I need to generate query like this:
SELECT **DISTINCT ON** (article.code) article.code, article.title
First I try to make it via ORM distinct method and send it a list with fields. But it wont work. Second, I try to make it via sqlalchemy.sql.select - and it also generate sql query like this:
SELECT DISTINCT article.code, article.title
I Need SELECT **DISTINCT ON** (article.code)...
I look at source code and found in sqlalchemy.dialects.postgresql.base.PGCompiler.get_select_precolumns code for generating constructions like: 'DISTINCT ON'
But this method do not called. Instead of this called another method - sqlalchemy.sql.compiler.get_select_precolumns - it hasn't code for generating DISTINCT ON only for DISTINCT Maybe I should configure my session to called properly method?
This bug report suggests that DISTINCT ON works correctly in SQLAlchemy 0.7+. I think an upgrade is in order, unless you've uncovered a bug in 0.7.
Workarounds . . .
Volunteer to help get the 0.7 package
ready for Ubuntu.
Download and install from
source.
Rewrite queries to avoid DISTINCT
ON. I'm not sure whether that's
possible in the most general case.
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 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).
I want to do something like this in OrmLite
SELECT *, COUNT(title) as titleCount from table1 group by title;
Is there any way to do this via QueryBuilder without the need for queryRaw?
The documentation states that the use of COUNT() and the like necessitates the use of selectRaw(). I hoped for a way around this - not having to write my SQL as strings is the main reason I chose to use ORMLite.
http://ormlite.com/docs/query-builder
selectRaw(String... columns):
Add raw columns or aggregate functions
(COUNT, MAX, ...) to the query. This will turn the query into
something only suitable for using as a raw query. This can be called
multiple times to add more columns to select. See section Issuing Raw
Queries.
Further information on the use of selectRaw() as I was attempting much the same thing:
Documentation states that if you use selectRaw() it will "turn the query into" one that is supposed to be called by queryRaw().
What it does not explain is that normally while multiple calls to selectColumns() or selectRaw() are valid (if you exclusively use one or the other),
use of selectRaw() after selectColumns() has a 'hidden' side-effect of wiping out any selectColumns() you called previously.
I believe that the ORMLite documentation for selectRaw() would be improved by a note that its use is not intended to be mixed with selectColumns().
QueryBuilder<EmailMessage, String> qb = emailDao.queryBuilder();
qb.selectColumns("emailAddress"); // This column is not selected due to later use of selectRaw()!
qb.selectRaw("COUNT (emailAddress)");
ORMLite examples are not as plentiful as I'd like, so here is a complete example of something that works:
QueryBuilder<EmailMessage, String> qb = emailDao.queryBuilder();
qb.selectRaw("emailAddress"); // This can also be done with a single call to selectRaw()
qb.selectRaw("COUNT (emailAddress)");
qb.groupBy("emailAddress");
GenericRawResults<String[]> rawResults = qb.queryRaw(); // Returns results with two columns
Is there any way to do this via QueryBuilder without the need for queryRaw(...)?
The short answer is no because ORMLite wouldn't know what to do with the extra count value. If you had a Table1 entity with a DAO definition, what field would the COUNT(title) go into? Raw queries give you the power to select various fields but then you need to process the results.
With the code right now (v5.1), you can define a custom RawRowMapper and then use the dao.getRawRowMapper() method to process the results for Table1 and tack on the titleCount field by hand.
I've got an idea how to accomplish this in a better way in ORMLite. I'll look into it.
What I'm trying to do is, if a field is blank, use another field within WRKQRY(Query/400) in define result fields. Is this possible?
You can create an SQL view using the RUNSQLSTM command and then run a query over the view.
CREATE VIEW QTEMP/MYVIEW AS
SELECT F1, CASE WHEN F2 <> ' ' THEN F2 ELSE F3 END AS FX FROM MYLIB/MYFILE
Then tie it all together with a CL program.
PGM
DLTF FILE(QTEMP/MYVIEW)
MONMSG MSGID(CPF0000)
RUNSQLSTM SRCFILE(MYLIB/MYSRC) MBR(MYMBR)
RUNQRY QRY(MYLIB/MYQRY)
ENDPGM
Query/400 is obsolete, and should be considered deprecated. It was replaced about 2 decades ago by Query Management. Query/400 queries run under the old database optimizer (CQE) and cannot benefit from newer faster optimization techniques employed by the new optimizer (SQE). It is recommended to migrate Query/400 queries to QM Query or to DB2 Web Query.
Fortunately, Query Management Queries can be created in a prompted mode which should be very familiar to Query/400 users. Prompted-mode queries can be converted to the more powerful SQL-mode.
You can use the RTVQMQRY command to generate SQL source from the Query/400 query you have asked about Once you have the source, you can then use the CASE ... END expression given by #Mike. Create the QM query with the CRTQMQRY command, and run it with STRQMQRY.
If you still need to do this, I can show you how to do it in 3 passes of Query 400.
Yeah, I know that's not efficient but it can be done.
Take a look at CASE that should work for you.
CASE field
WHEN ' ' THEN newfield
ELSE field
END as myfield
I'm using Zend Framework for my website and I'd like to retrieve some data from my PostgreSQL database.
I have a request like :
SELECT DISTINCT ON(e.id) e.*, f.*, g.* FROM e, f, g
WHERE e.id = f.id_e AND f.id = g.id_f
This request works well but I don't know how to convert the DISTINCT ON(e.id) with Zend.
It seems that I can get DISTINCT rows but no distinct columns.
$select->distinct()->from("e")->join("f", "e.id = f.id_e")
->join("g", "f.id = g.id_f");
Any idea on how to make a select with distinct column ?
Thanks for help
You probably can't do this with Zend Framework since distinct on is not part of the SQL standard (end of page in Postgres documentation). Although Postgres supports it, I would assume its not part of Zend Framework because you could in theory configure another database connection which does not offer support.
If you know in advance that you're developing for a specific database (Postgres in this case), you could use manually written statements instead. You'll gain more flexibility within the queries and better performance at the cost of no longer being able to switch databases.
You would then instantiate a Zend_Db_Apdapter for Postgres. There a various methods available to get results for SQL queries which are described in the frameworks documentation starting at section Reading Query Results. If you choose to go this route I'd recommend to create an own subclass of the Zend_Db_Adapter_Pgsql class. This is to be able to convert data types and throw exceptions in case of errors instead of returning ambiguous null values and hiding error causes.