Dates and Dynamic SQL error message - sql-server

Question

Using MS SQL 2012.
I am trying to query a set of tables using dynamic SQL and I am passing through the tablename, a start date in the format of dd/MM/yyyy and an end date in the format of dd/MM/yyyy.
My Code is as follows.
#tableName nvarchar(50),
#startDate date,
#endDate date
AS
BEGIN
SET NOCOUNT ON;
DECLARE #Query varchar(max)
SET #Query = 'Select * from ''' + #tableName + ''' where Convert(date, Docdate, 103) >= ''' + CAST(#startDate AS VARCHAR(50)) + ''' and Convert(date, Docdate, 103) <= ''' + CAST(#endDate AS VARCHAR(50)) + ''
EXEC #Query
END
The Docdate field has a data type of Date and is in the format of yyyy-MM-dd.
I get the following error when I run this stored procedure.
Incorrect syntax near '/'.
What am I missing?
UPDATE
I am testing the query with the following entries for the variables and I still get the same error.
USE [TestDbs]
GO
DECLARE #return_value int
EXEC #return_value = [dbo].[getResultSet]
#tableName = Prices,
#startDate = 01/02/2016,
#endDate = 20/02/2016
SELECT 'Return Value' = #return_value
GO

Answer 1

You should use sp_executesql and pass proper date parameters to your query, and avoid the need for casting dates to strings at all:
CREATE PROCEDURE dbo.YourProcedure
#TableName SYSNAME,
#StartDate DATE,
#EndDate DATE
AS
BEGIN
DECLARE #Query NVARCHAR(MAX)
SET #Query = 'SELECT * FROM ' + QUOTENAME(#TableName) +
' WHERE Docdate >= #StartDateParam
AND Docdate <= #EndDateParam';
EXECUTE sp_executesql
#Query,
N'#startDateParam DATE, #endDateParam DATE',
#StartDateParam = #StartDate,
#EndDateParam = #EndDate;
END
I have made a couple of other minor tweaks too:
Change the datatype of #TableName from NVARCHAR(50) to SYSNAME (Synonym for `NVARCHAR(128), the maximum length of an object name)
Change the data type of #Query to NVARCHAR(MAX) since this is the type sp_executesql expects.
Wrapped #TableName with QUOTENAME to ensure any special characters do not cause an error.
If DocDate is already a date, then the explicit convert is not necessary so I have removed this.
ADDENDUM
You may also wish to add some validation to the table name:
-- CHECK TABLE NAME IS A VALID TABLE OF VIEW
IF ISNULL(OBJECT_ID(#TableName, 'U'), OBJECT_ID(#TableName, 'V')) IS NULL
BEGIN
-- HANDLE INVALID NAME
RETURN;
END
EDIT
I have changed the procedure slightly to cater for sending through a schema qualified table name
CREATE PROCEDURE dbo.getResultSet
#TableName SYSNAME,
#StartDate DATE,
#EndDate DATE
AS
BEGIN
DECLARE #Query NVARCHAR(MAX)
SET #Query = 'SELECT * FROM ' +
QUOTENAME(OBJECT_SCHEMA_NAME(OBJECT_ID(#TableName))) + '.' +
QUOTENAME(OBJECT_NAME(OBJECT_ID(#TableName))) +
' WHERE Docdate >= #StartDateParam
AND Docdate <= #EndDateParam';
EXECUTE sp_executesql
#Query,
N'#startDateParam DATE, #endDateParam DATE',
#StartDateParam = #StartDate,
#EndDateParam = #EndDate;
END
Then you would use this to execute it:
SET DATEFORMAT DMY;
DECLARE #return_value int
EXEC #return_value = [dbo].[getResultSet]
#tableName = 'dbo.Prices',
#startDate = '01/02/2016',
#endDate = '20/02/2016'
SELECT 'Return Value' = #return_value;
Or better still use a culture insensitive date format (yyyyMMdd) for your literals:
DECLARE #return_value int
EXEC #return_value = [dbo].[getResultSet]
#tableName = 'dbo.Prices',
#startDate = '20160201',
#endDate = '20160220'
SELECT 'Return Value' = #return_value;