As title shown, when reading the manul, I found type record type and row type, which are both composite type. However, I want to figure out their difference.
They're similar once defined but tend to have different use cases.
A RECORD type has no predefined structure and is typically used when the row type might change or is out of your control, for example if you're referencing a record in a FOR LOOP.
ROWTYPE is predefined of a particular table row structure and thus if anything deviates from that structure you will get runtime errors.
It all depends what you're trying to achieve.
For cursor loops I use a RECORD>
For more information:
http://www.postgresql.org/docs/current/static/plpgsql-declarations.html
Related
I'm building a framework for rust-postgres.
I need to know what value type will be returned from a row.try_get, to get the value in a variable of the appropriate type.
I can get the sql type from row.columns()[index].type, but not if the value is nullable , so i can't decide to put the value in a normal type or a Option<T>.
I can use just the content of the row to understand it, i can't do things like "get the table structure from Postgresql".
is there a way?
The reason that the Column type does not expose any way to find out if a result column is nullable is because the database does not return this information.
Remember that result columns are derived from running a query, and that query may contain arbitrary expressions. If the query was a simple SELECT of columns from a table, then it would be reasonably simple to determine if a column could be nullable.
But it could also be a very complex expression, derived from multiple columns, subselects or even custom functions. Postgres can figure out the data type of each column, but in the general case it doesn't know if a result column may contain nulls.
If your application is only performing simple queries, and you know which table column each result column comes from, then you can find out if that table column is nullable like this:
SELECT is_nullable
FROM information_schema.columns
WHERE table_schema='myschema'
AND table_name='mytable'
AND column_name='mycolumn';
If your queries are not that simple then I recommend you always get the result as an Option<T> and handle the possibility that the result might be None.
I have a DMN decision created in Decision Manager 7.3. I have a few data types created, all of which are "structures" (i.e. complex types) with nested fields. I have created a decision table of which the condition column is bound to one of these structures (Customer) and the output column is bound to a Result structure.
However, I would expect the column headers to reflect the structure of the objects as per the example here (step 9 onwards): https://access.redhat.com/documentation/en-us/red_hat_decision_manager/7.3/html-single/designing_a_decision_service_using_dmn_models/index#dmn-data-types-defining-proc_dmn-models
In the documentation example, the Loan_Qualification type has nested fields and these are shown as sub-columns in the table header.
My data types are defined as follows:
I have a Customer input node and a decision node defined as follows:
Yet in my decision table, the columns map to the top level object only as follows:
So any ideas as to what I might be missing? Thanks in advance.
UPDATE
I have used the answer given below by #karreiro which works for the outcome / action column, but inserting an Input Clause left or right adds a new top level column, not a sub column, which then looks like the following:
Is this something you expect the decision table editor to be able to do as well?
Your expectations are correct.
The DMN editor aims to support the auto-creation of fields for Structure Data Types (for output clauses https://issues.jboss.org/browse/DROOLS-3685, and input clauses https://issues.jboss.org/browse/DROOLS-4491).
However, momentarily, users need to create these fields manually:
See how to create here :-)
I've got an enum type that I've become interested in ordering in a particular way. I've written and run the SQL to impose a new ordering by sorting the labels (externally) by my new criteria and then updating the enumsortorder for all the values.
It doesn't work. I've verified that I've satisfied the (really weird) rule that the sort ordering feature works only on enum types with even oids; my oid for this type is even (58016). As far as I can tell, the ordering being imposed when I ORDER BY the enum column is exactly the same as what it was before.
Is there something else I need to do in order to make this work? The PostgreSQL documentation makes me think it should work.
Even oids have fixed ordering so you can't reorder them by modifying the pg-enum system table.
you're going to have to replace the existing enum with a new enum type. this means
Creating a new enum type
Dropping any relationships that use the enum.
Update the columns to the new type using something like
ALTER TABLE foo ALTER COLUMN bar
TYPE TO new_enum_type
USING (bar::text)::new_enum_type;
Here the cast to text matches the new enum values to the old enum values by their name.
Finally you need to recreate all the dropped relationships.
If needed you can run all this DML inside a transaction block.
Expect it to be slow if you have lots of data as it's rewriting whole
tables
Is it possible to use the %TYPE and array together?
CREATE FUNCTION role_update(
IN id "role".role_id % TYPE,
IN name "role".role_name % TYPE,
IN user_id_list "user".user_id % TYPE[],
IN permission_id_list INT[]
)
I got syntax error by this, but I don't want to duplicate any column type, so I want to use "user".user_id % TYPE instead of simply INT because then it is easier to modify any column type later.
As the manual explains here:
The type of a column is referenced by writing table_name.column_name%TYPE. Using this feature can sometimes help make a function independent of changes to the definition of a table.
The same functionality can be used in the RETURNS clause.
But there is no simple way to derive an array type from a referenced column, at least none that I would know of.
About modifying any column type later:
You are aware that this type of syntax is only a syntactical convenience to derive the type from a table column? Once created, there is no link whatsoever to the table or column involved.
It helps to keep a whole create script in sync. But id doesn't help with later changes to live objects in the database.
Related answer on dba.SE:
Array of template type in PL/pgSQL function using %TYPE
Using referenced types in function's parameters has no sense (in PostgreSQL), because its translated intermediately to actual types, and it is stored as actual types. Sorry, PostgreSQL doesn't support this functionality - something different is using referenced types inside function, where actual type is detected every first time execution in session.
This is probably a super simple question, but I'm struggling to come up with the right keywords to find it on Google.
I have a Postgres table that has among its contents a column of type text named content_type. That stores what type of entry is stored in that row.
There are only about 5 different types, and I decided I want to change one of them to display as something else in my application (I had been directly displaying these).
It struck me that it's funny that my view is being dictated by my database model, and I decided I would convert the types being stored in my database as strings into integers, and enumerate the possible types in my application with constants that convert them into their display names. That way, if I ever got the urge to change any category names again, I could just change it with one alteration of a constant. I also have the hunch that storing integers might be somewhat more efficient than storing text in the database.
First, a quick threshold question of, is this a good idea? Any feedback or anything I missed?
Second, and my main question, what's the Postgres command I could enter to make an alteration like this? I'm thinking I could start by renaming the old content_type column to old_content_type and then creating a new integer column content_type. However, what command would look at a row's old_content_type and fill in the new content_type column based off of that?
If you're finding that you need to change the display values, then yes, it's probably a good idea not to store them in a database. Integers are also more efficient to store and search, but I really wouldn't worry about it unless you've got millions of rows.
You just need to run an update to populate your new column:
update table_name set content_type = (case when old_content_type = 'a' then 1
when old_content_type = 'b' then 2 else 3 end);
If you're on Postgres 8.4 then using an enum type instead of a plain integer might be a good idea.
Ideally you'd have these fields referring to a table containing the definitions of type. This should be via a foreign key constraint. This way you know that your database is clean and has no invalid values (i.e. referential integrity).
There are many ways to handle this:
Having a table for each field that can contain a number of values (i.e. like an enum) is the most obvious - but it breaks down when you have a table that requires many attributes.
You can use the Entity-attribute-value model, but beware that this is too easy to abuse and cause problems when things grow.
You can use, or refer to my implementation solution PET (Parameter Enumeration Tables). This is a half way house between between 1 & 2.