Dynamic table names [closed]

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I am trying to create dynamic table names for each month.

This is how I tried it:

    declare @query varchar(max)
    declare @i date
    declare @tableid int
    declare @tblname varchar(20)

    declare @fulltablename varchar(50)

    set @tblname = 'tblLoan_'

    set @i = '07/01/2019'

    while @i <= (select max(Approval_date) from tblLoan)
    begin
    set @tableid = month(@i)
    set @fulltablename = @tblname+ cast(@tableid as varchar)


    set @query = '(select * into ['+@fulltablename+'] from  tblLoan 
    where 
    Approval_date <= '+ @i + ')'
    execute (@query)
    set @i = dateadd(month, +1, @i)

    end

I am getting this error:

Msg 402, Level 16, State 1, Line 20
The data types varchar and date are incompatible in the add operator.

After concentrating @i variable:

declare @query varchar(max)
    declare @i date
    declare @tableid int
    declare @tblname varchar(20)

declare @fulltablename varchar(50)

set @tblname = 'tblLoan_'

set @i = '07/01/2019'

while @i <= (select max(Approval_date) from tblLoan)
begin
set @tableid = month(@i)
set @fulltablename = @tblname+ cast(@tableid as varchar)


set @query = '(select * into ['+@fulltablename+'] from  tblLoan 
where 
Approval_date <= '+ convert(varchar(10),@i) + ')'
execute (@query)
set @i = dateadd(month, +1, @i)

end

Now I am getting this for every loop:

Msg 206, Level 16, State 2, Line 1
Operand type clash: datetime2 is incompatible with int

I got an exam like this in my course. I am taking a course for data analytics.

Is this a bad idea to implement in a data warehouse? If yes, why?

Answer 1

You need to convert @i to a character datatype before you can concatenate it into the @query variable.

Example with a print statement included and the exec commented out

declare @tblLoan table (Approval_date date)
insert into @tblLoan(Approval_date) values('2019-08-01')
declare @query varchar(max)
declare @i date
declare @tableid int
declare @tblname varchar(20)

declare @fulltablename varchar(50)

set @tblname = 'tblLoan_'

set @i = '07/01/2019'

while @i <= (select max(Approval_date) from @tblLoan)
begin
set @tableid = month(@i)
set @fulltablename = @tblname+ cast(@tableid as varchar)


set @query = '(select * into ['+@fulltablename+'] from  tblLoan 
where 
Approval_date <= '+ convert(varchar(10),@i) + ')'
print @query
--execute (@query)
set @i = dateadd(month, +1, @i)

end

---

(1 row affected)
(select * into [tblLoan_7] from  tblLoan 
where 
Approval_date <= 2019-07-01)
(select * into [tblLoan_8] from  tblLoan 
where 
Approval_date <= 2019-08-01)

---

To get around the operand clash error between int and datetime2, alter your dynamic code to ensure your @i date is wrapped in quotes:

Approval_date <= '''+ convert(varchar(10),@i) + ''')'

Example:

create table tblLoan (Approval_date date)
insert into tblLoan(Approval_date) values('2019-08-01')
declare @query varchar(max)
    declare @i date
    declare @tableid int
    declare @tblname varchar(20)

declare @fulltablename varchar(50)

set @tblname = 'tblLoan_'

set @i = '07/01/2019'

while @i <= (select max(Approval_date) from tblLoan)
begin
set @tableid = month(@i)
set @fulltablename = @tblname+ cast(@tableid as varchar)


set @query = '(select * into ['+@fulltablename+'] from  tblLoan 
where 
Approval_date <= '''+ convert(varchar(10),@i) + ''')'
print @query
execute (@query)
set @i = dateadd(month, +1, @i)

end