Is it a good idea to use COLUMN AS (left([Another_Column],(4)) instead of LEFT in the select?Which problems...
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Is it a good idea to use COLUMN AS (left([Another_Column],(4)) instead of LEFT in the select?
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I came across a table like this:
CREATE TABLE TABLE1
(
CD1 int
,CD2 varchar(16)
,CD3 varchar(21)
,CD4 decimal(14,0)
,CD5 varchar(4)
,CD6 decimal(18,2)
,CD7 AS (left([CD3],(4)))
)
This table has more than 4 BILLION rows (totally unnecessary, but this is another topic).
As you can see in the last column, they use AS (left([CD3],(4))). I think this is pretty useless, since we almost NEVER have a SELECT on this table, and here is just using space.
Isn't it better to select that field during the select when needed?
sql-server sql-server-2008-r2 t-sql
edited Mar 28 at 19:41
Josh Darnell
7,43522241
asked Mar 28 at 12:48
Racer SQLRacer SQL
3,10342564
add a comment |
I came across a table like this:
CREATE TABLE TABLE1
(
CD1 int
,CD2 varchar(16)
,CD3 varchar(21)
,CD4 decimal(14,0)
,CD5 varchar(4)
,CD6 decimal(18,2)
,CD7 AS (left([CD3],(4)))
)
This table has more than 4 BILLION rows (totally unnecessary, but this is another topic).
As you can see in the last column, they use AS (left([CD3],(4))). I think this is pretty useless, since we almost NEVER have a SELECT on this table, and here is just using space.
Isn't it better to select that field during the select when needed?
sql-server sql-server-2008-r2 t-sql
edited Mar 28 at 19:41
Josh Darnell
7,43522241
asked Mar 28 at 12:48
Racer SQLRacer SQL
3,10342564
1
There is a thin chance of getting some more usable statistics. Other than that, probably nothing. But it doesn't use space either :)
– dean
Mar 28 at 18:12
add a comment |
I came across a table like this:
CREATE TABLE TABLE1
(
CD1 int
,CD2 varchar(16)
,CD3 varchar(21)
,CD4 decimal(14,0)
,CD5 varchar(4)
,CD6 decimal(18,2)
,CD7 AS (left([CD3],(4)))
)
This table has more than 4 BILLION rows (totally unnecessary, but this is another topic).
As you can see in the last column, they use AS (left([CD3],(4))). I think this is pretty useless, since we almost NEVER have a SELECT on this table, and here is just using space.
Isn't it better to select that field during the select when needed?
sql-server sql-server-2008-r2 t-sql
edited Mar 28 at 19:41
Josh Darnell
7,43522241
asked Mar 28 at 12:48
Racer SQLRacer SQL
3,10342564
I came across a table like this:
CREATE TABLE TABLE1
(
CD1 int
,CD2 varchar(16)
,CD3 varchar(21)
,CD4 decimal(14,0)
,CD5 varchar(4)
,CD6 decimal(18,2)
,CD7 AS (left([CD3],(4)))
)
This table has more than 4 BILLION rows (totally unnecessary, but this is another topic).
As you can see in the last column, they use AS (left([CD3],(4))). I think this is pretty useless, since we almost NEVER have a SELECT on this table, and here is just using space.
Isn't it better to select that field during the select when needed?
sql-server sql-server-2008-r2 t-sql
sql-server sql-server-2008-r2 t-sql
edited Mar 28 at 19:41
Josh Darnell
7,43522241
asked Mar 28 at 12:48
Racer SQLRacer SQL
3,10342564
edited Mar 28 at 19:41
Josh Darnell
7,43522241
asked Mar 28 at 12:48
Racer SQLRacer SQL
3,10342564
edited Mar 28 at 19:41
Josh Darnell
7,43522241
edited Mar 28 at 19:41
Josh Darnell
7,43522241
edited Mar 28 at 19:41
Josh Darnell
7,43522241
7,43522241
asked Mar 28 at 12:48
Racer SQLRacer SQL
3,10342564
asked Mar 28 at 12:48
Racer SQLRacer SQL
3,10342564
asked Mar 28 at 12:48
Racer SQLRacer SQL
3,10342564
3,10342564
1
There is a thin chance of getting some more usable statistics. Other than that, probably nothing. But it doesn't use space either :)
– dean
Mar 28 at 18:12
add a comment |
1
There is a thin chance of getting some more usable statistics. Other than that, probably nothing. But it doesn't use space either :)
– dean
Mar 28 at 18:12
1
1
There is a thin chance of getting some more usable statistics. Other than that, probably nothing. But it doesn't use space either :)
– dean
Mar 28 at 18:12
There is a thin chance of getting some more usable statistics. Other than that, probably nothing. But it doesn't use space either :)
– dean
Mar 28 at 18:12
add a comment |
2 Answers
2
active
oldest
votes
If the computed column isn't persisted or indexed, it's only a virtual column (expression), and it's not taking up any "space".
answered Mar 28 at 12:49
Erik DarlingErik Darling
22.6k1269112
add a comment |
The only reason I can think of for having that column is to index it, because there is some common set of read queries that filter on the first few characters in CD3.
If the computed column is, indeed, indexed, then the it's valuable because:
- it would required less storage than the full 21 char column
- it would incur less page reads for seeks and scans than an index on the full 21 char column
You mentioned the table is rarely read, but I would check for indexes that use this computed column to be sure.
If it's not indexed, then see Erik's answer about the storage aspect of non-persisted computed columns.
answered Mar 28 at 19:40
Josh DarnellJosh Darnell
7,43522241
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
If the computed column isn't persisted or indexed, it's only a virtual column (expression), and it's not taking up any "space".
answered Mar 28 at 12:49
Erik DarlingErik Darling
22.6k1269112
add a comment |
If the computed column isn't persisted or indexed, it's only a virtual column (expression), and it's not taking up any "space".
answered Mar 28 at 12:49
Erik DarlingErik Darling
22.6k1269112
add a comment |
If the computed column isn't persisted or indexed, it's only a virtual column (expression), and it's not taking up any "space".
answered Mar 28 at 12:49
Erik DarlingErik Darling
22.6k1269112
If the computed column isn't persisted or indexed, it's only a virtual column (expression), and it's not taking up any "space".
answered Mar 28 at 12:49
Erik DarlingErik Darling
22.6k1269112
answered Mar 28 at 12:49
Erik DarlingErik Darling
22.6k1269112
answered Mar 28 at 12:49
Erik DarlingErik Darling
22.6k1269112
answered Mar 28 at 12:49
Erik DarlingErik Darling
22.6k1269112
22.6k1269112
add a comment |
add a comment |
The only reason I can think of for having that column is to index it, because there is some common set of read queries that filter on the first few characters in CD3.
If the computed column is, indeed, indexed, then the it's valuable because:
- it would required less storage than the full 21 char column
- it would incur less page reads for seeks and scans than an index on the full 21 char column
You mentioned the table is rarely read, but I would check for indexes that use this computed column to be sure.
If it's not indexed, then see Erik's answer about the storage aspect of non-persisted computed columns.
answered Mar 28 at 19:40
Josh DarnellJosh Darnell
7,43522241
add a comment |
The only reason I can think of for having that column is to index it, because there is some common set of read queries that filter on the first few characters in CD3.
If the computed column is, indeed, indexed, then the it's valuable because:
- it would required less storage than the full 21 char column
- it would incur less page reads for seeks and scans than an index on the full 21 char column
You mentioned the table is rarely read, but I would check for indexes that use this computed column to be sure.
If it's not indexed, then see Erik's answer about the storage aspect of non-persisted computed columns.
answered Mar 28 at 19:40
Josh DarnellJosh Darnell
7,43522241
add a comment |
The only reason I can think of for having that column is to index it, because there is some common set of read queries that filter on the first few characters in CD3.
If the computed column is, indeed, indexed, then the it's valuable because:
- it would required less storage than the full 21 char column
- it would incur less page reads for seeks and scans than an index on the full 21 char column
You mentioned the table is rarely read, but I would check for indexes that use this computed column to be sure.
If it's not indexed, then see Erik's answer about the storage aspect of non-persisted computed columns.
answered Mar 28 at 19:40
Josh DarnellJosh Darnell
7,43522241
The only reason I can think of for having that column is to index it, because there is some common set of read queries that filter on the first few characters in CD3.
If the computed column is, indeed, indexed, then the it's valuable because:
- it would required less storage than the full 21 char column
- it would incur less page reads for seeks and scans than an index on the full 21 char column
You mentioned the table is rarely read, but I would check for indexes that use this computed column to be sure.
If it's not indexed, then see Erik's answer about the storage aspect of non-persisted computed columns.
answered Mar 28 at 19:40
Josh DarnellJosh Darnell
7,43522241
answered Mar 28 at 19:40
Josh DarnellJosh Darnell
7,43522241
answered Mar 28 at 19:40
Josh DarnellJosh Darnell
7,43522241
answered Mar 28 at 19:40
Josh DarnellJosh Darnell
7,43522241
7,43522241
add a comment |
add a comment |
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There is a thin chance of getting some more usable statistics. Other than that, probably nothing. But it doesn't use space either :)
– dean
Mar 28 at 18:12