💎🤖💫SQL Reloaded: Schema Differences between Database Versions - Part I: INFORMATION_SCHEMA version

During data migrations and other similar activities it's important to check what changed in the database at the various levels. Usually, it's useful to check when schemas, object names or table definitions changed, even if the changes are thoroughly documented. One can write a script to point out all the differences in one output, though it's recommended to check the differences at each level of detail. 

For this purpose one can use the INFORMATION_SCHEMA available for many of the RDBMS implementing it. This allows to easily port the scripts between platforms. The below queries were run on SQL Server 2025 in combination with Dynamics 365 schemas, though they should run on the earlier versions, incl. (Azure) SQL Databases. 

Such comparisons must be done from the both sides, this implying a FULL OUTER JOIN when writing a single SELECT statement, however the results can become easily hard to read and even interpret when the number of columns in output increases. Therefore, it's recommended to keep the number of columns at a minimum while addressing the scope, respectively break the FULL OUTER JOIN in two LEFT JOINs.

The simplest check is at schema level, and this can be easily done from both sides (note that database names needed to be replaced accordingly):

-- difference schemas (objects not available in the new schema)
SELECT *
FROM ( -- comparison
	SELECT DB1.CATALOG_NAME
	, DB1.SCHEMA_NAME
	, DB1.SCHEMA_OWNER
	, DB1.DEFAULT_CHARACTER_SET_NAME
	, DB2.SCHEMA_OWNER NEW_SCHEMA_OWNER
	, DB2.DEFAULT_CHARACTER_SET_NAME NEW_DEFAULT_CHARACTER_SET_NAME
	, CASE 
		WHEN DB2.SCHEMA_NAME IS NULL THEN 'schema only in old db'
		WHEN DB1.SCHEMA_OWNER <> IsNull(DB2.SCHEMA_OWNER, '') THEN 'different table type'
	  END Comment
        , CASE WHEN DB1.DEFAULT_CHARACTER_SET_NAME <> DB2.DEFAULT_CHARACTER_SET_NAME THEN 'different character sets' END Character_sets
	FROM [old database_name].INFORMATION_SCHEMA.SCHEMATA DB1

	     LEFT JOIN [new database name].INFORMATION_SCHEMA.SCHEMATA DB2

	       ON DB1.SCHEMA_NAME = DB2.SCHEMA_NAME
 ) DAT
WHERE DAT.Comment IS NOT NULL
ORDER BY DAT.CATALOG_NAME
, DAT.SCHEMA_NAME


-- difference schemas (new objects)
SELECT *
FROM ( -- comparison
	SELECT DB1.CATALOG_NAME
	, DB1.SCHEMA_NAME
	, DB1.SCHEMA_OWNER
	, DB1.DEFAULT_CHARACTER_SET_NAME
	, DB2.SCHEMA_OWNER OLD_SCHEMA_OWNER
	, DB2.DEFAULT_CHARACTER_SET_NAME OLD_DEFAULT_CHARACTER_SET_NAME
	, CASE 
		WHEN DB2.SCHEMA_NAME IS NULL THEN 'schema only in old db'
		WHEN DB1.SCHEMA_OWNER <> IsNull(DB2.SCHEMA_OWNER, '') THEN 'different table type'
	  END Comment
        , CASE WHEN DB1.DEFAULT_CHARACTER_SET_NAME <> DB2.DEFAULT_CHARACTER_SET_NAME THEN 'different character sets' END Character_sets
	FROM [new database name].INFORMATION_SCHEMA.SCHEMATA DB1
	     LEFT JOIN [old database name].INFORMATION_SCHEMA.SCHEMATA DB2
	       ON DB1.SCHEMA_NAME = DB2.SCHEMA_NAME
 ) DAT
WHERE DAT.Comment IS NOT NULL
ORDER BY DAT.CATALOG_NAME
, DAT.SCHEMA_NAME

Comments:
1) The two queries can be easily combined via a UNION ALL, though it might be a good idea then to add a column to indicate the direction of the comparison. 

The next step would be to check which objects has been changed:

-- table-based objects only in the old schema (tables & views)
SELECT *
FROM ( -- comparison
	SELECT DB1.TABLE_CATALOG
	, DB1.TABLE_SCHEMA
	, DB1.TABLE_NAME
	, DB1.TABLE_TYPE
	, DB2.TABLE_CATALOG NEW_TABLE_CATALOG
	, DB2.TABLE_TYPE NEW_TABLE_TYPE
	, CASE 
		WHEN DB2.TABLE_NAME IS NULL THEN 'objects only in old db'
		WHEN DB1.TABLE_TYPE <> IsNull(DB2.TABLE_TYPE, '') THEN 'different table type'
		--WHEN DB1.TABLE_CATALOG <> IsNull(DB2.TABLE_CATALOG, '') THEN 'different table catalog'
	  END Comment
	FROM [old database name].INFORMATION_SCHEMA.TABLES DB1
	    LEFT JOIN [new database name].INFORMATION_SCHEMA.TABLES DB2
	      ON DB1.TABLE_SCHEMA = DB2.TABLE_SCHEMA
	     AND DB1.TABLE_NAME = DB2.TABLE_NAME
 ) DAT
WHERE DAT.Comment IS NOT NULL
ORDER BY DAT.TABLE_SCHEMA
, DAT.TABLE_NAME

Comments:
1) If the database was imported under another name, then the TABLE_CATALOG will have different values as well.

At column level, the query increases in complexity, given the many aspects that must be considered:

-- difference columns (columns not available in the new scheam, respectively changes in definitions)
SELECT *
FROM ( -- comparison
	SELECT DB1.TABLE_CATALOG
	, DB1.TABLE_SCHEMA
	, DB1.TABLE_NAME
	, DB1.COLUMN_NAME 
	, DB2.TABLE_CATALOG NEW_TABLE_CATALOG
	, CASE WHEN DB2.TABLE_NAME IS NULL THEN 'column only in old db' END Comment
	, DB1.DATA_TYPE
	, DB2.DATA_TYPE NEW_DATA_TYPE
	, CASE WHEN DB2.TABLE_NAME IS NOT NULL AND IsNull(DB1.DATA_TYPE, '') <> IsNull(DB2.DATA_TYPE, '') THEN 'Yes' END Different_data_type
	, DB1.CHARACTER_MAXIMUM_LENGTH
	, DB2.CHARACTER_MAXIMUM_LENGTH NEW_CHARACTER_MAXIMUM_LENGTH
	, CASE WHEN DB2.TABLE_NAME IS NOT NULL AND IsNull(DB1.CHARACTER_MAXIMUM_LENGTH, '') <> IsNull(DB2.CHARACTER_MAXIMUM_LENGTH, '') THEN 'Yes' END Different_maximum_length
	, DB1.NUMERIC_PRECISION
	, DB2.NUMERIC_PRECISION NEW_NUMERIC_PRECISION
	, CASE WHEN DB2.TABLE_NAME IS NOT NULL AND IsNull(DB1.NUMERIC_PRECISION, '') <> IsNull(DB2.NUMERIC_PRECISION, '') THEN 'Yes' END Different_numeric_precision
	, DB1.NUMERIC_SCALE
	, DB2.NUMERIC_SCALE NEW_NUMERIC_SCALE
	, CASE WHEN DB2.TABLE_NAME IS NOT NULL AND IsNull(DB1.NUMERIC_SCALE, '') <> IsNull(DB2.NUMERIC_SCALE,'') THEN 'Yes' END Different_numeric_scale
	, DB1.CHARACTER_SET_NAME
	, DB2.CHARACTER_SET_NAME NEW_CHARACTER_SET_NAME
	, CASE WHEN DB2.TABLE_NAME IS NOT NULL AND IsNull(DB1.CHARACTER_SET_NAME, '') <> IsNull(DB2.CHARACTER_SET_NAME, '') THEN 'Yes' END Different_character_set_name 
	, DB1.COLLATION_NAME
	, DB2.COLLATION_NAME NEW_COLLATION_NAME
	, CASE WHEN DB2.TABLE_NAME IS NOT NULL AND IsNull(DB1.COLLATION_NAME, '') <> IsNull(DB2.COLLATION_NAME, '') THEN 'Yes' END Different_collation_name
	, DB1.ORDINAL_POSITION
	, DB2.ORDINAL_POSITION NEW_ORDINAL_POSITION
	, DB1.COLUMN_DEFAULT
	, DB2.COLUMN_DEFAULT NEW_COLUMN_DEFAULT
	, DB1.IS_NULLABLE
	, DB2.IS_NULLABLE NEW_IS_NULLABLE
	FROM [old database name].INFORMATION_SCHEMA.COLUMNS DB1
	    LEFT JOIN [new database name].INFORMATION_SCHEMA.COLUMNS DB2

	      ON DB1.TABLE_SCHEMA = DB2.TABLE_SCHEMA
	     AND DB1.TABLE_NAME = DB2.TABLE_NAME
	     AND DB1.COLUMN_NAME = DB2.COLUMN_NAME
 ) DAT
WHERE DAT.Comment IS NOT NULL
  OR IsNull(DAT.Different_data_type,'') = 'Yes'
  OR IsNull(DAT.Different_maximum_length,'') = 'Yes'
  OR IsNull(DAT.Different_numeric_precision,'') = 'Yes'
  OR IsNull(DAT.Different_numeric_scale,'') = 'Yes'
  OR IsNull(DAT.Different_character_set_name,'') = 'Yes'
  OR IsNull(DAT.Different_collation_name,'') = 'Yes'
ORDER BY DAT.TABLE_SCHEMA
, DAT.TABLE_NAME
, DAT.COLLATION_NAME

Comments:
1) The query targets only the most common scenarios, therefore must be changed to handle further cases (e.g. different column defaults, different attributes like nullable, etc.)!
2) The other perspective can be obtained by inverting the table names (without aliases) and changing the name of the columns from "NEW_' to "OLD_" (see the queries for schemas).
3) One can move the column-based conditions for the differences in the main query, though then is needed to duplicate the logic, which will make the code more challenging to change and debug. 

Happy coding!