DATETIME vs LIKE to make a dynamic search SQL - mysql

Question

I would like to dynamically search for a date in my database according to my $data input.
Dates are stored as date-times and are usually displayed as ex: "2016-05-11".
With a MySql DB my clause was:
Select * From Table WHERE ( Table.date LIKE '$data%' )
So if the user enters "20" the results will be all dates that start with 20. If the user enters "2016-05" the results will be all dates that start with 2016-05, making my search perfectly working.
When deploying over a Sql Server 2008. I realized 2 things.
1) If i use the LIKE function as Such
Select * From Table WHERE ( Table.date LIKE '%$data$%')
The function will work for a value of "2016" , but would return 0 results when a value of "2016-" is entered.
2) If i use the function DATETIME as such
Select * From Table WHERE ( DATEPART(year, Table.date) LIKE(OR)= '$data')
The function will return correct values when $data = 2016, but will return nil values when the $data = '201' for example, hence making it not dynamic.
What am i doing wrong?

Answer 1

Implicit conversion is just bad, bad, bad -- in SQL or most other programming languages.
LIKE acts on strings. If you want it to work on strings, then explicitly make sure that the parameters are strings. This is true in MySQL and SQL Server.
If you want to use LIKE on the year, then use DATENAME() rather than DATEPART():
WHERE DATENAME(year, Table.date) LIKE '$data'
However, I would encourage you to think about dates using date-based constructs, such as date ranges.

Answer 2

I just realized my stupid mistake.
I needed to add a wildcard to my LIKE clause using DATEPART as such.
Select * From Table WHERE ( DATEPART(year, Table.date) LIKE = '$data%' ) .
Works perfectly.
But i would love other suggestions to simplify splitting $data into YYYY , MM , DD and then testing each element.

Answer 3

I would strive to keep Table.date free of manipulation, so indexes are used.
Instead you can use a CASE expression to convert the search parameter to a date range by adding the missing parts:
Lower bound:
CASE LENGTH($data)
WHEN 8 THEN $data + '01'
WHEN 7 THEN $data + '-01'
WHEN 5 THEN $data + '01-01'
WHEN 4 THEN $data + '-01-01'
ELSE $data
END
Upper bound:
CASE LENGTH($data)
WHEN 8 THEN DATEADD(MONTH,$data + '01',1)
WHEN 7 THEN DATEADD(MONTH,$data + '-01',1)
WHEN 5 THEN DATEADD(YEAR,$data + '01-01')
WHEN 4 THEN DATEADD(YEAR,$data + '-01-01')
ELSE DATEADD(DAY,$data,1)
END