I'm using nim and db_sqlite to fetch some rows with certain _ids from a database table. For example:
for row in db.fastRows("SELECT * FROM t WHERE _id IN (?, ?)", #["1", "2"]):
echo row
This works as expected, however, the sequence at the end is constructed dynamically at runtime, which means I need a variable amount of ? in the query. I end up creating a sequence with question marks, joining them, interpolating the string and turning it into a database query:
var qs : seq[string]
for id in ids:
qs.add("?")
let query_string = """SELECT * FROM t WHERE _id IN ($1)""" % join(qs, ",")
let query = SqlQuery(query_string)
for row in db.fastRows(query, ids):
echo row
Is there a better way to construct a select ... in query in nim? Ideally one with just one ? in the SqlQuery.
(For what it's worth, the current behavior is similar to other languages I've used)
you could do the replacement manually, here's one way using strformat and map
import strformat,db_sqlite,sequtils,strutils
#assuming ids is a seq[string] here
let query = sql(&"SELECT * FROM t WHERE _id IN ({ids.map(dbQuote).join(\",\")})")
for row in db.fastRows(query):
echo row
Related
Sorry for this but I'm real new to sqlite: i've created a database from an excel sheet I had, and I can't seem to fetch the values of the column I need
query = """ SELECT GNCR from table"""
cur.execute(query)
This actually works, but
query = """ SELECT ? from table"""
cur.execute(query, my_tuple)
doesn't
Here's my code:
def print_col(to_print):
db = sqlite3.connect('my_database.db')
cur = db.cursor()
query = " SELECT ? FROM my_table "
cur.execute(query, to_print)
results = cur.fetchall()
print(results)
print_col(('GNCR',))
The result is:
[('GNCR',), ('GNCR',), ('GNCR',), ('GNCR',), [...]]
instead of the actual values
What's the problem ? I can't figure it out
the "?" character in query is used for parameter substitution. Sqlite will escape the parameter you passed and replace "?" with the send text. So in effect you query after parameter substitution will be SELECT 'GNCR' FROM my_table where GNCR will be treated as text so you will get the text for each row returned by you query instead of the value of that column.
Basically you should use the query parameter where you want to substitute the parameter with escaped string like in where clause. You can't use it for column name.
I am trying to query my cassandra database to return data from a list of names held on an array server side. This is held as an array.
I know the data I am accessing is stored as a string in my database and so I have appended single quotes around it (I have tried with and without this but no luck).
Here is my query.
const arr = ["ukcust1","ukcust2","ukcust5"];
//Here I append single quotes before and after to each string if needed
const query = "SELECT * FROM table_name WHERE name = ?";
client.execute(query, arr, { prepare:true }, function (err, result) {
..//Code
};
What am I missing here? I want the query to be:
SELECT * FROM table_name WHERE name = each of the names in the array 'arr';
If name were a clustering key, then you could query with "in" and "allow filtering" like this:
select * from table_name where name in ('ukcust1','ukcust2','ukcust3') allow filtering
Assuming name is not a clustering key, you could use a clustering key (e.g., date_of_birth) if it made logical sense -- that is, if filtering by date made sense in relation to the name -- like this:
select * from table_name where date_of_birth in (1969, 1972) name in ('ukcust1','ukcust2','ukcust3') allow filtering
If you can't do either of those things, you will need to loop through the array with Javascript (e.g., foreach).
The correct input of the query parameters is an array of values. In this case, it would be an array of parameters containing a single item, that is an array of names.
const arr = ["ukcust1","ukcust2","ukcust5"];
const query = "SELECT * FROM table_name WHERE name = ?";
// Note the array containing a single item
const parameters = [ arr ];
client.execute(query, parameters, { prepare: true }, callback);
See more info in the documentation: https://docs.datastax.com/en/developer/nodejs-driver/3.5/faq/#how-can-i-use-a-list-of-values-with-the-in-operator-in-a-where-clause
Is it possible to use .QueryMultiple (or some other method) in Dapper, and use the results of each former query to be used in the where clause of the next query, without having to do each query individually, get the id, and then .Query again, get the id and so on.
For example,
string sqlString = #"select tableA_id from tableA where tableA_lastname = #lastname;
select tableB_id from tableB WHERE tableB_id = tableA_id";
db.QueryMultiple.(sqlString, new {lastname = "smith"});
Is something like this possible with Dapper or do I need a view or stored procedure to accomplish this? I can use multiple joins for one SQL statement, but in my real query there are 7 joins, and I didn't think I should return 7 objects.
Right now I'm just using object.
You can store every previous query in table parameter and then first perform select from the parameter and query for next, for example:
DECLARE #TableA AS Table(
tableA_id INT
-- ... all other columns you need..
)
INSERT #TableA
SELECT tableA_id
FROM tableA
WHERE tableA_lastname = #lastname
SELECT *
FROM #TableA
SELECT tableB_id
FROM tableB
JOIN tableA ON tableB_id = tableA_id
I've a problem with LINQ. Basically a third party database that I need to connect to is using the now depreciated text field (I can't change this) and I need to execute a distinct clause in my linq on results that contain this field.
I don't want to do a ToList() before executing the Distinct() as that will result in thousands of records coming back from the database that I don't require and will annoy the client as they get charged for bandwidth usage. I only need the first 15 distinct records.
Anyway query is below:
var query = (from s in db.tSearches
join sc in db.tSearchIndexes on s.GUID equals sc.CPSGUID
join a in db.tAttributes on sc.AttributeGUID equals a.GUID
where s.Notes != null && a.Attribute == "Featured"
select new FeaturedVacancy
{
Id = s.GUID,
DateOpened = s.DateOpened,
Notes = s.Notes
});
return query.Distinct().OrderByDescending(x => x.DateOpened);
I know I can do a subquery to do the same thing as above (tSearches contains unique records) but I'd rather a more straightfoward solution if available as I need to change a number of similar queries throughout the code to get this working.
No answers on how to do this so I went with my first suggestion and retrieved the unique records first from tSearch then constructed a subquery with the non unique records and filtered the search results by this subquery. Answer below:
var query = (from s in db.tSearches
where s.DateClosed == null && s.ConfidentialNotes != null
orderby s.DateOpened descending
select new FeaturedVacancy
{
Id = s.GUID,
Notes = s.ConfidentialNotes
});
/* Now filter by our 'Featured' attribute */
var subQuery = from sc in db.tSearchIndexes
join a in db.tAttributes on sc.AttributeGUID equals a.GUID
where a.Attribute == "Featured"
select sc.CPSGUID;
query = query.Where(x => subQuery.Contains(x.Id));
return query;
I want to perform a simple join on two tables (BusinessUnit and UserBusinessUnit), so I can get a list of all BusinessUnits allocated to a given user.
The first attempt works, but there's no override of Select which allows me to restrict the columns returned (I get all columns from both tables):
var db = new KensDB();
SqlQuery query = db.Select
.From<BusinessUnit>()
.InnerJoin<UserBusinessUnit>( BusinessUnitTable.IdColumn, UserBusinessUnitTable.BusinessUnitIdColumn )
.Where( BusinessUnitTable.RecordStatusColumn ).IsEqualTo( 1 )
.And( UserBusinessUnitTable.UserIdColumn ).IsEqualTo( userId );
The second attept allows the column name restriction, but the generated sql contains pluralised table names (?)
SqlQuery query = new Select( new string[] { BusinessUnitTable.IdColumn, BusinessUnitTable.NameColumn } )
.From<BusinessUnit>()
.InnerJoin<UserBusinessUnit>( BusinessUnitTable.IdColumn, UserBusinessUnitTable.BusinessUnitIdColumn )
.Where( BusinessUnitTable.RecordStatusColumn ).IsEqualTo( 1 )
.And( UserBusinessUnitTable.UserIdColumn ).IsEqualTo( userId );
Produces...
SELECT [BusinessUnits].[Id], [BusinessUnits].[Name]
FROM [BusinessUnits]
INNER JOIN [UserBusinessUnits]
ON [BusinessUnits].[Id] = [UserBusinessUnits].[BusinessUnitId]
WHERE [BusinessUnits].[RecordStatus] = #0
AND [UserBusinessUnits].[UserId] = #1
So, two questions:
- How do I restrict the columns returned in method 1?
- Why does method 2 pluralise the column names in the generated SQL (and can I get round this?)
I'm using 3.0.0.3...
So far my experience with 3.0.0.3 suggests that this is not possible yet with the query tool, although it is with version 2.
I think the preferred method (so far) with version 3 is to use a linq query with something like:
var busUnits = from b in BusinessUnit.All()
join u in UserBusinessUnit.All() on b.Id equals u.BusinessUnitId
select b;
I ran into the pluralized table names myself, but it was because I'd only re-run one template after making schema changes.
Once I re-ran all the templates, the plural table names went away.
Try re-running all 4 templates and see if that solves it for you.