Forced Conversion Functions

1

CAST()

Supported

• In GaussDB, CAST(expr AS CHAR[(N)] charset_info or CAST(expr AS NCHAR[(N)]) cannot be used to convert character sets.
• In GaussDB, you can use CAST(expr AS FLOAT[(p)]) or CAST(expr AS DOUBLE) to convert an expression to the one of the floating-point type. MySQL 5.7 does not support this conversion.
• In GaussDB, CAST(expr AS JSON) cannot be used to convert expressions to JSON.
• In the CAST nested subquery scenario, if the subquery statement returns the FLOAT type, an accurate value is returned in GaussDB while a distorted value is returned in MySQL 5.7. The same rule applies to the BINARY function implemented using CAST.

  --GaussDB
  m_db=# CREATE TABLE sub_query_table (myfloat float) DISTRIBUTE BY REPLICATION;
  CREATE TABLE
  m_db=# INSERT INTO sub_query_table (myfloat) VALUES (1.23);
  INSERT 0 1
  m_db=# SELECT BINARY (select MyFloat from sub_query_table ) from sub_query_table;
   binary 
  --------
   1.23
  (1 row)
  m_db=# SELECT CAST((select MyFloat from sub_query_table ) AS char);
   cast 
  ------
   1.23
  (1 row)
  --Mysql 5.7
  mysql> CREATE TABLE sub_query_table (myfloat float);
  Query OK, 0 rows affected (0.02 sec)
  mysql> INSERT INTO sub_query_table (myfloat) VALUES (1.23);
  Query OK, 1 row affected (0.00 sec)
  mysql> SELECT BINARY (select MyFloat from sub_query_table ) from sub_query_table;
  +-----------------------------------------------+
  | BINARY (select MyFloat from sub_query_table ) |
  +-----------------------------------------------+
  | 1.2300000190734863                            |
  +-----------------------------------------------+
  1 row in set (0.00 sec)
  mysql> SELECT CAST((select MyFloat from sub_query_table ) AS char);
  +------------------------------------------------------+
  | CAST((select MyFloat from sub_query_table ) AS char) |
  +------------------------------------------------------+
  | 1.2300000190734863                                   |
  +------------------------------------------------------+
  1 row in set (0.00 sec)

2

CONVERT()

Supported

• In GaussDB, CONVERT(expr, CHAR[(N)] charset_info or CAST(expr, NCHAR[(N)]) cannot be used to convert character sets.
• In GaussDB, you can use CONVERT(expr, FLOAT[(p)]) or CONVERT(expr, DOUBLE) to convert an expression to the one of the floating-point type. MySQL 5.7 does not support this conversion.

• In GaussDB, CONVERT(expr, JSON) cannot be used to convert expressions to JSON.