Question

Each of our clients has a database with their own data. Each database should have exactly the same structure. How can I find columns whose datatype has been changed, where the table name and column name is the same but the datatype is not? Is there an SQL query that can do this?

Answer 1

If both databases can be restored to the same server, you can compare the two sets of system catalog views to determine the differences:

SELECT 
    TableName = t.name,
    ColumnName = c.name,
    TypeName = ty.name,
    TableName2 = t2.name,
    ColumnName2 = c2.name,
    TypeName2 = ty2.name
FROM DB1.sys.columns c
INNER JOIN DB1.sys.tables t ON c.object_id = t.object_id
INNER JOIN DB1.sys.types ty ON c.system_type_id = ty.system_type_id
INNER JOIN DB2.sys.tables t2 ON t.name = t2.Name
INNER JOIN DB2.sys.columns c2 ON c2.object_id = t2.object_id AND c.name = c2.name
INNER JOIN DB2.sys.types ty2 ON c2.system_type_id = ty2.system_type_id
WHERE
    c.system_type_id <> c2.system_type_id

Of course, you can add more columns from the sys.columns catalog view, e.g. precision and scale for types like DECIMAL(18,2), or max_length for string-based types (like VARCHAR(50) etc.) – adapt this base query as needed