added window functions

Author: ashwinkumar12345

docs/sql/delete.md

@@ -2,7 +2,7 @@
 layout: default
 title: Delete
 parent: SQL
-nav_order: 11
+nav_order: 12
 ---
 
 

docs/sql/endpoints.md

@@ -2,7 +2,7 @@
 layout: default
 title: Endpoint
 parent: SQL
-nav_order: 12
+nav_order: 13
 ---
 
 

docs/sql/functions.md

@@ -131,3 +131,54 @@ Function | Specification | Example
 if | `if(boolean, es_type, es_type) -> es_type` | `SELECT if(false, 0, 1) FROM my-index LIMIT 1`, `SELECT if(true, 0, 1) FROM my-index LIMIT 1`
 ifnull | `ifnull(es_type, es_type) -> es_type` | `SELECT ifnull('hello', 1) FROM my-index LIMIT 1`, `SELECT ifnull(null, 1) FROM my-index LIMIT 1`
 isnull | `isnull(es_type) -> integer` | `SELECT isnull(null) FROM my-index LIMIT 1`, `SELECT isnull(1) FROM my-index LIMIT 1`
+
+## Ranking
+
+Ranking functions assign an incremental rank to each row in the frame.
+
+If the ranking function is not used with the window definition that defines the order of data rows, the result is undetermined.
+
+### ROW_NUMBER
+
+`ROW_NUMBER` assigns a row number to data rows in a random order. As a special case, the row number is always increased by 1 regardless of the fields specified in the `ORDER BY` list.
+
+```sql
+od> SELECT gender, balance, ROW_NUMBER() OVER(PARTITION BY gender ORDER BY balance) AS num FROM accounts;
+```
+
+| gender | balance | num
+:--- | :---
+| F        | 32838     | 1     
+| M        | 4180      | 1     
+| M        | 5686      | 2     
+| M        | 39225     | 3     
+
+### RANK
+
+The `RANK` function assigns a rank to each row. For rows that have the same values for fields specified in the `ORDER BY` list, the same rank is assigned. If this is the case, the next few ranks is skipped depending on the number of ties.
+
+```sql
+od> SELECT gender, RANK() OVER(ORDER BY gender DESC) AS rnk FROM accounts;
+```
+
+| gender | rank
+:--- | :---
+| M        | 1     
+| M        | 1     
+| M        | 1     
+| F        | 4     
+
+### DENSE_RANK
+
+Similar to the `RANK` function, `DENSE_RANK` also assigns a rank to each row. The difference is there is no gap between the ranks.
+
+```sql
+SELECT gender, DENSE_RANK() OVER(ORDER BY gender DESC) AS rnk FROM accounts;
+```
+
+| gender | rank
+:--- | :---
+| M        | 1     
+| M        | 1     
+| M        | 1     
+| F        | 2   

docs/sql/limitation.md

@@ -2,7 +2,7 @@
 layout: default
 title: Limitations
 parent: SQL
-nav_order: 17
+nav_order: 18
 ---
 
 # Limitations

docs/sql/monitoring.md

@@ -2,7 +2,7 @@
 layout: default
 title: Monitoring
 parent: SQL
-nav_order: 14
+nav_order: 15
 ---
 
 # Monitoring

docs/sql/protocol.md

@@ -2,7 +2,7 @@
 layout: default
 title: Protocol
 parent: SQL
-nav_order: 13
+nav_order: 14
 ---
 
 # Protocol

docs/sql/settings.md

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 layout: default
 title: Settings
 parent: SQL
-nav_order: 15
+nav_order: 16
 ---
 
 # Settings

docs/sql/troubleshoot.md

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 layout: default
 title: Troubleshooting
 parent: SQL
-nav_order: 16
+nav_order: 17
 ---
 
 # Troubleshooting

docs/sql/window.md

@@ -0,0 +1,86 @@
+---
+layout: default
+title: Window Functions
+parent: SQL
+nav_order: 11
+---
+
+# Window Functions
+
+A window function performs a calculation across a frame of data rows around the current row and finds a result for each row.
+
+`PARTITION` and `ORDER` define the frame of data over which the calculations are made.
+
+You can use window functions in following three categories:
+
+1. Aggregate Functions: `COUNT()`, `MIN()`, `MAX()`, `AVG()`, and `SUM()`.
+2. Ranking Functions: `ROW_NUMBER()`, `RANK()`, `DENSE_RANK()`, `PERCENT_RANK()`, and `NTILE()`.
+3. Analytic Functions: `CUME_DIST()`, `LAG()`, and `LEAD()`.
+
+The syntax of a window function is as follows:
+
+```sql
+function_name (expression [, expression...])
+  OVER (
+    PARTITION BY expression [, expression...]
+    ORDER BY expression [ASC | DESC] [, ...]
+    )
+```
+
+The `PARTITION BY` and `ORDER BY` clauses are optional.
+{.. note}
+
+
+## Ranking Functions
+
+Ranking functions assign an incremental rank to each row in the frame.
+The increase in rank number is based on the ranking function implementation, though the rank is mostly determined by field values in the `ORDER BY` list. If the `PARTITION BY` clause is present, the state of ranking functions (incremental rank number maintained) is reset.
+
+If the ranking functions is not used with the window definition that defines the order of data rows, the result is undetermined.
+
+In this case, `ROW_NUMBER` assigns row number to data rows in random order. `RANK` and `DENSE_RANK` always assign a rank of 1 to each row.
+
+### ROW_NUMBER
+
+The row number function assigns a row number to each row. As a special case, the row number is always increased by 1 regardless of the fields specified in the `ORDER BY` list.
+
+```sql
+od> SELECT gender, balance, ROW_NUMBER() OVER(PARTITION BY gender ORDER BY balance) AS num FROM accounts;
+```
+
+| gender | balance | num
+:--- | :---
+| F        | 32838     | 1     
+| M        | 4180      | 1     
+| M        | 5686      | 2     
+| M        | 39225     | 3     
+
+### RANK
+
+The `RANK` function assigns a rank to each row. For rows that have the same values for fields specified in the `ORDER BY` list, the same rank is assigned. If this is the case, the next few ranks is skipped depending on the number of ties.
+
+```sql
+od> SELECT gender, RANK() OVER(ORDER BY gender DESC) AS rnk FROM accounts;
+```
+
+| gender | rank
+:--- | :---
+| M        | 1     
+| M        | 1     
+| M        | 1     
+| F        | 4     
+
+### DENSE_RANK
+
+Similar to the `RANK` function, `DENSE_RANK` also assigns a rank to each row. The difference is there is no gap between the ranks.
+
+```sql
+SELECT gender, DENSE_RANK() OVER(ORDER BY gender DESC) AS rnk FROM accounts;
+```
+
+| gender | rank
+:--- | :---
+| M        | 1     
+| M        | 1     
+| M        | 1     
+| F        | 2