Update tests and docs related to splitByString

dbms/tests/queries/0_stateless/01100_split_by_string.reference

@@ -5,3 +5,5 @@
 ['a','b','c','d','e']
 ['hello','world']
 ['gbye','bug']
+['']
+[]

dbms/tests/queries/0_stateless/01100_split_by_string.sql

@@ -4,3 +4,5 @@ select splitByString('ab', 'ababab');
 select splitByString('ababab', 'ababab');
 select splitByString('', 'abcde');
 select splitByString(', ', x) from (select arrayJoin(['hello, world', 'gbye, bug']) x);
+select splitByString('ab', '');
+select splitByString('', '');

docs/en/query_language/functions/splitting_merging_functions.md

@@ -1,11 +1,31 @@
 # Functions for splitting and merging strings and arrays
 
-## splitByChar(separator, s)
+## splitByChar
 
-Splits a string into substrings separated by 'separator'.'separator' must be a string constant consisting of exactly one character.
+Splits a string into substrings separated by a specified character. It uses a constant string `separator` which consisting of exactly one character.
-Returns an array of selected substrings. Empty substrings may be selected if the separator occurs at the beginning or end of the string, or if there are multiple consecutive separators.
 
-**Example:**
+**Syntax**
+
+```sql
+splitByChar(<separator>, <s>)
+```
+
+**Parameters**
+
+- `separator` — The separator which should contain exactly one character. [String](../../data_types/string.md).
+- `s` — The string to split. [String](../../data_types/string.md).
+
+**Returned value(s)**
+
+Returns an array of selected substrings. Empty substrings may be selected when:
+
+* A separator occurs at the beginning or end of the string;
+* There are multiple consecutive separators;
+* The original string `s` is empty.
+
+Type: [Array](../../data_types/array.md) of [String](../../data_types/string.md).
+
+**Example**
 
 ```sql
 SELECT splitByChar(',', '1,2,3,abcde')
@@ -16,11 +36,32 @@ SELECT splitByChar(',', '1,2,3,abcde')
 └─────────────────────────────────┘
 ```
 
-## splitByString(separator, s)
+## splitByString
 
-The same as above, but it uses a string of multiple characters as the separator. If the string is empty, it will split the string into an array of single characters.
+Splits a string into substrings separated by a string. It uses a constant string `separator` of multiple characters as the separator. If the string `separator` is empty, it will split the string `s` into an array of single characters.
 
-**Example:**
+**Syntax**
+
+```sql
+splitByString(<separator>, <s>)
+```
+
+**Parameters**
+
+- `separator` — The separator. [String](../../data_types/string.md).
+- `s` — The string to split. [String](../../data_types/string.md).
+
+**Returned value(s)**
+
+Returns an array of selected substrings. Empty substrings may be selected when:
+
+* A non-empty separator occurs at the beginning or end of the string;
+* There are multiple consecutive non-empty separators;
+* The original string `s` is empty while the separator is not empty.
+
+Type: [Array](../../data_types/array.md) of [String](../../data_types/string.md).
+
+**Example**
 
 ```sql
 SELECT splitByString(', ', '1, 2 3, 4,5, abcde')
@@ -49,7 +90,7 @@ Returns the string.
 
 Selects substrings of consecutive bytes from the ranges a-z and A-Z.Returns an array of substrings.
 
-**Example:**
+**Example**
 
 ```sql
 SELECT alphaTokens('abca1abc')