**Description**: The concatenation result of two or more strings, the number of strings to be concatenated is at least 2 and at most 8
**Return value type**: If all input strings are BINARY type, the result is BINARY type too. If any one of input strings is NCHAR type, then the result is NCHAR.
**Return value type**: If all input strings are VARCHAR type, the result is VARCHAR type too. If any one of input strings is NCHAR type, then the result is NCHAR.
**Applicable data types**: BINARY, NCHAR. Can't be used on tag columns. At least 2 input strings are requird, and at most 8 input strings are allowed.
**Applicable data types**: VARCHAR, NCHAR. Can't be used on tag columns. At least 2 input strings are requird, and at most 8 input strings are allowed.
**Applicable table types**: table, STable
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@@ -317,9 +295,9 @@ SELECT CONCAT_WS(separator, str1|column1, str2|column2, ...) FROM { tb_name | st
**Description**: The concatenation result of two or more strings with separator, the number of strings to be concatenated is at least 3 and at most 9
**Return value type**: If all input strings are BINARY type, the result is BINARY type too. If any one of input strings is NCHAR type, then the result is NCHAR.
**Return value type**: If all input strings are VARCHAR type, the result is VARCHAR type too. If any one of input strings is NCHAR type, then the result is NCHAR.
**Applicable data types**: BINARY, NCHAR. Can't be used on tag columns. At least 3 input strings are requird, and at most 9 input strings are allowed.
**Applicable data types**: VARCHAR, NCHAR. Can't be used on tag columns. At least 3 input strings are requird, and at most 9 input strings are allowed.
**Description**: It's used for type casting. The input parameter `expression` can be data columns, constants, scalar functions or arithmetic between them. Can't be used with tags, and can only be used in `select` clause.
**Description**: It's used for type casting. The input parameter `expression` can be data columns, constants, scalar functions or arithmetic between them.
**Return value type**: The type specified by parameter `type_name`
**Applicable data types**:
- Parameter `expression` can be any data type except for JSON, more specifically it can be any of BOOL/TINYINT/SMALLINT/INT/BIGINT/FLOAT/DOUBLE/BINARY(M)/TIMESTAMP/NCHAR(M)/TINYINT UNSIGNED/SMALLINT UNSIGNED/INT UNSIGNED/BIGINT UNSIGNED
- The output data type specified by `type_name` can only be one of BIGINT/BINARY(N)/TIMESTAMP/NCHAR(N)/BIGINT UNSIGNED
- Parameter `expression` can be any data type except for JSON
- The output data type specified by `type_name` can only be one of BIGINT/VARCHAR(N)/TIMESTAMP/NCHAR(N)/BIGINT UNSIGNED
**More explanations**:
- Error will be reported for unsupported type casting
- NULL will be returned if the input value is NULL
- Some values of some supported data types may not be casted, below are known issues:
1）When casting BINARY/NCHAR to BIGINT/BIGINT UNSIGNED, some characters may be treated as illegal, for example "a" may be converted to 0.
1）When casting VARCHAR/NCHAR to BIGINT/BIGINT UNSIGNED, some characters may be treated as illegal, for example "a" may be converted to 0.
2）There may be overflow when casting singed integer or TIMESTAMP to unsigned BIGINT
3）There may be overflow when casting unsigned BIGINT to BIGINT
4）There may be overflow when casting FLOAT/DOUBLE to BIGINT or UNSIGNED BIGINT
SELECT MODE(field_name) FROM tb_name [WHERE clause];
```
**Description**:The value which has the highest frequency of occurrence. NULL is returned if there are multiple values which have highest frequency of occurrence. It can't be used on timestamp column or tags.
**Description**:The value which has the highest frequency of occurrence. NULL is returned if there are multiple values which have highest frequency of occurrence. It can't be used on timestamp column.
**Return value type**:Same as the data type of the column being operated upon
