Conditional Where Clause

I didn’t write any post on my blog for quite long time. Today, I spend some times to write a post. Actually, this topic is saved in my draft for quite long also. :) And I received one topic from SQL Server Central which is same as my topic. We know last time that we cannot put conditional filter in where clause of T-SQL statements. But that’s not true that I find out one thing which can use conditional filter in where clause.

I'm having a request from my customer to generate dates which are based on their shifts, 135 and 246. To get all dates in a month is not difficult which I already posted in Get All Dates section. So I'm spending some times to get that conditional where clause as follow:

DECLARE @Days AS varchar(3)
SET @Days='135'

SELECT Days FROM GetAllDates
WHERE datename(dw, Days) IN (CASE WHEN SUBSTRING(@Days, 1, 1)='1' THEN 'Monday'
WHEN SUBSTRING(@Days, 1, 1)='2' THEN 'Tuesday' END,
CASE WHEN SUBSTRING(@Days, 2, 1) = '3' THEN 'Wednesday'
WHEN SUBSTRING(@Days, 2, 1) = '4' THEN 'Thursday' END,
CASE WHEN SUBSTRING(@Days, 3, 1) = '5' THEN 'Friday'
WHEN SUBSTRING(@Days, 3, 1) = '6' THEN 'Saturday' END)

The following is some another example of conditional where clause from SQL Server Central.

SELECT *
FROM Production.Product
WHERE
ProductNumber LIKE CASE
WHEN @ProductNumber IS NULL THEN '%'
ELSE @ProductNumber END
AND Color LIKE CASE
WHEN @Color IS NULL THEN '%'
ELSE @Color END

SELECT *
FROM Production.Product
WHERE ReorderPoint =
CASE
WHEN @ReorderPoint IS NULL THEN ReorderPoint
ELSE @ReorderPoint
END

Constant Column and Stock or Service Discount Setup

I didn’t update my blog for quite long time. Today, let me share some knowledge on T-SQL Programming. Last time, I posted constant table. This time, I wanna post constant fields and joining 2 tables without having any relationship.  Interesting, right? Sometimes, our customer request to generate setup data for their promotion and discount. And that time, both their services or stocks table and promotion or discount table have no relationship between them. So how we generate those data as customer requested? Let us assume stock table, STOCK, has the following format:

StockCode | Description | Price
A001 | Book | 10
A002 | Pen | 5
A003 | Pencil | 3

And the discount table, DISCOUNT, has the following format:

DiscountCode | DiscountPercentage
D010 | 10
D020 | 20
D025 | 25

Customer wants the following data:

StockCode | Price | DiscountCode | Percentage
A001 | 10 | D010 | 10
A001 | 10 | D020 | 20
A001 | 10 | D025 | 25
A002 | 5 | D010 | 10
A002 | 5 | D020 | 20
A002 | 5 | D025 | 25
A003 | 3 | D010 | 10
A004 | 3 | D020 | 20
A005 | 3 | D025 | 25

Do you notice that the data is duplicating based on DiscountCode and StockCode? Where we seen this kind of duplication? We always facing duplicate error when we join two tables wrongly, right? So now you’ll get some idea how to generate that customer request. If you still have no idea how to generate, see the following how to get those data.

At first I add constant column in each tables in query as follow:

SELECT JoinSr = 1, StockCode, Price FROM STOCK

SELECT JoinSr = 1, DiscountCode, Percentage = DiscountPercentage FROM DISCOUNT

Do you notice the column name JoinSr? That’s the constant field which will show you always one in the query result. After doing this, I’ll use our normal join statement to get the require result as follow:

SELECT S.StockCode, S.Price, D.DiscountCode, D.Percentage FROM
(SELECT JoinSr = 1, StockCode, Price FROM STOCK) S
JOIN
(SELECT JoinSr = 1, DiscountCode, Percentage = DiscountPercentage FROM DISCOUNT) D
ON S.JoinSr = D.JoinSr

Now do you notice that the error we ever facing when we join two tables is helping us to get those stock discount mapping setup.

Formatting Characters In SQL

If you want to format result values in SQL, you can use the following methods:

Let assume we have integer value variable.

DECLARE @DataValue AS int
SET @DataValue = 2

and wanna format as '00002'

There're 2 ways to format:

SELECT REPLICATE('0', 5 - LEN(@DataValue)) + CAST(@DataValue AS VARCHAR(MAX))

OR

SELECT RIGHT('00000' + CAST(@DataValue AS VARCHAR(max)), 5)

Row Data to Column Data

This is also one of my question in Experts-Exchange forum. I wanna display row data to in a columnar format. I’ve one tables which include three columns such as Sr, StartDate and EndDate. I wanna display count of Sr group by month depending on the StartDate and the resulted format is as follow:

Sr|Jan|Feb|Mar|..to..|Dec

The solution for this problem is as follow:

SELECT Sr, Jan = SUM(CASE WHEN MONTH(StartDate)=1 THEN 1 ELSE 0 END),
Feb = SUM(CASE WHEN MONTH(StartDate)=2 THEN 1 ELSE 0 END),
..
FROM Table
GROUP BY Sr

Really thanks for expert StephenCairns from Experts-Exchange for his solution which also opened my eyes on creating SQL queries later.

I also contributed some in experts exchange but my contributions are not very much so I won't post my contributions in my blog. :D

Display Different Values In Respective Columns

I haven’t updated my blog for quite long time. But today I’ve times to post some information related to the SQL query. When I prepare reports for one of the hospital in Myanmar, I’m facing some difficulties to display data and raised question in Experts-Exchange. This post is my re-collection of solutions from Experts-Exchange. And also thanks for the expert, angellll, who answer this solution for me. The problem is as follow:

I’ve one query which join 3 tables and produce different values in 2 columns.
Table A Contain (ID,SubID)
Data for Table A as example:
ID, SubID
1, 1
2, 7

Table B Contain (ID, Values)
Data for Table B as example:
ID, Values
1, 1000
2, 2500

Table C Contain (ID, SubID, Values)
Data for Table C as example:
ID, SubID, Values
1, 1, 100
1, 2, 150
1, 3, 20
2, 5, 0
2, 7, 150

I want to display as follow
ID, SubID, ID Values, SubID Values
1, 1, 1000, 100
1, 2, 0, 150
1, 3, 0, 20
2, 5, 0, 0
2, 7, 2500, 150

The solution for this problem is as follow:
SELECT a.id, a.subid, COALESCE(b.values,0) as [id values]
FROM tableA a
JOIN tableB b
ON a.ID = b.ID
RIGHT JOIN tableC c
ON c.id = a.id
AND c.subid = a.subid

Joining to the Next Sequential Row

Because of the format problem, please see this article here. Sorry for this inconvenience. ;(

Get All Dates

When we develop application, we need all the days from the month sometimes. We are thinking of the way to create StoreProcedure to generate days using temp table and cursor. But using cursor will slow down our application process and we want faster way to get all days. So we think of another way to create one table which store all the days from 1-Jan of current year to 31-Dec. That’s also not easy to maintain this table and need to insert all days every year. Actually, I’m using this method in one of my application :D. Don’t try to use this method. This is very risky to get all days and insert all days. Here is very useful query statement to generate days from the month or the given months. I got this statement from one SQL forum but I forgot from which forum and who posted it. Anyway, this statement is really helpful to me and I’m sure you’ll also. Here’s the statement:

DECLARE @FirstDay smalldatetime, @NumberOfMonths int
SELECT @FirstDay = '20080301', @NumberOfMonths = 1
;WITH Days AS (
SELECT @FirstDay as CalendarDay
UNION ALL
SELECT DATEADD(d, 1, CalendarDay) as CalendarDay
FROM Days
WHERE DATEADD(d, 1, CalendarDay) < DATEADD(m, @NumberOfMonths, @FirstDay)
)
SELECT CalendarDay FROM Days

If you set 2 to @NumberOfMonths variable, you’ll get all the days from 2 months such as Mar and Apr.