PPL fieldsummary command

docs/ppl-lang/PPL-Example-Commands.md

@@ -33,6 +33,12 @@ _- **Limitation: new field added by eval command with a function cannot be dropp
 - `source = table | eval b1 = b + 1 | fields - b1,c` (Field `b1` cannot be dropped caused by SPARK-49782)
 - `source = table | eval b1 = lower(b) | fields - b1,c` (Field `b1` cannot be dropped caused by SPARK-49782)
 
+**Field-Summary**
+[See additional command details](ppl-fieldsummary-command.md)
+- `source = t | fieldsummary includefields=status_code nulls=false`
+- `source = t | fieldsummary includefields= id, status_code, request_path nulls=true`
+- `source = t | where status_code != 200 | fieldsummary includefields= status_code nulls=true`
+
 **Nested-Fields**
 - `source = catalog.schema.table1, catalog.schema.table2 | fields A.nested1, B.nested1`
 - `source = catalog.table | where struct_col2.field1.subfield > 'valueA' | sort int_col | fields  int_col, struct_col.field1.subfield, struct_col2.field1.subfield`

docs/ppl-lang/ppl-fieldsummary-command.md

@@ -0,0 +1,83 @@
+## PPL `fieldsummary` command
+
+**Description**
+Using `fieldsummary` command to :
+ - Calculate basic statistics for each field (count, distinct count, min, max, avg, stddev, mean )
+ - Determine the data type of each field
+
+**Syntax**
+
+`... | fieldsummary <field-list> (nulls=true/false)`
+
+* command accepts any preceding pipe before the terminal `fieldsummary` command and will take them into account. 
+* `includefields`: list of all the columns to be collected with statistics into a unified result set
+* `nulls`: optional; if the true, include the null values in the aggregation calculations (replace null with zero for numeric values)
+
+### Example 1: 
+
+PPL query:
+
+    os> source = t | where status_code != 200 | fieldsummary includefields= status_code nulls=true
+    +------------------+-------------+------------+------------+------------+------------+------------+------------+----------------|
+    | Fiels            | COUNT       | COUNT_DISTINCT    |  MIN  |  MAX   |  AVG   |  MEAN   |        STDDEV       | NUlls | TYPEOF |
+    |------------------+-------------+------------+------------+------------+------------+------------+------------+----------------|
+    | "status_code"    |      2      |         2         | 301   |   403  |  352.0 |  352.0  |  72.12489168102785  |  0    | "int"  |
+    +------------------+-------------+------------+------------+------------+------------+------------+------------+----------------|
+
+### Example 2: 
+
+PPL query:
+
+    os> source = t | fieldsummary includefields= id, status_code, request_path nulls=true
+    +------------------+-------------+------------+------------+------------+------------+------------+------------+----------------|
+    | Fiels            | COUNT       | COUNT_DISTINCT    |  MIN  |  MAX   |  AVG   |  MEAN   |        STDDEV       | NUlls | TYPEOF |
+    |------------------+-------------+------------+------------+------------+------------+------------+------------+----------------|
+    |       "id"       |      6      |         6         | 1     |   6    |  3.5   |   3.5  |  1.8708286933869707  |  0    | "int"  |
+    +------------------+-------------+------------+------------+------------+------------+------------+------------+----------------|
+    | "status_code"    |      4      |         3         | 200   |   403  |  184.0 |  184.0  |  161.16699413961905 |  2    | "int"  |
+    +------------------+-------------+------------+------------+------------+------------+------------+------------+----------------|
+    | "request_path"   |      2      |         2         | /about| /home  |  0.0    |  0.0     |      0              |  2    |"string"|
+    +------------------+-------------+------------+------------+------------+------------+------------+------------+----------------|
+
+### Additional Info
+The actual query is translated into the following SQL-like statement:
+
+```sql
+     SELECT
+         id AS Field,
+         COUNT(id) AS COUNT,
+        COUNT(DISTINCT id) AS COUNT_DISTINCT,
+        MIN(id) AS MIN,
+        MAX(id) AS MAX,
+        AVG(id) AS AVG,
+        MEAN(id) AS MEAN,
+        STDDEV(id) AS STDDEV,
+        (COUNT(1) - COUNT(id)) AS Nulls,
+        TYPEOF(id) AS TYPEOF
+     FROM
+         t
+     GROUP BY
+         TYPEOF(status_code), status_code;
+UNION
+    SELECT
+        status_code AS Field,
+        COUNT(status_code) AS COUNT,
+        COUNT(DISTINCT status_code) AS COUNT_DISTINCT,
+        MIN(status_code) AS MIN,
+        MAX(status_code) AS MAX,
+        AVG(status_code) AS AVG,
+        MEAN(status_code) AS MEAN,
+        STDDEV(status_code) AS STDDEV,
+        (COUNT(1) - COUNT(status_code)) AS Nulls,
+        TYPEOF(status_code) AS TYPEOF
+    FROM
+        t
+    GROUP BY
+        TYPEOF(status_code), status_code;
+```
+For each such columns (id, status_code) there will be a unique statement and all the fields will be presented togather in the result using a UNION operator
+
+
+### Limitation: 
+ - `topvalues` option was removed from this command due the possible performance impact of such sub-query. As an alternative one can use the `top` command directly as shown [here](ppl-top-command.md). 
+