1. Ouch! Our Data Type Choices Did THAT?
G. Vern Rabe
RabeData, LLC

2. Thank You! local PASS Community & Sponsors!

3. Vern Rabe
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

4. 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

5. Accuracy > Performance > Implicit Conversion (SARGable) >
Why Important?
Accuracy >
Performance >
Implicit Conversion (SARGable) >

6. 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)

7. Data Type Categories
Numeric Character Temporal Binary Other

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

9. Numeric Data Type Issues
Float/real are imprecise/approximate > Money has (early) rounding surprises > More rounding surprises >

10. 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.

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

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

13. Size Matters (var)char(small) vs. (var)char(big) – difference? >
Domain integrity
(var)char vs. (var)char(n) >
(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 : 0001-01-01 to 9999-12-31
time : 00:00: to 23:59:
datetime2 : to , 100ns precision
datetimeoffset : to , 100ns precision
smalldatetime : to , precision of 1 minute
datetime : to , precision of 3⅓ millisecond (.000, .003, .007, .010 sec)

15. Temporal Category date : 0001-01-01 to 9999-12-31
time : 00:00: to 23:59:
datetime2 : to , 100ns precision
datetimeoffset : to , 100ns precision
smalldatetime : to , precision of 1 minute
datetime : to , precision of ~3⅓ millisecond (.000, .003, .007, .010 sec)

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

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

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

19. Other Category
cursor timestamp/rowversion hierarchyid uniqueidentifier sql_variant xml table

20. Other Category
cursor timestamp/rowversion hierarchyid uniqueidentifier sql_variant xml table

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

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?
Contact information
@VernRabe
LinkedIn
References
Don’t use datetime or smalldatetime