How to compare data from multiple databases - sql

Question

I'm trying to compare some data from different multiple databases, as I have illustrate my current case, I have there databases, database 1 is the main, and time to time database 2 and database 3 are updated from database 1. I have some difficulties to get the final result which return the data from database 1 and two columns column show the availability in database 2 as Yes or No, and the same with second extra column that will indicate the data availability on the database 3 with Yes or NO.
SELECT *
FROM (
Select ID as db1_ID,
First_name as db1_First_name,
Last_name as db1_Last_name,
Email as db1_Email,
Password as db1_Password,
Request_Id as db1_Request_Id,
User_Id as db1_User_Id,
Request_name as db1_Request_name
from User
inner join User_request
on User_request.User_Id = user.ID
) AS DB1_VIEW
LEFT OUTER JOIN
(
Select ID as db2_ID,
First_name as db2_First_name,
Last_name as db2_Last_name,
Email as db2_Email,
Password as db2_Password,
Request_Id as db2_Request_Id,
User_Id as db2_User_Id,
Request_name as db2_Request_name
from User
inner join User_request
on User_request.User_Id = user.ID
) AS DB2_VIEW
ON db2_ID = db1_ID
LEFT OUTER JOIN
(
Select ID as db3_ID,
First_name as db3_First_name,
Last_name as db3_Last_name,
Email as db3_Email,
Password as db3_Password,
Request_Id as db3_Request_Id,
User_Id as db3_User_Id,
Request_name as db3_Request_name
from User
inner join User_request
on User_request.User_Id = user.ID
) AS DB3_VIEW
ON db3_ID = db1_ID
ID First_name Last_name Email Password Request_Id User_Id Request_name
1 Oliver Jake OJake#domain.com 123 1 1 Request1
2 Mathew Harry MHarry#domain.com 123 1 2 Request1
3 Jacob Reece JReece#domain.com 123 1 3
Request1
4 Charlie Damian CDamian#domain.com 123 1 4 Request1

Answer 1

Use this as your first select statement:
SELECT DB1_VIEW.*
,CASE WHEN DB2_VIEW.db2_ID IS NOT NULL THEN 'Y' ELSE 'N' END AS Available_db2
,CASE WHEN DB3_VIEW.db3_ID IS NOT NULL THEN 'Y' ELSE 'N' END AS Available_db3
You can remove all the details apart from the ID fields in the db2_view and db3_view subqueries.

Answer 2

You can use the below query before execute you should use replace [SourceDB] to your source database and [TargertDB] to your target database. Insert the table name into #mdtables to include for comparison.
USE [SourceDB]
IF Object_id('tempdb..#mdTables') IS NOT NULL
DROP TABLE #mdtables;
CREATE TABLE #mdtables
(
id INT IDENTITY(1, 1) NOT NULL,
schemaname NVARCHAR(128),
tablename NVARCHAR(128)
);
INSERT INTO #mdtables
(schemaname,
tablename)
VALUES ('dbo',
'user');
DECLARE #mdTableLim INT =0,
#mdTableRowId INT =0
SELECT #mdTableLim = Count(*)
FROM #mdtables;
SET #mdTableRowId = 1;
WHILE #mdTableRowId <= #mdTableLim
BEGIN
DECLARE #SDBName VARCHAR(50) = '[SourceDB]',
#TDBName VARCHAR(50) = '[TargertDB]',
#tableName VARCHAR(100) = ''
DECLARE #WhereF VARCHAR(max) ='',
#joincondition VARCHAR(max) ='',
#or VARCHAR(10) ='',
#select VARCHAR(max) = '',
#comma VARCHAR(1)='',
#query VARCHAR(max) ='',
#and VARCHAR(5)='',
#where1 VARCHAR(1000) ='',
#wOR VARCHAR(5)=''
SELECT #tableName = tablename
FROM #mdtables
WHERE id = #mdTableRowId;
SELECT #joincondition += Isnull(#and + ( CASE
WHEN cu.column_name IS NULL
THEN
NULL
ELSE ' src.[' + cu.column_name
+
'] = ' +
'trgt.['
+ c.column_name + ']'
END ), ''),
#WhereF += Isnull (#or + ( CASE
WHEN cu.column_name IS NOT NULL THEN
NULL
ELSE Isnull ( ' src.[' +
TC.column_name
+
'] ',
' isnull( src.[' +
C.column_name +
'],1) ' )
+ Isnull( '<> trgt.[' +
TC.column_name
+ ']',
' = isnull (src.['
+
C.column_name + '],1) ')
END ), ''),
#or = ( CASE
WHEN cu.column_name IS NOT NULL THEN ''
ELSE ' OR '
END ),
#and = ( CASE
WHEN cu.column_name IS NULL THEN ''
ELSE ' AND '
END ),
#select += #comma + ' src.[' + c.column_name + '] '
+ Isnull (' , trgt.[' + TC.column_name + ']', ''),
#comma = ',',
#where1 += Isnull(( #wOR + ( CASE
WHEN cu.column_name IS NULL THEN
NULL
ELSE ' trgt.[' + cu.column_name +
'] is null '
END ) ), ''),
#wOR = ( CASE
WHEN cu.column_name IS NULL THEN ''
ELSE ' OR '
END )
FROM information_schema.columns C
LEFT JOIN information_schema.key_column_usage CU
ON C.column_name = cu.column_name
AND constraint_name LIKE 'PK_%'
AND c.table_name = cu.table_name
LEFT JOIN [TargertDB].information_schema.columns TC
ON C.column_name = TC.column_name
AND c.table_name = TC.table_name
WHERE c.table_name = #tableName
--AND columnproperty(object_id(TABLE_NAME), COLUMN_NAME, 'IsIdentity') = 0
AND c.column_name NOT IN ( 'LST_CHG_TMS', 'LST_CHG_TMS',
'LST_CHG_USR_ID'
,
'LST_CHG_USR_ID' )
AND c.data_type NOT IN ( 'image' )
ORDER BY cu.column_name
SET #query = 'select ' + #select + ' from ' + #SDBName + '.dbo.'
+ #tableName + ' as src left join ' + #TDBName
+ '.dbo.' + #tableName + ' as trgt on '
+ #joincondition + ' where (' + #where1 + ')'
+ Isnull ('and '+ NULLIF (#WhereF, ''), '')
DECLARE #qu1 VARCHAR(max) =
' declare #cnt int =0 select #cnt =count (1) from '
+ #SDBName + '.dbo.' + #tableName
+ ' as src left join ' + #TDBName + '.dbo.'
+ #tableName + ' as trgt on ' + #joincondition
+ ' where (' + #where1 + ')'
+ Isnull (' OR '+ NULLIF (#WhereF, ''), '')
+ ' if (#cnt>0) begin select '''
+ #tableName + ''' as [ ],#cnt ' +-- #query + ' end '
BEGIN try
EXECUTE ( #qu1)
END try
BEGIN catch
PRINT #qu1;
END catch
SET #mdTableRowId = #mdTableRowId + 1
END

Answer 3

This might not need CTE's or sub-queries.
A few joins might do it.
SELECT
Usr1.ID AS db1_User_Id,
Usr1.First_name AS db1_First_name,
Usr1.Last_name AS db1_Last_name,
Usr1.Email AS db1_Email,
Usr1.Password AS db1_Password,
MAX(UsrReq1.Request_Id) AS db1_Request_Id,
MAX(UsrReq1.Request_name) AS db1_Request_name,
CASE WHEN COUNT(UsrReq2.User_Id) > 0 THEN 'Y' ELSE 'N' END AS Available_Db2,
CASE WHEN COUNT(UsrReq3.User_Id) > 0 THEN 'Y' ELSE 'N' END AS Available_Db3
FROM [Database1].[User] AS Usr1
LEFT JOIN [Database1].[User_request] AS UsrReq1 ON UsrReq1.User_Id = Usr1.ID
LEFT JOIN [Database2].[User] AS Usr2 ON Usr2.ID = Usr1.ID
LEFT JOIN [Database2].[User_request] AS UsrReq2 ON UsrReq2.User_Id = Usr2.ID
LEFT JOIN [Database3].[User] AS Usr3 ON Usr3.ID = Usr1.ID
LEFT JOIN [Database3].[User_request] AS UsrReq3 ON UsrReq3.User_Id = Usr3.ID
GROUP BY
Usr1.ID,
Usr1.First_name,
Usr1.Last_name,
Usr1.Email,
Usr1.Password;