How to interrogate multiple tables with different structure? - sql

Question

I am using Sql-Server 2016 in a C# application.
Let's say I have two tables:
CREATE TABLE Table_A
(
UserID NVARCHAR2(15),
FullName NVARCHAR2(25),
Available NUMBER(1),
MachineID NVARCHAR2(20),
myDate date
);
and
CREATE TABLE Table_B
(
UserID NVARCHAR2(15),
FullName NVARCHAR2(25),
Team NVARCHAR2(15),
MachineID NVARCHAR2(20),
Stuff NUMBER(2)
);
I want to perform a global select so that I will get as result data from both tables, somehow concatenated and of course, when a column does not exist in one of the tables, that column to be automatically populated with NULL, and if a column exists on both tables the results must be merged in a single column.
The first solution that pops-up is a UNION with NULL aliases for the missing columns, sure. The problem is that at runtime I will not be able to know in advance which tables are interrogated so that I could anticipate the column names. I need a more general solution.
The expected result from the two tables must look like this:
user_Table_A; fullName_Table_A; 1; machineID_Table_A; 12-JUN-18; NULL; 10;
user_Table_B; fullName_Table_B; NULL; machineID_Table_B; NULL; team_Table_B; 20;
The data for the two tables is inserted with the following commands:
INSERT INTO Table_A VALUES ('user_Table_A', 'fullName_Table_A', 1, 'machineID_Table_A', TO_DATE('12-06-2018', 'DD-MM-YYYY'));
INSERT INTO Table_B VALUES ('user_Table_B', 'fullName_Table_B', 'team_Table_B', 'machineID_Table_B', 20);

Answer 1

You can do something like this. I havent have time to completely tweak it, so there can be something the order of the columns. But perhaps it can get you started:
You also write that you use Oracle - Im not sure what you wanted, but this is in pure sql-server version.
SQL:
IF OBJECT_ID('tempdb..#temp') IS NOT NULL
/*Then it exists*/
DROP TABLE #temp;
GO
DECLARE #SQLList nvarchar(max)
DECLARE #SQLList2 nvarchar(max)
DECLARE #SQL nvarchar(max)
with table_a as (
select column_name as Table_aColumnName,ORDINAL_POSITION from INFORMATION_SCHEMA.COLUMNS
where TABLE_NAME = 'table_a'
)
,
table_b as (
select column_name as Table_bColumnName,ORDINAL_POSITION from INFORMATION_SCHEMA.COLUMNS
where TABLE_NAME = 'table_b'
)
,preresult as (
select case when Table_aColumnName IS null then 'NULL as ' + Table_bColumnName else Table_aColumnName end as Table_a_ColumnName,case when Table_bColumnName IS null then 'NULL as ' +Table_aColumnName else Table_bColumnName end as Table_b_ColumnName
,a.ORDINAL_POSITION,b.ORDINAL_POSITION as Table_b_Ordinal from table_a a full join Table_B b on a.Table_aColumnName = b.Table_bColumnName
)
select * into #temp from preresult
SET #SQLList = (
select distinct display = STUFF((select ','+table_a_columnName from #temp b order by table_b_ordinal FOR XML PATH('')),1,1,'') from #temp a
)
SET #SQLList2 = (
select distinct display = STUFF((select ','+table_b_columnName from #temp b order by Table_b_Ordinal FOR XML PATH('')),1,1,'') from #temp a
)
SET #SQL = 'select ' +#SQLList +' from dbo.Table_a union all select ' + #SQLList2 + ' from dbo.table_b'
exec(#SQL)
Result: