SQL Server : using one Select statement with 2 conditions - sql-server

Question

I have the following SQL query, and I would need it to run SELECT statement only once.
May I know what are the changes I should make?
EDIT: Need to change to use only one SELECT statement..
DECLARE
#lang varchar(2) ='en',
#hideInactiveCompany integer = 0
IF #hideInactiveCompany = 1
SELECT <all columns>
FROM Config.BusinessUnit BU
LEFT JOIN Config.Organization CO on BU.OrganizationId = CO.OrganizationId
LEFT JOIN Config.ParentBusinessUnit PBU on BU.ParentBusinessUnitId = PBU.ParentBusinessUnitId
WHERE BU.IsActive = 1 --the additional condition if #hideInactiveCompany=1
ORDER BY CASE WHEN #lang = 'cn' THEN BU.Lang END,
CASE WHEN #lang = 'en' THEN BU.Lang END DESC,
EntityName
ELSE
SELECT <all columns>
FROM Config.BusinessUnit BU
LEFT JOIN Config.Organization CO on BU.OrganizationId = CO.OrganizationId
LEFT JOIN Config.ParentBusinessUnit PBU on BU.ParentBusinessUnitId = PBU.ParentBusinessUnitId
ORDER BY CASE WHEN #lang = 'cn' THEN BU.Lang END,
CASE WHEN #lang = 'en' THEN BU.Lang END DESC,
EntityName
If #hideInactiveCompany = 1, display output with BU.IsActive =1
If #hideInactiveCompany = 0, display output without BU.IsActive
filter.

Answer 1

We can try writing the following WHERE clause:
WHERE
(hideInactiveCompany = 1 AND BU.IsActive IS NOT NULL) OR
(hideInactiveCompany IS NULL AND BU.IsActive IS NULL) OR
(hideInactiveCompany <> 1)
Note: The OP has since changed the question a few times after I answered. The latest answer appears to be this:
WHERE
(hideInactiveCompany = 1 AND BU.IsActive = 1) OR
hideInactiveCompany IS NULL OR hideInactiveCompany <> 1

Answer 2

If i do understand your requirement correctly, the entire query should have only one single SELECT clause
DECLARE
#lang varchar(2) ='en',
#hideInactiveCompany integer = 0
SELECT <all columns>
FROM Config.BusinessUnit BU
LEFT JOIN Config.Organization CO on BU.OrganizationId = CO.OrganizationId
LEFT JOIN Config.ParentBusinessUnit PBU on BU.ParentBusinessUnitId = PBU.ParentBusinessUnitId
WHERE (#hideInactiveCompany = 1 AND BU.IsActive = 1)
OR (#hideInactiveCompany <> 1)
ORDER BY CASE WHEN #lang = 'cn' THEN BU.Lang END,
CASE WHEN #lang = 'en' THEN BU.Lang END DESC,
EntityName
Explanation on WHERE
Basically there are only 2 conditions:-
Condition 1 : #hideInactiveCompany = 1 AND BU.IsActive = 1
Condition 2 : #hideInactiveCompany <> 1
Condition 1 is as what you specified. When variable #hideInactiveCompany is 1, IsActive must be 1
Condition 2 is when variable #hideInactiveCompany not equal to 1

Answer 3

You cannot do such a "conditionally build my select" in SQL. You need to write the complete select query twice, one for each branch of the if.
(SQL is generally not a "composable" langauge, you cannot freely combine the elements how you want.)
You might be able to use case and other expressions to rebuild in a single query, or doing the common part of the query into a temporary table (or table valued variable) and then only the final part twice.

Answer 4

Use IF ELSE condition:
ALTER PROCEDURE [Config].[usp_ListBusinessUnit]
#lang VARCHAR(2) = NULL,
#hideInactiveCompany INTEGER
AS
BEGIN
IF #hideInactiveCompany=1
SELECT <all columns>
FROM Config.BusinessUnit BU
LEFT JOIN Config.Organization CO ON BU.OrganizationId = CO.OrganizationId
LEFT JOIN Config.ParentBusinessUnit PBU ON BU.ParentBusinessUnitId =
PBU.ParentBusinessUnitId
WHERE BU.IsActive IS NOT NULL
ORDER BY
CASE WHEN #lang = 'cn' THEN BU.Lang END,
CASE WHEN #lang = 'en' THEN BU.Lang END DESC,
EntityName
ELSE
SELECT <all columns>
FROM Config.BusinessUnit BU
LEFT JOIN Config.Organization CO ON BU.OrganizationId = CO.OrganizationId
LEFT JOIN Config.ParentBusinessUnit PBU ON BU.ParentBusinessUnitId =
PBU.ParentBusinessUnitId
WHERE BU.IsActive IS NULL
ORDER BY
CASE WHEN #lang = 'cn' THEN BU.Lang END,
CASE WHEN #lang = 'en' THEN BU.Lang END DESC,
EntityName
END