I need to use the rows of one column to select another column - tsql

Question

I have as selection of Columns called Parameter(1 to 10) and I need the row select to join on the column of another table, depending on the Matrix selected. This needs to be driven by the matrix selected. The rows to columns heading is a 1-1 mapping, but the values are 1 to many. Like below:
Matrix 1 - Name, Parameter1 = First Name, Parameter2 = Last Name
Matrix 2 - Location, Parameter1 = City, Parameter2 = State, Parameter3 = Country
All the data a held in the table client detail table. The base table is over 50 columns long and there are over 100 different parameters, along with 60+ matrix possibilities.
Example - Base Table
First Name
Last Name
City
State
Country
Mary
Smith
Austin
Texas
USA
Steven
Johnson
Toronto
Ontario
Canada
Matrix
Parameter1
Parameter2
Parameter3
1
City
State
Country
2
First Name
Last Name
I need the outputs to be like :
Output A
When Matrix 1 is selected
City
State
Country
Austin
Texas
USA
Toronto
Ontario
Canada
Output B
When Matrix 2 selected
First Name
Last Name
Mary
Smith
Steven
Johnson

Answer 1

I believe you can do what you want using dynamic SQL that builds up the query and the variable conditions into a SQL string and then executes the query using sp_ExecuteSql.
Something like:
DECLARE #ConditionTemplate VARCHAR(MAX) = 'B.<ColumnName> = #Parameter<ParameterId>'
DECLARE #ConditionSeparator VARCHAR(50) = '
AND '
DECLARE #Conditions NVARCHAR(MAX) = (
SELECT STRING_AGG(REPLACE(REPLACE(
#ConditionTemplate
, '<ColumnName>', QUOTENAME(P.ColumnName))
, '<ParameterId>', CAST(P.ParameterId AS VARCHAR))
, #ConditionSeparator)
FROM Matrix M
CROSS APPLY (
VALUES
(1, M.Parameter1),
(2, M.Parameter2),
(3, M.Parameter3)
) P(ParameterId, ColumnName)
WHERE M.MatrixId = #MatrixId
AND P.ColumnName > ''
)
DECLARE #Sql NVARCHAR(MAX) = '
SELECT *
FROM BaseTable B
WHERE '
+ #Conditions
DECLARE #Params NVARCHAR(MAX) = N'#Parameter1 VARCHAR(100), #Parameter2 VARCHAR(100), #Parameter3 VARCHAR(100)'
PRINT #Sql
EXEC sp_ExecuteSql #Sql, #Params, #Parameter1, #Parameter2, #Parameter3
Most of the work is done in the #Conditions calculation. That calculation selects the proper matrix row, flatens out the data by mapping each parameter column into a numbered row, formats each into a "column = #Parameter" equality comparison, and then uses STRING_AGG() to join the conditions together. That list of conditions is then combined with the rest of the query and executed. Because the executed dynamic SQL cannot access the parameters from the calling sql, the parameters must be explicitly passed in via the sp_ExecuteSql call.
Given the following parameters:
DECLARE #MatrixId INT = 2
DECLARE #Parameter1 VARCHAR(100) = 'Steven'
DECLARE #Parameter2 VARCHAR(100) = 'Johnson'
DECLARE #Parameter3 VARCHAR(100) = NULL
The generated SQL would be as follows:
SELECT *
FROM BaseTable B
WHERE B.[First Name] = #Parameter1
AND B.[Last Name] = #Parameter2
Which will yield the following result:
First Name
Last Name
City
State
Country
Steven
Johnson
Toronto
Ontario
Canada
See this db<>fiddle.

Answer 2

I tried to repro this. Below is the SQL script.
Input Tables
1. base_table
First Name
Last Name
City
State
Country
Mary
Smith
Austin
Texas
USA
Steven
Johnson
Toronto
Ontario
Canada
2. Matrix table
Matrix
Parameter1
Parameter2
Parameter3
1
City
State
Country
2
[First Name]
[Last Name]
null
SQL script:
DECLARE #StgTable TABLE ([ColName] varchar(256), Done bit default(0));
Insert into #StgTable( [ColName] ) select concat_ws(',',parameter1,parameter2,parameter3) from matrix_table
DECLARE #SQLstmnt nvarchar(max), #colnames varchar(200);
WHILE EXISTS (SELECT 1 FROM #StgTable WHERE Done = 0) BEGIN
SELECT TOP 1 #colnames = [ColName] FROM #StgTable WHERE Done = 0;
SET #SQLstmnt = 'SELECT '+ #colnames +' FROM base_table ;';
EXECUTE sp_executesql #SQLstmnt;
UPDATE #StgTable SET Done = 1 WHERE [ColName] = #colnames;
END;
See this db<>fiddle
Output:
City
State
Country
Austin
Texas
USA
Toronto
Ontario
Canada
First Name
Last Name
Mary
Smith
Steven
Johnson