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Values in VARCHAR columns are variable-length strings. The length can be specified as a value from 0 to 65,535. The effective maximum length of a VARCHAR is subject to the maximum row size (65,535 bytes, which is shared among all columns) and the character set used.
In contrast to CHAR, VARCHAR values are stored as a one-byte or two-byte length prefix plus data. The length prefix indicates the number of bytes in the value. A column uses one length byte if values require no more than 255 bytes, two length bytes if values may require more than 255 bytes.
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The following table illustrates the differences between CHAR and VARCHAR by showing the result of storing various string values into CHAR(4) and VARCHAR(4) columns (assuming that the column uses a single-byte character set such as latin1).
Value
CHAR(4)
Storage Required
VARCHAR(4)
Storage Required
''
' '
4 bytes
''
1 byte
'ab'
'ab '
4 bytes
'ab'
3 bytes
'abcd'
'abcd'
4 bytes
'abcd'
5 bytes
'abcdefgh'
'abcd'
4 bytes
'abcd'
5 bytes
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7.2.14 Speed of INSERT Statements
The time to insert a record is determined by the following factors, where the numbers indicate approximate proportions:
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BatchFile code
+------+--------+-------+
| f_PY | cBegin | cEnd |
+------+--------+-------+
| A | 45217 | 45252 |
| B | 45253 | 45760 |
.....
| Z | 54481 | 55289 |
+------+--------+------- ......