Rows that store variable-length data require more overhead than rows that contain only fixed-length data, so there are two separate formulas for computing the size of a data row.
Use this formula if the table contains only fixed-length columns, and all are defined as NOT NULL.
Formula |
||
|---|---|---|
4 |
(Overhead) |
|
+ |
Sum of bytes in all fixed-length columns |
|
= Data row size |
||
Use this formula if the table contains any variable-length columns or columns that allow null values.
The table in the example contains variable-length columns, so the computations are shown in the right column.
Formula |
Example |
||||
|---|---|---|---|---|---|
4 |
(Overhead) |
4 |
|||
+ |
Sum of bytes in all fixed-length columns |
+ |
100 |
||
+ |
Sum of bytes in all variable-length columns |
+ |
50 |
||
= Subtotal |
154 |
||||
|
|
||||
+ |
|
(Subtotal / 256) + 1 (Overhead) |
1 |
||
+ |
|
Number of variable-length columns + 1 |
3 |
||
+ |
2 |
(Overhead) |
2 |
||
= Data row size |
160 |
||||
