Add helper classes for ST_FIELD_INFO

ST_FIELD_INFO is used to define INFORMATION_SCHEMA columns. A typical INFORMATION_SCHEMA table definition looks like this:

ST_FIELD_INFO schema_fields_info[]=

{

  {"CATALOG_NAME", FN_REFLEN, MYSQL_TYPE_STRING, 0, 0, 0, SKIP_OPEN_TABLE},

  {"SCHEMA_NAME", NAME_CHAR_LEN, MYSQL_TYPE_STRING, 0, 0, "Database",

   SKIP_OPEN_TABLE},

  {"DEFAULT_CHARACTER_SET_NAME", MY_CS_NAME_SIZE, MYSQL_TYPE_STRING, 0, 0, 0,

   SKIP_OPEN_TABLE},

  {"DEFAULT_COLLATION_NAME", MY_CS_NAME_SIZE, MYSQL_TYPE_STRING, 0, 0, 0,

   SKIP_OPEN_TABLE},

  {"SQL_PATH", FN_REFLEN, MYSQL_TYPE_STRING, 0, 1, 0, SKIP_OPEN_TABLE},

  {"SCHEMA_COMMENT", DATABASE_COMMENT_MAXLEN, MYSQL_TYPE_STRING, 0, 0, 0,

   SKIP_OPEN_TABLE},

  {0, 0, MYSQL_TYPE_STRING, 0, 0, 0, SKIP_OPEN_TABLE}

};

It has two problems:

• It's not friently for user plugins, which may want to create INFORMATION_SCHEMA tables with their own data types.
• When a Field is created inside Type_handler_xxx::make_schema_field(), strlen() is called for ST_FIELD_INFO::field_name, for every column, every time an INFORMATION_SCHEMA query is done. This is not performance wise.

To solve these problems let do the following:

• Add a namespace Show
• Add a helper class Show::Column
• Add a number of Show classes for various data types, with this hierarchy:

  Type

  Blob

  Varchar

  Yesno

  Catalog

  Name

  Definer

  Userhost

  CSName

  SQLMode

  Longtext

  Datetime

  Decimal

  ULonglong

  ULong

  SLonglong

  SLong

  SShort

  STiny

  Double

This will hide internal implementation details of ST_FIELD_INFO from the upper level code. An INFORMATION_SCHEMA table definition will look like this:

namespace Show {

ST_FIELD_INFO schema_fields_info[]=

{

  Column("CATALOG_NAME",               Catalog(),        NOT_NULL),

  Column("SCHEMA_NAME",                Name(),           NOT_NULL, "Database"),

  Column("DEFAULT_CHARACTER_SET_NAME", CSName(),         NOT_NULL),

  Column("DEFAULT_COLLATION_NAME",     CSName(),         NOT_NULL),

  Column("SQL_PATH",                   Str(FN_REFLEN),   NULLABLE),

  Column("SCHEMA_COMMENT", Str(DATABASE_COMMENT_MAXLEN), NOT_NULL),

  CEnd()

};

...

} // namespace Show

This task covers the code in /sql and /plugins.

As the next step, in separate patchs, we'll do the following:

• Fix the code in /storage to use the new classes instead of direct ST_FIELD_INFO initialization.
• In ST_FIELD_INFO, replace enum_field_types field_type to const Type_handler *handler.
• In ST_FIELD_INFO, replace const char *field_name to LEX_CSTRING field_name.
  which will solve the two mentioned problems.