I've been trying to run a subquery in GCP BigQuery but it's giving an error. This is part of the Google Data Analytics course. The intent is to "compare the number of bikes available at the station with the average number of bikes available"
The dataset is bigquery-public-data with 2 tables namely, citibike_stations and citibike_trips. The only table used is the citibike_stations.
The following is my query and subquery:
SELECT station_id, num_bikes_available (SELECT AVG(num_bikes_available) FROM bigquery-public-data.new_york_citibike.citibike_stations) AS avg_num_bikes_available FROM bigquery-public-data.new_york_citibike.citibike_stations ;
You are simply missing a comma. See the comma highlighted on line 3.
You are using the subquery as a column in the outer SELECT, so you simply need a comma separating all the output columns.
Related
So I'm kinda new to SQL and been following some tutorial courses online.
I want to compare the num_bikes_available at a station to the average num_bikes_available.
My question is why cant it just show the average using the OUTER SELECT clause? Why do it need to be done using SUBQUERY? My Answer. Tutorial Answer.
Query SELECT AVG(num_bikes_available) FROM citibike_stations will return a single row with average calculated over all rows.
Now, if you add station_id like SELECT station_id, AVG(num_bikes_available) FROM citibike_stations, this is also supposed to return a single row, but BigQuery does not know which exactly station_id value do you need. Therefore you see that error.
BigQuery can show average for every distinct station_id value it finds, but to do that it needs the GROUP BY clause like SELECT station_id, AVG(num_bikes_available) FROM citibike_stations GROUP BY station_id.
I have a query
SELECT COUNT(*) AS "CNT",
imei
FROM devices
which executes just fine. I want to further restrict the query with a WHERE statement. The (humanly) logical next step is to modify the query followingly:
SELECT COUNT(*) AS "CNT",
imei
FROM devices
WHERE CNT > 1
However, this results in a error message ORA-00904: "CNT": invalid identifier. For some reason, wrapping the query in another query produces the desired result:
SELECT *
FROM (SELECT COUNT(*) AS "CNT",
imei
FROM devices
GROUP BY imei)
WHERE CNT > 1
Why does Oracle not recognize the alias "CNT" in the second query?
Because the documentation says it won't:
Specify an alias for the column
expression. Oracle Database will use
this alias in the column heading of
the result set. The AS keyword is
optional. The alias effectively
renames the select list item for the
duration of the query. The alias can
be used in the order_by_clause but not
other clauses in the query.
However, when you have an inner select, that is like creating an inline view where the column aliases take effect, so you are able to use that in the outer level.
The simple answer is that the AS clause defines what the column will be called in the result, which is a different scope than the query itself.
In your example, using the HAVING clause would work best:
SELECT COUNT(*) AS "CNT",
imei
FROM devices
GROUP BY imei
HAVING COUNT(*) > 1
To summarize, this little gem explains:
10 Easy Steps to a Complete Understanding of SQL
A common source of confusion is the simple fact that SQL syntax
elements are not ordered in the way they are executed. The lexical
ordering is:
SELECT [ DISTINCT ]
FROM
WHERE
GROUP BY
HAVING
UNION
ORDER BY
For simplicity, not all SQL clauses are listed. This lexical ordering
differs fundamentally from the logical order, i.e. from the order of
execution:
FROM
WHERE
GROUP BY
HAVING
SELECT
DISTINCT
UNION
ORDER BY
As a consequence, anything that you label using "AS" will only be available once the WHERE, HAVING and GROUP BY have already been performed.
I would imagine because the alias is not assigned to the result column until after the WHERE clause has been processed and the data generated. Is Oracle different from other DBMSs in this behaviour?
I have a table BAR_DATA with two fields: LongDate, Time. Both are long integers. No Access Date/Time involved here.
For each distinct LongDate value there are hundreds of records, each with Time value which may be distinct or duplicate within that LongDate.
I need to create an SQL statement that will group by LongDate and give me a count of distinct Times within each LongDate.
The following SQL statement, (built by an Acess query) does NOT work (some LongDates are omitted):
Query A
SELECT DISTINCT BAR_DATA.LongDate, Count(BAR_DATA.Time) AS CountOfTime
FROM BAR_DATA
GROUP BY BAR_DATA.LongDate
HAVING (((Count(BAR_DATA.Time))<>390 And (Count(BAR_DATA.Time))<>210));
However, if I use Query B to reference Query DistinctDateTime, it does work:
Query B
SELECT DistinctDateTime.LongDate, Count(DistinctDateTime.Time) AS CountOfTime
FROM DistinctDateTime
GROUP BY DistinctDateTime.LongDate
HAVING (((Count(DistinctDateTime.Time))<>390 And (Count(DistinctDateTime.Time))<>210));
Query DistinctDateTime
SELECT DISTINCT BAR_DATA.LongDate, BAR_DATA.Time
FROM BAR_DATA;
My problem:
I need to get Query B and Query DistinctDateTime wrapped into a single SQL statement so I can paste it into a VBA function. I presume there
is some subquery techniques, but I have failed at every attempt, and find no pertinent example.
Any help will be greatly appreciated. Thanks!
Subquery your distinct table inside and perform your aggregates outside until you get the desired result:
SELECT DistinctDateTime.LongDate, Count(DistinctDateTime.Time) AS CountOfTime
FROM
(
SELECT DISTINCT BAR_DATA.LongDate, BAR_DATA.Time
FROM BAR_DATA
) AS DistinctDateTime
GROUP BY DistinctDateTime.LongDate
HAVING (((Count(DistinctDateTime.Time))<>390 And (Count(DistinctDateTime.Time))<>210));
I am trying to use pivot to display my information. I want to use a subquery to select the columns in the report:
select * from
(select continent, country, population
from continents, countries
where continents.id=countries.id
)
pivot (sum(population) for country in (select distinct country from countries)
I keep getting an error when I try to use a subquery to get the list of countries.
I tried using pivot XML but that didn't work either since it returned meaningless xml code.
I want to see the actual numbers!
You can't use result of subquery in PIVOT clause as columns need to be defined statically. But you can generate dynamic SQL using results of your subquery and then execute it via execute immediate.
I have a query
SELECT COUNT(*) AS "CNT",
imei
FROM devices
which executes just fine. I want to further restrict the query with a WHERE statement. The (humanly) logical next step is to modify the query followingly:
SELECT COUNT(*) AS "CNT",
imei
FROM devices
WHERE CNT > 1
However, this results in a error message ORA-00904: "CNT": invalid identifier. For some reason, wrapping the query in another query produces the desired result:
SELECT *
FROM (SELECT COUNT(*) AS "CNT",
imei
FROM devices
GROUP BY imei)
WHERE CNT > 1
Why does Oracle not recognize the alias "CNT" in the second query?
Because the documentation says it won't:
Specify an alias for the column
expression. Oracle Database will use
this alias in the column heading of
the result set. The AS keyword is
optional. The alias effectively
renames the select list item for the
duration of the query. The alias can
be used in the order_by_clause but not
other clauses in the query.
However, when you have an inner select, that is like creating an inline view where the column aliases take effect, so you are able to use that in the outer level.
The simple answer is that the AS clause defines what the column will be called in the result, which is a different scope than the query itself.
In your example, using the HAVING clause would work best:
SELECT COUNT(*) AS "CNT",
imei
FROM devices
GROUP BY imei
HAVING COUNT(*) > 1
To summarize, this little gem explains:
10 Easy Steps to a Complete Understanding of SQL
A common source of confusion is the simple fact that SQL syntax
elements are not ordered in the way they are executed. The lexical
ordering is:
SELECT [ DISTINCT ]
FROM
WHERE
GROUP BY
HAVING
UNION
ORDER BY
For simplicity, not all SQL clauses are listed. This lexical ordering
differs fundamentally from the logical order, i.e. from the order of
execution:
FROM
WHERE
GROUP BY
HAVING
SELECT
DISTINCT
UNION
ORDER BY
As a consequence, anything that you label using "AS" will only be available once the WHERE, HAVING and GROUP BY have already been performed.
I would imagine because the alias is not assigned to the result column until after the WHERE clause has been processed and the data generated. Is Oracle different from other DBMSs in this behaviour?