Why is my 'WHERE' clause based on a 'DATE' failing? - sql

Question

I'm using node.js to connect to an SQL database (SQL Server 2016 specifically). My table, called transactionCounts, has the following tables and data types:
staff_id: varchar(50), date: Date, count: int;
The 'date' field is just a date, not a DateTime, for clarity. Records look like this: "2017-08-07"
I'm using the mssql package, const sql = require('mssql');
So basically, I have a function which accepts a start date and an end date and does this with them:
function(start, end) {
let ps = new sql.PreparedStatement(transactionRegisterSqlPool);
ps.input('start', sql.Date);
ps.input('end', sql.Date);
ps.prepare('SELECT staff_id, SUM(Count) TotalCount FROM [TransactionRegister].[dbo].[transactionCounts] ' +
'WHERE date >= #start AND date < #end GROUP BY staff_id', err => {
.execute({start: start, end: end}, (err, result) => {});
});
};
I've simplified the function for illustrations sake (it normally returns a promise), but here's what's going wrong:
I pass in the dates of Aug 20 midnight, and Aug 27 midnight, and what I'm expecting to get back is the sum for the dates 20,21,22,23,24,25 and 26 naturally (7 days, a week).
26th isn't being included though (definitely), and I'm not entirely sure but I'd wager that the 19th is being included. I think it's a daylight-savings issue, because these dates, when i call .toISOString(), look like 2017-08-19T23:00:00.000Z and 2017-08-26T23:00:00.000Z respectively (11pm the night prior).
I've modified my function to use strings instead of dates, and this seems to work and returns the correct Sums:
function(start, end) {
let ps = new sql.PreparedStatement(transactionRegisterSqlPool);
ps.input('start', sql.VarChar);
ps.input('end', sql.VarChar);
start = `${start.getFullYear()}/${start.getMonth() + 1}/${start.getDate()}`;
end = `${end.getFullYear()}/${end.getMonth() + 1}/${end.getDate()}`;
ps.prepare('SELECT staff_id, SUM(Count) TotalCount FROM [TransactionRegister].[dbo].[transactionCounts] ' +
'WHERE date >= #start AND date < #end GROUP BY staff_id', err => {
ps.execute({start: start, end: end}, (err, result) => {});
});
};
But it seems...wrong to take my dates and turn them into strings to work my way around this issue. What is the correct way to deal with dates between Javascript Dates and SQL Dates, so that this apparent Daylight-Savings-caused issue is avoided?

Answer 1

Your problem is that JavaScript does not have a "date" type, only "datetime", yet SQL does have a "date" type. Because of that, you will have to do the conversion.
If you wrap it in a function, it is still readable:
function toDateString(d) {
return `${d.getFullYear()}/${d.getMonth() + 1}/${d.getDate()}`;
}
ps.prepare('SELECT staff_id, SUM(Count) TotalCount FROM [TransactionRegister].[dbo].[transactionCounts] ' +
'WHERE date >= #start AND date < #end GROUP BY staff_id', err => {
ps.execute({start: toDateString(start), end: toDateString(end)}, (err, result) => {});
});