I have some data in a postgres table with one column called version (of type varchar). I would like to use my own comparison function to to order/sort on that column, but I am not sure what is the most appropriate answer:
I have an JS implementation of the style comp(left, right) -> -1/0/1, but I don't know how I can use it in a sql order by clause (through plv8)
I could write a C extension, but I am not particularly excited about this (mostly for maintenance reason, as writing the comparison in C would not be too difficult in itself)
others ?
The type of comparisons I am interested are similar to version string ordering used in package managers.
You want:
ORDER BY mycolumn USING operator
See the docs for SELECT. It looks like you may need to define an operator for the function, and a b-tree operator class containing the operator to use it; you can't just write USING myfunc().
(No time to test this and write a demo right now).
Related
I was creating a function following an example from a database class which included the creation of a temporary variable (base_salary) and using a SELECT INTO to calculate its value later.
However, I did not realize I used a different order for the syntax (SELECT ... FROM ... INTO base_salary) and the function could be used later without any visible issues (values worked as expected).
Is there any difference in using "SELECT ... FROM ... INTO" syntax order? I tried looking about it in the PostgreSQL documentation but found nothing about it. Google search did not provide any meaningful information neither. Only thing I found related to it was from MySQL documentation, which only mentioned about supporting the different order in an older version.
There is no difference. From the docs of pl/pgsql:
The INTO clause can appear almost anywhere in the SQL command.
Customarily it is written either just before or just after the list of
select_expressions in a SELECT command, or at the end of the command for other command types. It is recommended that you follow
this convention in case the PL/pgSQL parser becomes stricter in future
versions.
Notice that in (non-procedural) SQL, there is also a SELECT INTO command which works like CREATE TABLE AS, in this version the INTO must come right after the SELECT clause.
I always use SELECT ... INTO ... FROM , I believe that is the standard supported notation
https://www.w3schools.com/sql/sql_select_into.asp
I would recommend using this, also if there are any updates or if the other version might become unsupported as you mentioned...
I've created a Postgresql database with a few tables and am fairly content with how they work. I've also written some Ada code to interface with and perform simple queries. This all running on Slackware 14.2 using GNAT 2020.
One of my table columns is of an array type, an array of BIGINT.
The problem I have is when I try to create the schema for my Ada using gnatcoll_db2ada.
The schema file ("all-schema.txt") includes the following line:
item_list | BIGINT[] | | | |
When I do
gnatcoll_db2ada -dbmodel all-schema.txt
I get
Error: unknown field type "BIGINT[]"
all-schema.txt:33 gnatcoll-sql-inspect.adb:1420
gnatcoll-sql-inspect.adb:1420
Is what I'm trying to do actually possible?
The documentation suggests that database fields of array types are not supported (i.e. they are not mentioned as being supported). From the document SQL: Database interface:
The type of the field is the SQL type ("INTEGER", "TEXT", "TIMESTAMP", "DATE", "DOUBLE PRECISION", "MONEY", "BOOLEAN", "TIME", "CHARACTER(1)"). Any maximal length can be specified for strings, not just 1 as in this example. The tool will automatically convert these to Ada when generating Ada code. A special type ("AUTOINCREMENT") is an integer that is automatically incremented according to available ids in the table. The exact type used will depend on the specific DBMS.
Note that while the scalar field type "BIGINT" is not mentioned in the documentation, it is mentioned in the source code (see gnatcoll-sql.ads).
If you really need support for the "BIGINT" array type, then a quick glance at the source code suggests that you can extend the GNATCOLL DB interface with new field types by
using the generic package GNATCOLL.SQL_Impl.Field_Types (see here) and
the creation of a new field mapping (i.e. a new concrete type based on GNATCOLL.SQL.Inspect.Field_Mapping, see here).
It seems that new field types are typically placed in package GNATCOLL.SQL_Fields (see here).
Note that I never did this myself, so I cannot tell how much effort it will be and whether this is really all that is needed; The exact requirements for implementing a new field type are (at the time of writing) not documented.
I suspected as much, having briefly looked at the source.
What I'll do is spin off the array into another table. This at least has helped clarify what I need to, and the array, to be fair, always felt a bit clunky. Thanks for the the comments.
I'm using pg-promise and am not understanding how to run this query. The first query works, but I would like to use pg-promise's safe character escaping, and then I try the second query it doesn't work.
Works:
db.any(`SELECT title FROM books WHERE id = ANY ('{${ids}}') ORDER BY id`)
Doesn't work
db.any(`SELECT title FROM books WHERE id = ANY ($1) ORDER BY id`, ids)
The example has 2 problems. First, it goes against what the documentation tells you:
IMPORTANT: Never use the reserved ${} syntax inside ES6 template strings, as those have no knowledge of how to format values for PostgreSQL. Inside ES6 template strings you should only use one of the 4 alternatives - $(), $<>, $[] or $//.
Manual query formatting, like in your first example, is a very bad practice, resulting in bad things, ranging from broken queries to SQL injection.
And the second issue is that after switching to the correct SQL formatting, you should use the CSV Filter to properly format the list of values:
db.any(`SELECT title FROM books WHERE id IN ($/ids:csv/) ORDER BY id`, {ids})
or via an index variable:
db.any(`SELECT title FROM books WHERE id IN ($1:csv) ORDER BY id`, [ids])
Note that I also changed from ANY to IN operand, as we are providing a list of open values here.
And you can use filter :list interchangeably, whichever you like.
I have next issue:
I have list of names, based on which I want to filter.The problem is that I have not full names(Because I'm receiving them from ui), and I have, for example, this array= ['Joh', 'Michae'].
So, I want to filter based on this array.
I wrote query in PostgreSQL
select * from q_ob_person where name like any (array['%Хомяченко%', '%Вартопуз%']);
And I want to ask how to write JPQL query gor this.
Is there an option to call postgresql function like any from JPQL?
JPA 2.1 allows invocation of any SQL function using
FUNCTION(sqlFuncName, sqlArgs)
So you could likely do something like (note never tried this LIKE ANY you refer to, just play around with it)
FUNCTION("LIKE", FUNCTION("ANY", arrayField))
Obviously by invoking SQL functions specific to a particular RDBMS you lose database independence (in case that's of importance).
Is there some scala relational database framework (anorm, squeryl, etc...) using postgres-like aggregators to produce lists after a group-by, or at least simulating its use?
I would expect two levels of implementation:
a "standard" one, where at least any SQL grouping with array_agg is translated to a List of the type which is being aggregated,
and a "scala ORM powered" one where some type of join is allowed so that if the aggregation is a foreign key to other table, a List of elements of the other table is produced. Of course this last thing is beyond the reach of SQL, but if I am using a more powerful language, I do not mind some steroids.
I find specially intriguing that the documentation of slick, which is based precisely in allowing scala group-by notation, seems to negate explicitly the output of lists as a result of the group-by.
EDIT: use case
You have the typical many-to-many table of, say, products and suppliers, pairs (p_id, s_id). You want to produce a list of suppliers for each product. So the postgresql query should be
SELECT p_id, array_agg(s_id) from t1 group by p_id
One could expect some idiomatic way to to this in slick, but I do not see how. Furthermore, if we go to some ORM, then we could also consider the join with the tables products and suppliers, on p_id and s_id respectively, and get as answer a zip (product, (supplier1, supplier2, supplierN)) containing the objects and not only the ids
I am also not sure if I understand you question correct, could you elaborate?
In slick you currently can not use postgres "array_agg" or "string_agg" as a method on type Query. If you want to use this specific function then you need to use custom sql. But: I added an issue some time ago (https://github.com/slick/slick/issues/923, you should follow this discussion) and we have a prototype from cvogt ready for this.
I needed to use "string_agg" in the past and added a patch for it (see https://github.com/mobiworx/slick/commit/486c39a7ed90c9ccac356dfdb0e5dc5c24e32d63), so maybe this is helpful to you. Look at "AggregateTest" to learn more about it.
Another possibility is to encapsulate the usage of "array_agg" in a database view and just use this view with slick. This way you do not need "array_agg" directly in slick.
You can use slick-pg.
It supports array_agg and other aggregate functions.
Your question is intriguing, care to elaborate a little on how it might ideally look? When you group by you often have an additional column, such as count(*) over and above the standard columns from your case class, so what would the type of your List be?
Most of my (anorm) methods either return a singleton (perhaps Option) or a List of that class's type. For each case class, I have an sqlFields variable (e.g. m.id, m.name, m.forManufacturer) and a single parser variable that I reference as either .as(modelParser.singleOpt) or .as(modelParser *). For foreign keys, a lazy val at the case class level (or def if it needs to be) is pretty useful. E.g. if I had Model and Manufacturer entities, with a foreign key forManufacturer on Model, then I might define a lazy val manufacturer : Manufacturer = ... in the case class of the model, so that at any time I can refer to model.manufacturer. I can define joins as their own methods, either in this way, or as methods in the companion object.
Not 100% sure I am answering your question, but thought this was a bit long for a comment.
Edit: If your driver supported parsing of postgresql arrays, you could map them directly to a class like ProductSuppliers(id:Int, suppliers:List[Int]) (or even List[Supplier]?) In anorm that's about as idiomatic as one could get, I think? For databases that don't support it, it seems to me similar to an order by version, i.e. select p1, s1 from t1 order by p1, which you could groupBy p1 and similarly map to ProductSuppliers.