Merge pull request #4 from Oreoxmt/review_seq_func

Sequence functions: refine wording

functions-and-operators/sequence-functions.md

@@ -7,35 +7,33 @@ summary: This document introduces sequence functions supported in TiDB.
 
 Sequence functions in TiDB are used to return or set values of sequence objects created using the [`CREATE SEQUENCE`](/sql-statements/sql-statement-create-sequence.md) statement.
 
-| Function name | Feature description |
+| Function name | Description |
 | :-------------- | :------------------------------------- |
-| [`NEXTVAL()`](#nextval) | Returns the next value of a sequence |
-| [`NEXT VALUE FOR`](#next-value-for) | Returns the next value of a sequence |
-| [`SETVAL()`](#setval) | Sets the current value of a sequence |
-| [`LASTVAL()`](#lastval) | Returns the last used value of a sequence |
+| [`NEXTVAL()`](#nextval) | Returns the next value of a sequence. |
+| [`NEXT VALUE FOR`](#next-value-for) | Returns the next value of a sequence (alias for `NEXTVAL()`). |
+| [`SETVAL()`](#setval) | Sets the current value of a sequence. |
+| [`LASTVAL()`](#lastval) | Returns the last used value of a sequence in the current session. |
 
 ## `NEXTVAL()`
 
-The `NEXTVAL()` functions returns the next value from the sequence
+The `NEXTVAL()` function returns the next value of a sequence.
 
 Example:
 
-We create a sequence called `s1`.
+Create a sequence named `s1`:
 
 ```sql
 CREATE SEQUENCE s1;
 ```
 
-```
-Query OK, 0 rows affected (0.01 sec)
-```
-
-Then we request the next value from `s1`.
+Get the next value from `s1`:
 
 ```sql
 SELECT NEXTVAL(s1);
 ```
 
+The output is as follows:
+
 ```
 +-------------+
 | NEXTVAL(s1) |
@@ -47,12 +45,18 @@ SELECT NEXTVAL(s1);
 
 ## `NEXT VALUE FOR`
 
-An alias for [`NEXTVAL()`](#nextval)
+The `NEXT VALUE FOR` function is an alias for [`NEXTVAL()`](#nextval).
+
+Example:
+
+Get the next value from `s1` using `NEXTVAL()`:
 
 ```sql
 SELECT NEXTVAL(s1);
 ```
 
+The output is as follows:
+
 ```
 +-------------+
 | NEXTVAL(s1) |
@@ -62,10 +66,14 @@ SELECT NEXTVAL(s1);
 1 row in set (0.00 sec)
 ```
 
+Get the next value from `s1` using `NEXT VALUE FOR`:
+
 ```sql
 SELECT NEXT VALUE FOR s1;
 ```
 
+The output is as follows:
+
 ```
 +-------------------+
 | NEXT VALUE FOR s1 |
@@ -77,14 +85,18 @@ SELECT NEXT VALUE FOR s1;
 
 ## `SETVAL()`
 
-The `SETVAL(n)` function can be use to set a sequence to a specific value.
+The `SETVAL(n)` function sets the current value of a sequence.
 
-We request the next value from `s1`.
+Example:
+
+Get the next value from `s1`:
 
 ```sql
 SELECT NEXTVAL(s1);
 ```
 
+The output is as follows:
+
 ```
 +-------------+
 | NEXTVAL(s1) |
@@ -94,12 +106,14 @@ SELECT NEXTVAL(s1);
 1 row in set (0.00 sec)
 ```
 
-Now we set the value to `10`.
+Set the current value of `s1` to `10`:
 
 ```sql
 SELECT SETVAL(s1, 10);
 ```
 
+The output is as follows:
+
 ```
 +----------------+
 | SETVAL(s1, 10) |
@@ -109,12 +123,14 @@ SELECT SETVAL(s1, 10);
 1 row in set (0.00 sec)
 ```
 
-And now we can see that the next value (the value after `10`) is `11`.
+Verify the next value after setting it to `10`:
 
 ```sql
 SELECT NEXTVAL(s1);
 ```
 
+The output is as follows:
+
 ```
 +-------------+
 | NEXTVAL(s1) |
@@ -126,12 +142,18 @@ SELECT NEXTVAL(s1);
 
 ## `LASTVAL()`
 
-The `LASTVAL()` function returns the last value that was generated by the sequence in **this session**.
+The `LASTVAL()` function returns the last value generated by the sequence **in the current session**.
+
+Example:
+
+Get the next value from `s1`:
 
 ```sql
 SELECT LASTVAL(s1);
 ```
 
+The output is as follows:
+
 ```
 +-------------+
 | LASTVAL(s1) |