If I have the following query
select * from cypher('agload_test_graph', $$ match (n) with n where n.name='A' return n $$) as (sp agtype)
then n.name='A' doesn't work.
but if I remove with clause, then it works.
select * from cypher('agload_test_graph', $$ match (n) where n.name='A' return n $$) as (sp agtype)
I tried the example query in age document.
SELECT *
FROM cypher('graph_name', $$
MATCH (david {name: 'David'})-[]-(otherPerson)-[]->()
WITH otherPerson, count(*) AS foaf
WHERE foaf > 1RETURN otherPerson.name
RETURN otherPerson.name
$$) as (name agtype);
The problem with your first query is that the WHERE clause is not applied to the n variable because the WHERE clause is used before the WITH clause. By WITHclause, a new variable that is a subset of the previous variable is created in Cypher. Any filters added after the the WITH clause will be applied to this new variable rather than the original variable. By deleting the WITH clause from your second query, the where clause is being applied directly to the n variable, which is what you want.
The example query in the age document you provided is a legitimate Cypher query. It uses MATCH to find a node with the name "David", then it uses WITH clause to create a new variable otherPerson, which is the set of nodes nodes connected to the "David" node, and then uses count(*) function to count the number of nodes connected to the "David" node. After this it uses the WHERE clause to filter otherPerson nodes where the count of their connections is greater than 1 and return their names.
The where clause after with is ignored. This is one of the issues in Apache Age which is opened on github. Issue Page
Related
When using primitive types such as Integer, I can without any problems do a query like this:
with connection.cursor() as cursor:
cursor.execute(sql='''SELECT count(*) FROM account
WHERE %(pk)s ISNULL OR id %(pk)s''', params={'pk': 1})
Which would either return row with id = 1 or it would return all rows if pk parameter was equal to None.
However, when trying to use similar approach to pass a list/tuple of IDs, I always produce a SQL syntax error when passing empty/None tuple, e.g. trying:
with connection.cursor() as cursor:
cursor.execute(sql='''SELECT count(*) FROM account
WHERE %(ids)s ISNULL OR id IN %(ids)s''', params={'ids': (1,2,3)})
works, but passing () produces SQL syntax error:
psycopg2.ProgrammingError: syntax error at or near ")"
LINE 1: SELECT count(*) FROM account WHERE () ISNULL OR id IN ()
Or if I pass None I get:
django.db.utils.ProgrammingError: syntax error at or near "NULL"
LINE 1: ...LECT count(*) FROM account WHERE NULL ISNULL OR id IN NULL
I tried putting the argument in SQL in () - (%(ids)s) - but that always breaks one or the other condition. I also tried playing around with pg_typeof or casting the argument, but with no results.
Notes:
the actual SQL is much more complex, this one here is a simplification for illustrative purposes
as a last resort - I could alter the SQL in Python based on the argument, but I really wanted to avoid that.)
At first I had an idea of using just 1 argument, but replacing it with a dummy value [-1] and then using it like
cursor.execute(sql='''SELECT ... WHERE -1 = any(%(ids)s) OR id = ANY(%(ids)s)''', params={'ids': ids if ids else [-1]})
but this did a Full table scan for non empty lists, which was unfortunate, so a no go.
Then I thought I could do a little preprocessing in python and send 2 arguments instead of just the single list- the actual list and an empty list boolean indicator. That is
cursor.execute(sql='''SELECT ... WHERE %(empty_ids)s = TRUE OR id = ANY(%(ids)s)''', params={'empty_ids': not ids, 'ids': ids})
Not the most elegant solution, but it performs quite well (Index scan for non empty list, Full table scan for empty list - but that returns the whole table anyway, so it's ok)
And finally I came up with the simplest solution and quite elegant:
cursor.execute(sql='''SELECT ... WHERE '{}' = %(ids)s OR id = ANY(%(ids)s)''', params={'ids': ids})
This one also performs Index scan for non empty lists, so it's quite fast.
From the psycopg2 docs:
Note You can use a Python list as the argument of the IN operator using the PostgreSQL ANY operator.
ids = [10, 20, 30]
cur.execute("SELECT * FROM data WHERE id = ANY(%s);", (ids,))
Furthermore ANY can also work with empty lists, whereas IN () is a SQL syntax error.
TSQL - Need to query a database column which is populated by XML.
The Database has an iUserID column with an Application ID and VCKey
TxtValue is the Column name and the contained Data is similar to this
<BasePreferencesDataSet xmlns="http://tempuri.org/BasePreferencesDataSet.xsd">
<ViewModesTable>
<iViewID>1</iViewID>
</ViewModesTable>
<ViewMode_PreferenceData>
<iViewID>1</iViewID>
<iDataID>0</iDataID>
<strValue>False</strValue>
</ViewMode_PreferenceData>
<ViewMode_PreferenceData>
<iViewID>1</iViewID>
<iDataID>5</iDataID>
<strValue>True</strValue>
</ViewMode_PreferenceData>
<ViewMode_PreferenceData>
<iViewID>1</iViewID>
<iDataID>6</iDataID>
<strValue>True</strValue>
</ViewMode_PreferenceData>
<ViewMode_PreferenceData>
<iViewID>1</iViewID>
<iDataID>4</iDataID>
<strValue>False</strValue>
I want to be able to identify any iUserID in which the StrValue for iDataID's 5 and 6 are not set to True.
I have attempted to use a txtValue Like % statement but even if I copy the contents and query for it verbatim it will not yield a result leading me to believe that the XML data cannot be queried in this manner.
Screenshot of Select * query for this DB for reference
You can try XML-method .exist() together with an XPath with predicates:
WITH XMLNAMESPACES(DEFAULT 'http://tempuri.org/BasePreferencesDataSet.xsd')
SELECT *
FROM YourTable
WHERE CAST(txtValue AS XML).exist('/BasePreferencesDataSet
/ViewMode_PreferenceData[iDataID=5 or iDataID=6]
/strValue[text()!="True"]')=1;
The namespace-declaration is needed to address the elements without a namespace prefix.
The <ViewMode_PreferenceData> is filtered for the fitting IDs, while the <strValue> is filtered for a content !="True". This will return any data row, where there is at least one entry, with an ID of 5 or 6 and a value not equal to "True".
So without sample data (including tags; sorry you're having trouble with that) it's tough to craft the complete query, but what you're looking for is XQuery, specifically the .exists method in T-SQL.
Something like
SELECT iUserID
FROM tblLocalUserPreferences
WHERE iApplicationID = 30
AND vcKey='MonitorPreferences'
AND (txtValue.exist('//iDataID[text()="5"]/../strValue[text()="True"]') = 0
OR txtValue.exist('//iDataID[text()="6"]/../strValue[text()="True"]')=0)
This should return all userID's where either iDataID 5 or 6 do NOT contain True. In other words, if both are true, you won't get that row back.
I want to convert an SQL query into a JSONiq Query, is there already an implementation for this, if not, what do I need to know to be able to create a program that can do this ?
I am not aware of an implementation, however, it is technically feasible and straightforward. JSONiq has 90% of its DNA coming from XQuery, which itself was partly designed by people involved in SQL as well.
From a data model perspective, a table is mapped to a collection and each row of the table is mapped to a flat JSON object, i.e., all fields are atomic values, like so:
{
"Name" : "Turing",
"First" : "Alan",
"Job" : "Inventor"
}
Then, the mapping is done by converting SELECT-FROM-WHERE queries to FLWOR expressions, which provide a superset of SQL's functionality.
For example:
SELECT Name, First
FROM people
WHERE Job = "Inventor"
Can be mapped to:
for $person in collection("people")
where $person.job eq "Inventor"
return project($person, ("Name", "First"))
More complicated queries can also be mapped quite straight-forwardly:
SELECT Name, COUNT(*)
FROM people
WHERE Job = "Inventor"
GROUP BY Name
HAVING COUNT(*) >= 2
to:
for $person in collection("people")
where $person.job eq "Inventor"
group by $name := $person.name
where count($person) ge 2
return {
name: $name,
count: count($person)
}
Actually, if for had been called from and return had been called select, and if these keywords were written uppercase, the syntax of JSONiq would be very similar to that of SQL: it's only cosmetics.
I'm trying to do a SELECT COUNT(*) with Postgres.
What I need: Catch the rows affected by the query. It's a school system. If the student is not registered, do something (if).
What I tried:
$query = pg_query("SELECT COUNT(*) FROM inscritossimulado
WHERE codigo_da_escola = '".$CodEscola."'
AND codigo_do_simulado = '".$simulado."'
AND codigo_do_aluno = '".$aluno."'");
if(pg_num_rows($query) == 0)
{
echo "Error you're not registered!";
}
else
{
echo "Hello!";
}
Note: The student in question IS NOT REGISTERED, but the result is always 1 and not 0.
For some reason, when I "show" the query, the result is: "Resource id #21". But, I look many times in the table, and the user is not there.
You are counting the number of rows in the answer, and your query always returns a single line.
Your query says: return one row giving the number of students matching my criteria. If no one matches, you will get back one row with the value 0. If you have 7 people matching, you will get back one row with the value 7.
If you change your query to select * from ... you will get the right answer from pg_num_rows().
Actually, don't count at all. You don't need the count. Just check for existence, which is proven if a single row qualifies:
$query = pg_query(
'SELECT 1
FROM inscritossimulado
WHERE codigo_da_escola = $$' . $CodEscola . '$$
AND codigo_do_simulado = $$' . $simulado. '$$
AND codigo_do_aluno = $$' . $aluno . '$$
LIMIT 1');
Returns 1 row if found, else no row.
Using dollar-quoting in the SQL code, so we can use the safer and faster single quotes in PHP (I presume).
The problem with the aggregate function count() (besides being more expensive) is that it always returns a row - with the value 0 if no rows qualify.
But this still stinks. Don't use string concatenation, which is an open invitation for SQL injection. Rather use prepared statements ... Check out PDO ...
say i have a nvarchar field in my database that looks like this
1, "abc abccc dabc"
2, "abccc dabc"
3, "abccc abc dabc"
i need a select LINQ query that would match the word "abc" with boundaries not part of a string
in this case only row 1 and 3 would match
from row in table.AsEnumerable()
where row.Foo.Split(new char[] {' ', '\t'}, StringSplitOptions.None)
.Contains("abc")
select row
It's important to include the call to AsEnumerable, which means the query is executed on the client-side, else (I'm pretty sure) the Where clause won't get converted into SQL succesfully.
Maybe a regular expression like this (nb - not compiled or tested):
var matches = from a in yourCollection
where Regex.Match(a.field, ".*\sabc\s.*")
select a;
datacontext.Table.Where(
e => Regex.Match(e.field, #"(.*?[\s\t]|^)abc([\s\t].*?|$)")
);
or
datacontext.Table.Where(
e => e.Split(' ', '\t').Contains("abc");
);
For efficiency, you want to do as much of the filtering as possible on the server, and then the rest of the filtering on the client. You can't use Regex on the server (SQL Server doesn't support it) so the solution is to first use a LIKE-type search (by calling .Contains) then use Regex on the client to further refine the results:
db.MyTable
.Where (t => t.MyField.Contains ("abc"))
.AsEnumerable() // Executes locally from this point on
.Where (t => Regex.IsMatch (t.MyField, #"\babc\b"))
This ensures that you retrieve only the rows from SQL Server than contain the letters 'abc' (regardless of whether they're a word-boundary match or not) and use Regex on the client-side to further restrict the result set so that only matches that are on word boundaries are included.