Wire up SELECT DISTINCT

[corylanou]

Distinct with strings

the raw data

> select * from names
name: names
-----------
time                    first   last
2015-05-01T00:00:00Z    suzie   smith
2015-05-01T08:00:00Z    frank   smith
2015-05-01T16:00:00Z    jonny   jones

distinct with no where or group by

> select distinct(first) from names
name: names
-----------
time                    distinct
1970-01-01T00:00:00Z    [frank jonny suzie]

> select distinct(last) from names
name: names
-----------
time                    distinct
1970-01-01T00:00:00Z    [jones smith]

Distinct with no fields will currently return an error (not supported)

> select distinct() from names
ERR: error parsing query: distinct function requires at least one argument

Distinct with more than one field will currently return an error (not supported)

> select distinct(first, last) from names
ERR: error parsing query: distinct function can only have one argument

Distinct with a group by and no where clause will err out (like all aggregate functions should)

> select distinct(last) from names group by time(1h)
ERR: error parsing query: aggregate functions with GROUP BY time require a WHERE time clause

Distinct with group by and where should bucket values appropriatly

> select distinct(last) from names where time >= '2015-05-01T00:00:00Z' and time <= '2015-05-01T16:00:00Z' group by time(12h)
name: names
-----------
time                    distinct
2015-05-01T00:00:00Z    [smith]
2015-05-01T12:00:00Z    [jones]

> select distinct(first) from names where time >= '2015-05-01T00:00:00Z' and time <= '2015-05-01T16:00:00Z' group by time(12h)
name: names
-----------
time                    distinct
2015-05-01T00:00:00Z    [frank suzie]
2015-05-01T12:00:00Z    [jonny]

Distinct with numeric data

the raw data

> select * from cpu
name: cpu
---------
time                    value
2015-05-01T00:00:00Z    1.1
2015-05-01T08:00:00Z    1.2
2015-05-01T16:00:00Z    1.3
2015-05-02T00:00:00Z    2.1
2015-05-02T08:00:00Z    2.2
2015-05-02T16:00:00Z    2.3
2015-05-03T00:00:00Z    3.1
2015-05-03T08:00:00Z    3.2
2015-05-03T16:00:00Z    3.3
2015-05-04T00:00:00Z    4.1
2015-05-04T08:00:00Z    4.2
2015-05-04T16:00:00Z    4.3

distinct with no where or group by

select distinct(value) from cpu
name: cpu
---------
time                    distinct
1970-01-01T00:00:00Z    [1.1 1.2 1.3 2.1 2.2 2.3 3.1 3.2 3.3 4.1 4.2 4.3]

distinct with different groupings

> select distinct(value) from cpu where time >= '2015-05-01T00:00:00Z' and time <= '2015-05-04T00:00:00Z' group by time(12h)
name: cpu
---------
time                    distinct
2015-05-01T00:00:00Z    [1.1 1.2]
2015-05-01T12:00:00Z    [1.3]
2015-05-02T00:00:00Z    [2.1 2.2]
2015-05-02T12:00:00Z    [2.3]
2015-05-03T00:00:00Z    [3.1 3.2]
2015-05-03T12:00:00Z    [3.3]
2015-05-04T00:00:00Z    [4.1 4.2]

> select distinct(value) from cpu where time >= '2015-05-01T00:00:00Z' and time <= '2015-05-04T00:00:00Z' group by time(1d)
name: cpu
---------
time                    distinct
2015-05-01T00:00:00Z    [1.1 1.2 1.3]
2015-05-02T00:00:00Z    [2.1 2.2 2.3]
2015-05-03T00:00:00Z    [3.1 3.2 3.3]
2015-05-04T00:00:00Z    [4.1 4.2 4.3]

[pauldix]

Looks good so far. Although your sort doesn't handle a bool field :).

Curious how you're going to handle it when they pass in a tag name and a WHERE time clause ;)

[corylanou]

Fixes #1815

[dgnorton]

I would simplify this method to look like this... https://gist.github.com/dgnorton/3125e459045a5cedc948

[dgnorton]

I agree with @jwilder that the Validate* functions should be converted to private...even the pre-existing ones. Including the root Validate function, which is only called at the end of parseSelectStatement.

[dgnorton]

Need to add more tests for the validation code. e.g. select count(distinct(too, many, arguments)) passes.

[corylanou]

Addressed all items. Will address select count(distinct(too, many, arguments)) tests in #1891 as it has more edge cases to deal with including this one.

[jwilder]

LGTM 👍

[pauldix]

Looks good. One thing left over from this is to handle when the user passes in a tag key to distinct. Logged #2612