使用带有变量的用例来确定是否必须返回计数或列列表

Question

I have a situation where on a dashboard, for pending approvals I am trying to show certain items as follows

• Item 1 [Count]
• Item 2 [Count]
• Item 3 [Count]

The [Count] shows a numeric value of items pending approval. On click of each of these items, there is an associated table where the records are being shown.

The way of deriving these counts is very complex and I wish to avoid making duplicate queries for count for example query #1 as

SELECT COUNT(*) 
FROM tableName

and then query #2 as

SELECT ColumnA, ColumnB, ColumnC 
FROM tableName

Since these queries are being read into my C# application, until now I've been doing the following

var onlyCount = true;
var subQuery = onlyCount? "COUNT(*)": "ColumnA, ColumnB, ColumnC";
var query = $"SELECT {subQuery} FROM tableName";

But with an ever-growing list of columns that needs to be managed, this makes the code look ugly. With calculated data in the select list, Case(s), IIF(s) in the statement the above-said solution is no longer a "maintainable" solution. With the select query is something as demonstrated below even possible?

DECLARE @CountOnly AS BIT = 1

SELECT 
    CASE 
        WHEN @CountOnly = 1 
            THEN COUNT(*) 
            ELSE ColumnA, ColumnB, ColumnC 
    END 
FROM 
    tableName

Have any one ever faced such a scenario? Or if you could point me in a direction where this can be handled better?

Side note: The above query is being passed into a SqlDataReader to fetch the data and show to the end user.

Answer 1

You may want to use something like this:

DECLARE @CountOnly AS BIT = 1

IF (@CountOnly = 1)
BEGIN
    SELECT ColumnA, ColumnB, ColumnC
    FROM MyTable
ELSE
    SELECT COUNT(*)
    FROM MyTable
END