This is my first post to a PostgreSQL mailing list, so please forgive me if I have posted to the wrong place

Currently pg_dump has flags for dumping only table definitions and/or data. These flags are respectively:

I propose that two more be added:

These would essentially break up the output of --schema-only into two sections. I.e., the output of --tables-only plus the output of --constraints-only would be identical to the output of --schema-only .

There are a number of scenarios where this may be useful, I will describe the one that I would use it for.

When making changes to my database schema I would like to take the schema from the newly modified database, and dump the data from the old database into it to ensure that the new schema is able to take the data that exists in the live database. If it isn't then I modify the new schema or the live dataset as appropriate, and try again.

This requires the following steps:

1. Create temporary database and apply modified schema to it
2. Dump new database using --schema-only
3. Split new schema into table definitions and constraints
4. Apply new schema table definitions from step 34 to the testing database
5. Dump the existing database using --data-only
6. Apply the dataset from step 5 to the testing database
7. Apply new schema constraints from step 3 to the testing database

All of these steps are easily scriptable except step 3, which means that making quick changes to the new schema and re-applying includes the tedious task of opening the 5,000 line schema file in a text editor and manually pasting the relevant sections into new files. Step 3 really does hold up the development process with regards to testing changes to the schema.

Generalizing the nature of this task, the pg_dump features I propose would allow the easy scripting of dumping databases, making changes to the dumps and then re-applying them in a non paradox-inducing order.

FWIW I thought this would be a very simple patch, and had a look at the code for pg_dump myself, despite the fact that I've not even written a Hello World in C as yet. That attempt failed miserably, so now I am reduced to selling the merits of this idea to real developers. Incidentally, --schema-only appears to break tables and constraints into two sections already, as evidenced by the fact that all tables are created first, and constraints afterwards.

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