
select Column_Name from Information_Schema.Columns where Table_Name = 'YourTable'
Thereafter, you need to build a dynamic query and EXEC it. You could craft code like that shown below for each individual column, or to process all of the columns in one go.
Building the query dynamically is a somewhat tedious process. The following should get you well on your way.
declare #TableName as VarChar(32) = 'YourTable'
declare #SetClause as VarChar(1024)
declare #LWhereClause as VarChar(1024)
declare #RWhereClause as VarChar(1024)
-- Get the column names.
select Column_Name
into #Columns
from Information_Schema.Columns
where Table_Name = #TableName and Column_Name like 'Var%'
select * from #Columns
-- Assemble the clauses we'll need for the UPDATE statement.
declare #ColumnName as VarChar(32)
while ( ##RowCount > 0 )
begin
select top 1 #ColumnName = Column_Name
from #Columns
order by Column_Name
set #SetClause = case when #SetClause is NULL then '' else #SetClause + ', ' end +
#ColumnName + ' = Coalesce( L.' + #ColumnName + ', R.' + #ColumnName + ' )'
set #LWhereClause = case when #LWhereClause is NULL then '' else #LWhereClause + ' or ' end +
'L.' + #ColumnName + ' is NULL'
set #RWhereClause = case when #RWhereClause is NULL then '' else #RWhereClause + ' or ' end +
'R.' + #ColumnName + ' is not NULL'
delete from #Columns
where Column_Name = #ColumnName
end
select #SetClause, #LWhereClause, #RWhereClause
-- Put together the UPDATE statement.
declare #Update as VarChar(4096) =
'update L set ' + #SetClause + ' from ' + #TableName +
' as L inner join ' + #TableName + ' as R on R.DocId = L.DocId and R.Rev = L.Rev - 1 and R.Proj = L.Proj and R.Conf = L.Conf' +
' where ( ' + #LWhereClause + ' ) and ( ' + #RWhereClause + ' )'
-- Put together the entire loop. This needs work.
declare #Loop as VarChar(4096) =
'#declare Eleanor as Int = 42; ...' + #Update + '...'
select #Loop
-- Execute it.
exec #Loop
drop table #Columns
Here's one dreadful way that is based on revision numbers being dense:
declare #Docs as Table ( DocId Int, Rev Int, Proj Int, Conf Int, Var1 VarChar(10) Null, Var2 VarChar(10) Null )
insert into #Docs ( DocId, Rev, Proj, Conf, Var1, Var2 ) values
( 1744, 1, 2, 1, NULL, NULL ),
( 1744, 2, 2, 1, NULL, NULL ),
( 1744, 3, 2, 1, 'Tit1', 'ABC' ),
( 1744, 4, 2, 1, 'Tit2', 'ABD' ),
( 1744, 5, 2, 1, NULL, NULL ),
( 1744, 6, 2, 1, NULL, 'SDC' ),
( 1744, 7, 2, 1, '', 'AS' ), -- The example data for this row is unclear.
( 1744, 8, 2, 1, 'Tit3', NULL )
select * from #Docs
declare #Eleanor as Int = 42
while ( #Eleanor > 0 )
begin
update L
set Var1 = Coalesce( L.Var1, R.Var1 ), Var2 = Coalesce( L.Var2, R.Var2 )
from #Docs as L inner join
#Docs as R on R.DocId = L.DocId and R.Rev = L.Rev - 1 and R.Proj = L.Proj and R.Conf = L.Conf
where ( L.Var1 is NULL or L.Var2 is NULL ) and ( R.Var1 is not NULL or R.Var2 is not NULL )
set #Eleanor = ##RowCount
end
select * from #Docs