Question: I have a `varchar` column where some values are in `mm/dd/yyyy` format and some are in `yyyymmdd`. 

I want to convert all `mm/dd/yyyy` dates into the `yyyymmdd` format. What is the best way to do this? Thanks

Table is `Employees` and column is `DOB`

Answer: 
try this....

```
SELECT FORMAT(CAST(DOB AS DATE),'yyyyMMdd') FROM Employees;

```
mm/dd/yyyy corresponds to U.S. standard so if you convert to date using 101 value and then to varchar using 112 for ISO date get the expected result.

```
declare @table table (date_value varchar(10))
insert into @table values ('03/30/2022'),('20220330')

select date_value
    --converted to varchar
    ,case 
        --mm/dd/yyyy pattern
        when patindex('[0,1][0-9]/[0-3][0-9]/[0-9][0-9][0-9][0-9]',date_value)>0 then convert(varchar(10),convert(date,date_value,101),112) 
        else date_value end date_value_new
    --converted to date
    ,case 
        when patindex('[0,1][0-9]/[0-3][0-9]/[0-9][0-9][0-9][0-9]',date_value)>0 then convert(date,date_value,101)
        else convert(date,date_value,112) end date_value_date
from @table

```