1. Proper DataType Usage = Guaranteed Better Performance and Accuracy
Vern Rabe RabeData, LLC
Proper DataType Usage = Guaranteed Better Performance and Accuracy

2. Vern Rabe
Portland, OR independent consultant, trainer MCTA, MCDBA, MCSE, MCITP Co-VP Oregon PASS chapter Working with/focusing on SQL Server since 1993, starting with SQL Server 4.21a My first PC had a 10MB hard drive

3. What We’ll Cover Why do we care? Data Type by Data type
Performance, accuracy
Data Type by Data type
When to use which
Functions and Nuggets
What to use, what not to use, some workarounds

4. Why Important? Accuracy • Performance •
SARGable (Implicit Conversion) •

5. Implicit Conversion Data Type Precedence
user-defined data types (highest)
sql_variant
xml
datetimeoffset
datetime2
datetime
smalldatetime
date
time
float
real
decimal
money
smallmoney
bigint
int
smallint
tinyint
bit
ntext
text
image
rownumber
uniqueidentifier
nvarchar
nchar
varchar
char
varbinary
binary (lowest)

6. Data Type Categories
Numeric Character Temporal Binary Other

7. Numeric Category
bit : 0 or 1 tinyint : 1 byte : 0 to 255 smallint : 2 bytes : -32,768 to 32,767 int : 4 bytes : -2,147,483,648 to 2,147,483,647 bigint : 8 bytes : -9,223,372,036,854,775,808 to 9,223,372,036,854,775,808 decimal, numeric : 5 – 17 bytes : maximum precision of 38 smallmoney : 4 bytes : -214, to 214, money : 8 bytes : -922,337,203,685, to 922,337,203,685, float : 4 – 8 bytes : approx ± 2 * 10 ±308 real : 4 bytes : approx ± 2 * 10 ±38

8. Numeric Data Type Issues
Float/real are imprecise/approximate • Money has rounding surprises •

9. Precision and Scale of Decimal Operation Results
Result precision
Result scale *
e1 + e2
max(s1, s2) + max(p1-s1, p2-s2) + 1
max(s1, s2)
e1 - e2
e1 * e2
p1 + p2 + 1
s1 + s2
e1 / e2
p1 - s1 + s2 + max(6, s1 + p2 + 1)
max(6, s1 + p2 + 1)
e1 { UNION | EXCEPT | INTERSECT } e2
max(s1, s2) + max(p1-s1, p2-s2)
e1 % e2
min(p1-s1, p2 -s2) + max( s1,s2 )
* The result precision and scale have an absolute maximum of 38. When a result precision is greater than 38, the corresponding scale is reduced to prevent the integral part of a result from being truncated.

10. Numeric Data Type Issues
Float and Real are imprecise/approximate • Money has rounding surprises • More rounding surprises •

11. Character Category
char(N) : N bytes : 8000 characters nchar(N) : 2 * N bytes : 4000 characters varchar(N) : data length + 2 bytes : 8000 characters varchar(MAX) : data length + 2 bytes : ≈ 2,000,000,000 characters nvarchar(N) : 2 * data length + 2 bytes : 4000 characters nvarchar(MAX) : 2 * data length + 2 bytes : ≈1,000,000,000 characters) text : data length : ≈ 2,000,000,000 characters ntext : 2 * data length : ≈ 1,000,000,000 characters

12. Character Category
char(N) : N bytes : 8000 characters nchar(N) : 2 * N bytes : 4000 characters varchar(N) : data length + 2 bytes : 8000 characters varchar(MAX) : data length + 2 bytes : ≈ 2,000,000,000 characters nvarchar(N) : 2 * data length + 2 bytes : 4000 characters nvarchar(MAX) : 2 * data length + 2 bytes : ≈1,000,000,000 characters) text : data length : ≈ 2,000,000,000 characters ntext : 2 * data length : ≈ 1,000,000,000 characters

13. Size Matters (var)char(small) vs. (var)char(big) – difference? •
Domain integrity
(var)char (without specifying size) •
(var)char(n) - When n is not specified in a data definition or variable declaration statement, the default length is 1. When n is not specified with the CAST function, the default length is 30
varchar(n) vs. char(n)
varchar(n) vs. varchar(MAX)
Performance
Rob Garrison blog –

14. Temporal Category
date : 3 bytes : to time : 5 bytes : 00:00: to 23:59: datetime2 : 6 – 8 bytes : to , 100ns precision datetimeoffset : 10 bytes : to , 100ns precision smalldatetime : 4 bytes : to , precision of 1 minute datetime : 8 bytes : to , precision of 3⅓ millisecond (.000, .003, .007, .010 sec)

15. Temporal Category
date : 3 bytes : to time : 5 bytes : 00:00: to 23:59: datetime2 : 6 – 8 bytes : to , 100ns precision datetimeoffset : 10 bytes : to , 100ns precision smalldatetime : 4 bytes : to , precision of 1 minute datetime : 8 bytes : to , precision of 3⅓ millisecond (.000, .003, .007, .010 sec)

16. Temporal Examples Date literals • Using BETWEEN to identify day •
‘1/2/11’?
‘ ’?
‘ ’?
Using BETWEEN to identify day •
Adding days •
What date is 0 or “” (empty string)? •
Eliminating time •

17. Binary Category
binary(N) : N bytes : 8000 bytes varbinary(N) : data length + 2 bytes : 8000 bytes varbinary(MAX) : data length + 2 bytes : ≈ 2,000,000,000 bytes image : ≈ 2,000,000,000 bytes

18. Binary Category
binary(N) : N bytes : 8000 bytes varbinary(N) : data length + 2 bytes : 8000 bytes varbinary(MAX) : data length + 2 bytes : ≈ 2,000,000,000 bytes image : ≈ 2,000,000,000 bytes

19. Other Category
cursor timestamp/rowversion : 8 bytes hierarchyid uniqueidentifier : 16 bytes sql_variant xml table

20. Other Category
cursor timestamp/rowversion : 8 bytes hierarchyid uniqueidentifier : 16 bytes sql_variant xml table

21. Functions ISNUMERIC • TRY_CONVERT / TRY_CAST • ISDATE •
Watch out for empty strings to temporal
ISDATE •
Doesn’t cover entire date range
Doesn’t support full resolution of datetime2
ISNULL vs. COALESCE •
ISNULL returns data type of first argument
COALESCE returns data type of highest precedence
Temporal Functions •
CURRENT_TIMESTAMP
GETDATE()
GETUTCDATE()
SYSDATETIME()
SYSUTCDATETIME()

22. Summary Pick data types with consideration Avoid deprecated data types
Size matters
Domain constraint
Avoid deprecated data types
Beware of implicit conversions
Not SARGable
Unexpected results
Use functions with caution

23. Thanks. Questions?
Vern Rabe
@VernRabe