The SQL generated for the row-by-row mode is like. Select columnsrequired. From comparisontable where key =:parameter order by generatedcolumn desc. So the SQL statement is preparsed and the where clause contains all the columns listed in the 'Input Primary Key Columns'.

1. Mysql Generated Column Index
2. Waters Column Comparison Chart
3. Generated Column Mysql
4. Generated Key Column In Table Comparison Chart

By: Matteo Lorini Updated: 2017-04-18 Comments (1) Related: More >T-SQL

SQL Server allows only a single IDENTITY column per table. The result set that is returned by getGeneratedKeys method of the SQLServerStatement class will have only one column, with the returned column name of GENERATEDKEYS. If generated keys are requested on a table that has no IDENTITY column, the JDBC driver will return a null result set. What are the changes happened in source file that need to be reflected in target table,which means updated, Inserted, deleted records must be known. NOTE: – In table comparison transformation we can’t use generated key column as VARCHAR it always must be INT. Below figure 3 indicates the flow of table comparison transformation hierarchy.

Problem

Within the last 15+ years of work experience as an MSSQL DBA and Developer for small, medium and large corporations the simple task of keeping table schemas in sync amongst development, QA and production environments seems to be a recurring task. The market offers a variety of good tools that can help to synchronize SQL Server environments, however there is a quick and dirty way that can be used to compare table schemas directly from Microsoft SQL Server which we will cover in this tip.

Solution

Without the use of third party tools, one way to compare table schemas using native T-SQL is to query the INFORMATION_SCHEMA.COLUMNS metadata and build a custom made procedure or logic that compares two tables.

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Another way to do this is to use the dynamic management function sys.dm_exec_describe_first_result_set, available since SQL Server 2012 that takes a T-SQL statement as input parameter and outputs the metadata description.

Let's see how we can take advantage of this dynamic management function to build a way to compare table structures.

Create Sample Tables

Let's create two tables as follows. For simplicity I am creating these in the same database, but this could be done among different databases and even different instances of SQL Server and we could use Linked Servers and four part naming to address the objects if we want to compare against different servers.

Output from dm_exec_describe_first_result_set

Let's get familiar with the dynamic management function to see what kind of metadata information it retrieves. We will just pull back data for the usrID and usrPhonNum columns.

We can see the metadata that is returned.

Running Comparisons

Let's now compare the tables between our two tables.

You can see below that I am pulling back various columns from the dynamic management function and doing an OUTER JOIN between the two tables. This will allow me to join the two tables based on the column name.

We can see a comparison between the two datasets. We can see these tables are almost identical, except that the usrID is not an identity on WebUsers2.

Make Changes and Compare Again

Let's now change the schema of the WebUsers2 table by making column WebAddr nullable and by adding a new column named usrWebIP. We will just drop and recreate the table as follows.

We can now see the differences between the two tables.

Make More Changes and Compare

Let's change the schema of the WebUsers2 table again and re-run the compare script.

We can see the differences highlighted in blue.

Conclusion

We have seen how we can utilize a simple dynamic management function to create something meaningful and useful to quickly compare table metadata. A possible use of such function is to create a scheduled job that will detect any metadata changes from different environments.

Mysql Generated Column Index

References

• Information Schema Usage INFORMATION_SCHEMA.COLUMNS

Next Steps

• Try to use Information_Schema to create a table compare procedure.
• Check out these Information Schema Columns Tips
• Evaluate these SQL Server Comparison Tools
• Read this tip: Ways to compare and find differences for SQL Server tables and data.

About the author

To delta load a table which has a surrogate key as primary key you simply combine Table Comparison with Key Generation Transform. Behind the scenes, some not so obvious things go on.

The flow itself is simple.

The secret is the Table Comparison Transform, that perform the lookup on the target table to get the current status. With this lookup, it can read and will output all the columns, even if they are not part of the input schema. An example is the surrogate key of the target table. The Table Comparison does get the logical primary key as input, tries to find the matching row in the comparison (target) table and if found, will get all the missing column values as well like the corresponding KEY_ID.

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The only thing to watchout is, if using the row-by-row setting of the Transform, the compare table has to have an index on the logical(!!) primary key - CUSTOMER_ID in this example.

Now the Key Generation Transform gets insert and update rows but will overwrite the KEY_ID column only for rows with OP code of insert - rows that do not have a KEY_ID yet.

Waters Column Comparison Chart

And at then end, the target table loader does execute the insert or the update statement. For the update statement, it needs to know what the physical primary key is, so make sure the target table got imported with primary key column(s) into the DI repo.

Generated Column Mysql

Generated Key Column In Table Comparison Chart