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Column name
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Data type
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Length
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LOB unit
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Precision
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Scale
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LOB option
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Bit data
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Default
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Nullable
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Comment
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OK
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Cancel
Column name
This field displays the name currently specified for the column that
you're altering. You cannot alter this field for an existing
column. To specify a different name for a column that you're
adding, type the new name for the column in this field. This
name:
Attention: You cannot use the same name for more than one
column of the table.
Data type
This box contains the data type currently specified for the column.
You cannot alter this box for an existing column. To specify a
different data type for a column that you're adding, click on the down
arrow to display a list of data types and select one.
The data type can be one of:
- INTEGER
- For a large integer with a precision of 11 digits.
- SMALLINT
- For a small integer with a precision of 5 digits.
- BIGINT
- For a large integer with a precision of 19 digits.
- DOUBLE
- For a floating-point number. Double Precision and Float are
synonyms for Double.
- DECIMAL
- For a decimal number.
- CHARACTER
- For a fixed-length character string.
- VARCHAR
- For a varying-length character string with a maximum length of
4000.
- LONG VARCHAR
- For a varying-length character string with a maximum length of
32700.
- BLOB
- For a binary large object string.
- CLOB
- For a character large object string.
- DBCLOB
- For a double-byte character large object string.
- GRAPHIC
- For a fixed-length graphic string.
- VARGRAPHIC
- For a varying-length graphic string with a maximum length of 2000.
- LONG VARGRAPHIC
- For a varying-length graphic string with a maximum length of 16350.
- DATE
- For a date.
- TIME
- For a time.
- TIMESTAMP
- For a timestamp.
- Distinct type
- For a distinct type. Distinct types are listed in the form of
schema.type.
- REAL
- For a single-precision floating-point number.
Length
This field displays the length (byte count) currently specified for the
column. To specify a different length for a column that you are adding,
(or an existing VARCHAR column that you are changing), type a new value in
this field based on the specified data type:
- CHARACTER
- Length of the fixed-length character string, which can range from 1 to
254.
- VARCHAR
- Maximum length of the varying-length character string, which can range
from 1 to 4000.
- BLOB
- Maximum length of the BLOB string, which can range from 1 to
2147483647. If a LOB unit of Kbytes, Mbytes, or Gbytes is specified in
the LOB unit box, the maximum value of Length is limited
as follows:
- Kbytes
- The maximum value for this field is 2097152. Each KB is equivalent
to 1024 bytes, so the maximum length in bytes is 1024 times the integer value
you specify in this field.
- Mbytes
- The maximum value for this field is 2048. Each MB is equivalent to
1048576 bytes, so the maximum length in bytes is 1048576 times the integer
value you specify in this field.
- Gbytes
- The maximum value for this field is 2. Each GB is equivalent to
1073741824 bytes, so the maximum length in bytes is 1073741824 times the
integer value you specify in this field.
- CLOB
- Maximum length of the CLOB string, which can range from 1 to
2147483647. If a LOB unit of Kbytes, Mbytes, or Gbytes is specified in
the LOB unit box, the maximum value of Length is limited
as follows:
- Kbytes
- The maximum value for this field is 2097152. Each KB is equivalent
to 1024 bytes, so the maximum length in bytes is 1024 times the integer value
you specify in this field.
- Mbytes
- The maximum value for this field is 2048. Each MB is equivalent to
1048576 bytes, so the maximum length in bytes is 1048576 times the integer
value you specify in this field.
- Gbytes
- The maximum value for this field is 2. Each GB is equivalent to
1073741824 bytes, so the maximum length in bytes is 1073741824 times the
integer value you specify in this field.
- DBCLOB
- Maximum length of the DBCLOB string, which can range from 1 to 1073741823
double-byte characters. If a LOB unit of Kbytes, Mbytes, or Gbytes is
specified in the LOB unit box, the maximum value of
Length is limited as follows:
- Kbytes
- The maximum value for this field is 1048576. Each KB is equivalent
to 1024 bytes, so the maximum length in double bytes is 1024 times the integer
value you specify in this field.
- Mbytes
- The maximum value for this field is 1024. Each MB is equivalent to
1048576 bytes, so the maximum length in double bytes is 1048576 times the
integer value you specify in this field.
- Gbytes
- The maximum value for this field is 1. Each GB is equivalent to
1073741824 bytes, so the maximum length in double bytes is 1073741824 times
the integer value you specify in this field.
- GRAPHIC
- Length of the fixed-length graphic string, which can range from 1 to
127. If the length is not specified, a length of 1 is assumed.
- VARGRAPHIC
- Maximum length of the varying-length graphic string, which can range from
1 to 2000.
This field is available only if you specified CHARACTER, VARCHAR, BLOB,
CLOB, DBCLOB, GRAPHIC, or VARGRAPHIC in the Data type box and only
for a new column.
LOB unit
This box contains the LOB unit currently specified for the column.
You cannot alter this box for an existing column. To specify a
different multiplier for the length of a column that you're adding of
data type BLOB, CLOB, or DBCLOB, select one of the following LOB units:
- Bytes
- The maximum length is the value specified in the Length
box. The maximum value of Length is 2147483647 for BLOB or
CLOB data. For DBCLOB data, the maximum value is 1073741823 because a
DBCLOB string is in double-byte characters.
- Kbytes
- The maximum length is 1024 times the value specified in the
Length box. The maximum value of Length is
2097152 for BLOB or CLOB data. For DBCLOB data, the maximum value is
1048576 because a DBCLOB string is in double-byte characters.
- Mbytes
- The maximum length is 1048576 times the value specified in the
Length box. The maximum value of Length is 2048
for BLOB or CLOB data. For DBCLOB data, the maximum value is 1024
because a DBCLOB string is in double-byte characters.
- Gbytes
- The maximum length is 1073741824 times the value specified in the
Length box. The maximum value of Length is 2 for
BLOB or CLOB data. For DBCLOB data, the maximum value is 1 because a
DBCLOB string is in double-byte characters.
This box is available only if you specified BLOB, CLOB, or DBCLOB in the
Data type box and only for a new column.
Precision
This field displays the precision currently specified for the column of
data type DECIMAL. You cannot alter this field for an existing
column. To change the precision for a column that you're adding,
type a new value in this field. The precision is the total number of
digits in a DECIMAL number, which can range from 1 to 31. If you do not
specify the precision, a default value of 5 is used.
This field is available only if you specified DECIMAL in theData
type box and only for a new column.
Scale
This field displays the scale currently specified for the column of data
type DECIMAL. You cannot alter this field for an existing
column. To change the scale for a column that you're adding, type
a new value in this field. The scale is the number of digits to the
right of the decimal point, which can range from 0 to the precision of the
number. If you do not specify the scale, a default value of 0 is
used.
This field is available only if you specified DECIMAL in theData
type box and only for a new column.
LOB option
These check boxes display the LOB options currently selected for the column
of LOB data types. You cannot alter these check boxes for an existing
column. To change the LOB options for a column that you're adding,
select or clear the following check boxes:
- Logged
- Specifies that changes made to the column be written to the log.
The data in such columns is then recoverable with database utilities, such as
RESTORE DATABASE. The implication of not logging is that during a
roll-forward operation, after a backup or load operation, the LOB values that
would have had log records replayed during the roll-forward are replaced by
zeroes. During crash recovery, all committed changes and changes rolled
back will reflect the expected results.
| Note: | LOBs greater than 1 GB cannot be logged, and LOBs greater than 10 MB should
not be logged.
|
- Compact
- Specifies that the values in the LOB column should take up minimal disk
space (free any extra disk pages in the last group used by the LOB value),
rather than leave any left-over space at the end of the LOB storage area that
might facilitate subsequent append operations.
| Note: | Storing data in this way can cause a performance penalty in any append
(length-increasing) operations on the column.
|
These check boxes are available only if you specified a data type of BLOB,
CLOB, DBCLOB, or a distinct type with any of these as source types in the
Data type box and only for a new column.
Bit data
This check box is displayed as currently specified for the column.
You cannot alter this check box for an existing column. For a column
that you're adding, you can select or clear this check box to change the
setting. If you select this check box, the contents of the column will
be treated as bit (binary) data. During data exchange with other
systems, code page conversions are not performed. Comparisons are done
in binary, irrespective of the database collating sequence.
This check box is available only if you specified a data type of CHARACTER,
VARCHAR, or LONG VARCHAR in the Data type box and only for a new
column.
Default
This field displays the default value currently specified for the
column. You cannot alter this field for an existing column. To
change the default value for a column that you're adding, type the
constant value, CURRENT DATE, CURRENT TIME, CURRENT TIMESTAMP, USER, or NULL
in this field. The default value you type will be used exactly as
entered. For example, if you put double quotes around the value you
type in, the double quotes will be part of the default value. If you do
not specify a specific default value, the default value depends on the data
type of the column as shown in the following table.
Table 2. Default Values (when no value specified)
| Data Type
| Default Value
|
| Numeric
| 0
|
| Fixed-length character string
| Blanks
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| Varying-length character string
| A string of length 0
|
| Fixed-length graphic string
| Double-byte blanks
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| Varying-length graphic string
| A string of length 0
|
| Date
| For existing rows, a date corresponding to January 1, 0001. For
added rows, the current date.
|
| Time
| For existing rows, a time corresponding to 0 hours, 0 minutes, and 0
seconds. For added rows, the current time.
|
| Timestamp
| For existing rows, a date corresponding to January 1, 0001, and a time
corresponding to 0 hours, 0 minutes, 0 seconds and 0 microseconds. For
added rows, the current timestamp.
|
| Binary string (BLOB)
| A string of length 0
|
You can specify the following types of default values:
- Constant
- Specifies the constant you specify as the default value for the
column. The specified constant must:
- Represent a value that can be assigned to the column in accordance with
the rules of assignment
- Not be a floating-point constant unless the column is defined with a
floating-point data type
- Not have nonzero digits beyond the scale of the column data type if the
constant is a DECIMAL constant
- Be expressed with no more than 254 characters including the quote
characters, any introducer character such as the X for a hexadecimal constant,
characters from the fully qualified function name, and parentheses when the
constant is the argument of a cast-function
- Be expressed in the following way:
- 'character string' for a character constant
- X'hexadecimal string' for a hexadecimal constant
- G'double-byte character string' or
N'double-byte character string' for a graphic constant
- Datetime special register
- Specifies the value of the datetime special register (CURRENT DATE,
CURRENT TIME, or CURRENT TIMESTAMP) at the time of INSERT or UPDATE as the
default for the column. The data type of the column must be the data
type that corresponds to the special register specified.
- USER
- Specifies the value of the USER special register at the time of INSERT or
UPDATE as the default for the column. If USER is specified, the data
type of the column must be a character string with a length not less than the
length attribute of USER.
- NULL
- Specifies NULL as the default for the column. If the
Nullable check box is not selected, NULL can be specified as the
default but any attempt to set the column to the default value will result in
an error.
- Cast function
- This form of a default value can be used only with columns defined as a
distinct type, BLOB, or DATETIME data type.
Nullable
This check box is displayed as currently specified for the column.
You cannot alter this check box for an existing column. For a column
that you're adding, you can select or clear this check box to change the
setting. If you select this check box, the column can contain null
values. The default value for the column is either the null value or
the value specified in the Default field.
Attention: If the column will be a primary key column, it
cannot be nullable.
Comment
Optional: This field contains the comment currently specified for the
column. To change the comment, type the new comment in this
field. You can type up to 254 characters, including embedded
blanks.