Multiply value of field based on value range CASE? COALESCE?

Question

I have two tables. (MS SQL Server 2012)

Performance

 PortfolioID PortfolioCode  Date        MarketValue
    1         Port1         12/31/12    100000
    2         Port2         12/31/12    200000
    3         Port3         12/31/12    300000

BillingRates

RateID  FromRate        ToRate      Rate
1       1               100000      1
2       100000.01       200000      0.99
3       2000000.01      300000      0.98
4       300000.01       400000      0.97

I want to run a query that has something like a CASE statement where I say if the MarketValue of a portfolio on a particular date is between the variousvalue ranges within the tiers on the rates table than its marketvalue is multiplied by its respective rate. (The rate column represents percentage rates)

For example

Port1 falls in the RateID 1 tier and is multiplied by 1    100,000 * 1% = 1000
Port2 falls in the RateID 2 tier and is multiplied by .99  200,000 * .99% = 1980
Port3 falls in the RateID 3 tier and is multiplied by .98  300,000 * .98% = 2940

I have about 100 of these 'cases' and was thinking of doing something like this

SELECT COALESCE(
CASE WHEN condition1 THEN calculation1 ELSE NULL END,
CASE WHEN condition2 THEN calculation2 ELSE NULL END,
etc...
)

But I can't figure out the logic or how to best join the two tables to achieve this.

Answer 1

You want to join them like this:

select p.*, p.MarketValue * br.rate
from Performance p left outer join
     BillingRates br
     on p.MarketValue between br.[from] and br.[to]

This is called a non-equijoin. The performance on such joins is generally worse than on equi-joins. Having an index on [from], [to] will help.

Also, you shouldn't use SQL reserved words as column names. That is, "from" and "to" are inconvenient names.

If there might not be a match, then you might want:

select p.*, p.MarketValue * coalesce(br.rate, 1.0)

so the result is not NULL.