Нет, новые записи не будут занимать меньше места. Я смотрел на этот точный вопрос ранее сегодня, как это происходит.
Тестовый стол
CREATE TABLE T
(
id int identity primary key,
FixedWidthColToBeDropped char(10),
VariableWidthColToBeDropped varchar(10),
FixedWidthColToBeWidened char(7),
FixedWidthColToBeShortened char(20),
VariableWidthColToBeWidened varchar(7),
VariableWidthColToBeShortened varchar(20),
VariableWidthColWontBeAltered varchar(20)
)
Запрос смещений
WITH T
AS (SELECT ISNULL(LEFT(MAX(name), 30), 'Dropped') AS column_name,
MAX(column_id) AS column_id,
ISNULL(MAX(case
when column_id IS NOT NULL THEN max_inrow_length
END), MAX(max_inrow_length)) AS max_inrow_length,
leaf_offset,
CASE
WHEN leaf_offset < 0 THEN SUM(CASE
WHEN column_id IS NULL THEN 2 ELSE 0
END)
ELSE MAX(max_inrow_length) - MAX(CASE
WHEN column_id IS NULL THEN 0
ELSE max_inrow_length
END)
END AS wasted_space
FROM sys.system_internals_partition_columns pc
JOIN sys.partitions p
ON p.partition_id = pc.partition_id
LEFT JOIN sys.columns c
ON column_id = partition_column_id
AND c.object_id = p.object_id
WHERE p.object_id = object_id('T')
GROUP BY leaf_offset)
SELECT CASE
WHEN GROUPING(column_name) = 0 THEN column_name
ELSE 'Total'
END AS column_name,
column_id,
max_inrow_length,
leaf_offset,
SUM(wasted_space) AS wasted_space
FROM T
GROUP BY ROLLUP ((column_name,
column_id,
max_inrow_length,
leaf_offset))
ORDER BY GROUPING(column_name),
CASE
WHEN leaf_offset > 0 THEN leaf_offset
ELSE 10000 - leaf_offset
END
Исходное состояние таблицы
column_name column_id max_inrow_length leaf_offset wasted_space
------------------------------ ----------- ---------------- ----------- ------------
id 1 4 4 0
FixedWidthColToBeDropped 2 10 8 0
FixedWidthColToBeWidened 4 7 18 0
FixedWidthColToBeShortened 5 20 25 0
VariableWidthColToBeDropped 3 10 -1 0
VariableWidthColToBeWidened 6 7 -2 0
VariableWidthColToBeShortened 7 20 -3 0
VariableWidthColWontBeAltered 8 20 -4 0
Total NULL NULL NULL 0
Теперь внесите некоторые изменения
ALTER TABLE T
ALTER COLUMN FixedWidthColToBeWidened char(12)
ALTER TABLE T
ALTER COLUMN FixedWidthColToBeShortened char(10)
ALTER TABLE T
ALTER COLUMN VariableWidthColToBeWidened varchar(12)
ALTER TABLE T
ALTER COLUMN VariableWidthColToBeShortened varchar(10)
ALTER TABLE T
DROP COLUMN FixedWidthColToBeDropped, VariableWidthColToBeDropped
Посмотрите на стол снова
column_name column_id max_inrow_length leaf_offset wasted_space
------------------------------ ----------- ---------------- ----------- ------------
id 1 4 4 0
Dropped NULL 10 8 10
Dropped NULL 7 18 7
FixedWidthColToBeShortened 5 10 25 10
FixedWidthColToBeWidened 4 12 45 0
Dropped NULL 10 -1 2
VariableWidthColToBeWidened 6 12 -2 0
Dropped NULL 20 -3 2
VariableWidthColWontBeAltered 8 20 -4 0
VariableWidthColToBeShortened 7 10 -5 0
Total NULL NULL NULL 31
Вставьте строку и посмотрите на страницу
INSERT INTO T
([FixedWidthColToBeWidened]
,[FixedWidthColToBeShortened]
,[VariableWidthColToBeWidened]
,[VariableWidthColToBeShortened])
VALUES
('1','2','3','4')
DECLARE @DBCCPAGE nvarchar(100)
SELECT TOP 1 @DBCCPAGE = 'DBCC PAGE(''tempdb'',' + CAST(file_id AS VARCHAR) + ',' + CAST(page_id AS VARCHAR) + ',3)'
FROM T
CROSS APPLY sys.fn_PhysLocCracker(%%physloc%%)
DBCC TRACEON(3604)
EXEC (@DBCCPAGE)
Возвращает
Record Type = PRIMARY_RECORD Record Attributes = NULL_BITMAP VARIABLE_COLUMNS
Record Size = 75
Memory Dump @0x000000000D5CA060
0000000000000000: 30003900 01000000 26a44500 00000000 †0.9.....&¤E.....
0000000000000010: ffffffff ffffff7f 00322020 20202020 †ÿÿÿÿÿÿÿ..2
0000000000000020: 20202003 00000000 98935c0d 00312020 † ......\..1
0000000000000030: 20202020 20202020 200a0080 00050049 † ......I
0000000000000040: 004a004a 004a004b 003334†††††††††††††.J.J.J.K.34
Slot 0 Column 1 Offset 0x4 Length 4 Length (physical) 4
id = 1
Slot 0 Column 67108868 Offset 0x8 Length 0 Length (physical) 10
DROPPED = NULL
Slot 0 Column 67108869 Offset 0x0 Length 0 Length (physical) 0
DROPPED = NULL
Slot 0 Column 67108865 Offset 0x12 Length 0 Length (physical) 7
DROPPED = NULL
Slot 0 Column 67108866 Offset 0x19 Length 0 Length (physical) 20
DROPPED = NULL
Slot 0 Column 6 Offset 0x49 Length 1 Length (physical) 1
VariableWidthColToBeWidened = 3
Slot 0 Column 67108867 Offset 0x0 Length 0 Length (physical) 0
DROPPED = NULL
Slot 0 Column 8 Offset 0x0 Length 0 Length (physical) 0
VariableWidthColWontBeAltered = [NULL]
Slot 0 Column 4 Offset 0x2d Length 12 Length (physical) 12
FixedWidthColToBeWidened = 1
Slot 0 Column 5 Offset 0x19 Length 10 Length (physical) 10
FixedWidthColToBeShortened = 2
Slot 0 Column 7 Offset 0x4a Length 1 Length (physical) 1
VariableWidthColToBeShortened = 4
Slot 0 Offset 0x0 Length 0 Length (physical) 0
KeyHashValue = (010086470766)
Вы можете видеть, что удаленные (и измененные) столбцы по-прежнему занимают место, хотя таблица была фактически пустой при изменении схемы.
Влияние пропущенных столбцов в вашем случае будет потрачено 15 байт для char один и 2 байта для varchar один , если это последний столбец в разделе переменных когда это не займет места.