JET_COLUMNCREATE Structure

Windows

The JET_COLUMNCREATE structure describes a column to create in a database.

typedef struct tag_JET_COLUMNCREATE {
  unsigned long cbStruct;
  tchar* szColumnName;
  JET_COLTYP coltyp;
  unsigned long cbMax;
  JET_GRBIT grbit;
  void* pvDefault;
  unsigned long cbDefault;
  unsigned long cp;
  JET_COLUMNID columnid;
  JET_ERR err;
} JET_COLUMNCREATE;

Members

cbStruct

The size of the structure, in bytes. This field must be initialized to sizeof( JET_COLUMNCREATE ).

szColumnName

The name of the column to create. The name must meet the following criteria:

  • It must be fewer than JET_cbNameMost characters in length, not including the terminating NULL.

  • It must contain characters only from the following sets: 0 through 9, A through Z, a through z, and all other punctuation except for exclamation point (!), comma (,), opening bracket ([), and closing bracket (]), that is, ASCII characters 0x20, 0x22 through 0x2d, 0x2f through 0x5a, 0x5c, 0x5d through 0x7f.

  • It cannot begin with a space.

  • It must contain at least one non-space character.

coltyp

The type of the column (for example, text, binary, or numerical). For more information, see JET_COLTYP.

cbMax

The maximum length, in bytes, of a variable-length column. The length of the column for fixed-length columns.

grbit

A group of bits that contain the options for this structure, and which include zero or more of the following values.

Value

Meaning

JET_bitColumnFixed

The column is fixed. It will always use the same amount of space in a row, regardless of how much data is being stored in the column. JET_bitColumnFixed cannot be used with JET_bitColumnTagged. This bit cannot be used with long values such as JET_coltypLongText and JET_coltypLongBinary.

JET_bitColumnTagged

The column is tagged. Tagged columns do not take up any space in the database if they do not contain data. This bit cannot be used with JET_bitColumnFixed.

JET_bitColumnNotNULL

The column must never be set to a NULL value.

JET_bitColumnAutoincrement

The column is automatically incremented. The number is an increasing number, and is guaranteed to be unique within a table. The number, however, might not be continuous. For example, if five rows are inserted into a table, the autoincrement column could contain the values { 1, 2, 6, 7, 8 }.

Windows 2000:  This bit can be used only on columns of type JET_coltypLong.

Windows Server 2003 and later:  This bit can only be used on columns of type JET_coltypLong or JET_coltypCurrency.

JET_bitColumnUpdatable

This bit is valid only on calls to JetGetColumnInfo.

JET_bitColumnTTKey

This bit is valid only on calls to JetOpenTempTable.

JET_bitColumnTTDescending

This bit is valid only on calls to JetOpenTempTable.

JET_bitColumnMultiValued

The column can be multi-valued. A multi-valued column can have zero, one, or more values associated with it. The various values in a multi-valued column are identified by the itagSequence member of various structures, for example, JET_RETINFO, JET_SETINFO, JET_SETCOLUMN, JET_RETRIEVECOLUMN, JET_ENUMCOLUMNVALUE. Multi-valued columns must be tagged columns; that is, they cannot be fixed-length or variable-length columns.

JET_bitColumnEscrowUpdate

The column is an escrow update column. An escrow update column can be updated concurrently by different sessions with JetEscrowUpdate and maintain transactional consistency.

  • An escrow update column can be created only when the table is empty.

  • An escrow update column must be of type JET_coltypLong.

  • An escrow update column must have a default value (that is cbDefault must be positive).

  • JET_bitColumnEscrowUpdate cannot be used in conjunction with the following constants:

    • JET_bitColumnTagged

    • JET_bitColumnVersion

    • JET_bitColumnAutoincrement

JET_bitColumnUnversioned

The column is created without a version. Other transactions attempting to add a column with the same name will fail. This bit is only useful with JetAddColumn. It cannot be used within a transaction.

JET_bitColumnMaybeNull

Reserved for future use.

JET_bitColumnFinalize

Use JET_bitColumnDeleteOnZero instead of JET_bitColumnFinalize. JET_bitColumnFinalize specifies that a column can be finalized. When a column that can be finalized has an escrow update column that reaches zero, the row will be deleted. Future versions can invoke a callback function instead. For more information, see JET_CALLBACK. A column that can be finalized must be an escrow update column. JET_bitColumnFinalize cannot be used with JET_bitColumnUserDefinedDefault.

JET_bitColumnUserDefinedDefault

The default value for a column is provided by the callback function, JET_CALLBACK. A column that has a user-defined default must be a tagged column. pvDefault must point to a JET_USERDEFINEDDEFAULT structure, and cbDefault must be set to sizeof(JET_USERDEFINEDDEFAULT).

JET_bitColumnUserDefinedDefault cannot be used in conjunction with the following constants:

  • JET_bitColumnFixed

  • JET_bitColumnNotNULL

  • JET_bitColumnVersion

  • JET_bitColumnAutoincrement

  • JET_bitColumnUpdatable

  • JET_bitColumnEscrowUpdate

  • JET_bitColumnFinalize

  • JET_bitColumnDeleteOnZero

  • JET_bitColumnMaybeNull

JET_bitColumnDeleteOnZero

The column is an escrow update column, and when it reaches zero, the record will be deleted. A common use for a column that can be finalized is to use it as a reference count field, and when the field reaches zero the record gets deleted. JET_bitColumnDeleteOnZero is related to JET_bitColumnFinalize. A delete-on-zero column must be an escrow update column. JET_bitColumnDeleteOnZero cannot be used with JET_bitColumnFinalize. JET_bitColumnDeleteOnZero cannot be used with user defined default columns.

pvDefault

Points to a buffer which will be the default value for a column. The length of the buffer is cbDefault. If there is no default, pvDefault should be set to NULL and cbDefault should be set to zero. If grbit has JET_bitColumnUserDefinedDefault set, pvDefault will be interpreted as a pointer to a JET_USERDEFINEDDEFAULT structure. Default values cannot be larger than 255 bytes. If a default value is larger than 255 bytes, it will be silently truncated.

cbDefault

The size, in bytes, of the buffer specified by pvDefault.

cp

The code page for the column. The only valid values for text columns are English (1252) and Unicode (1200). A value of zero means the default will be used (English, 1252). If the column is not a text column, the code page automatically gets set to zero.

columnid

On success, the column identifier of the newly-created column will be passed back in this field. On failure, the value is undefined.

err

The err field will contain the status of creating this column. See JetAddColumn for a list of likely return values.

Requirements

Client

Requires Windows Vista, Windows XP, or Windows 2000 Professional.

Server

Requires Windows Server 2008, Windows Server 2003, or Windows 2000 Server.

Header

Declared in Esent.h.

Unicode

Implemented as JET_COLUMNCREATE_W (Unicode) and JET_COLUMNCREATE_A (ANSI).

See Also

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