sql server data types choosing and using

G. Vern Rabe - [email protected] 1

SQL Server Data TypesChoosing and Using

2012-09-12


Vern Rabe

• Independent consultant, trainer• MCT, MCDBA, MCSE, MCITP• SQL Server Pro magazine advisory board• Oregon PASS Steering Committee• Working with/focusing on SQL Server since

1993, starting with SQL Server 4.21a

2012-09-12


Data TypesWhat We’ll Cover

• Why do we care?– Performance, accuracy

• Data type by Data type– When to use which

• Functions and Nuggets– What to use, what not to use, some workarounds

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Why Important?

• Performance

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Implicit ConversionData Type Precedence

16. int17. smallint18. tinyint19. bit20. ntext21. text22. image23. rownumber24. uniqueidentifier25. nvarchar26. nchar27. varchar28. char29. varbinary30. binary (lowest)

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1. user-defined data types (highest)2. sql_variant3. xml4. datetimeoffset5. datetime26. datetime7. smalldatetime8. date9. time10. float11. real12. decimal13. money14. smallmoney15. bigint


Why Important?

• Performance

• Accuracy

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Data Type Categories

• Number• Character• Temporal• Binary• Other

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Number 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 : -214,748.3648 to 214,748.3647• money : -922,337,203,685,477.5808 to 922,337,203,685,477.5807• float : approx ± 2 * 10 ±308

• real : approx ± 2 * 10 ±38

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Numeric Data Type Issues

• Float is imprecise/approximate

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Numeric Data Type Issues

• Float is imprecise/approximate• Money has rounding surprises• Know your decimal limits (operator results)

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Precision and Scale ofDecimal Operation Results

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Operation Result precision Result scale *

e1 + e2 max(s1, s2) + max(p1-s1, p2-s2) + 1 max(s1, s2)

e1 - e2 max(s1, s2) + max(p1-s1, p2-s2) + 1 max(s1, s2)

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) max(s1, s2)

e1 % e2 min(p1-s1, p2 -s2) + max( s1,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.


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 characters2012-09-12


Size Matters• (var)char(small) vs. (var)char(big) – difference? • (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 – http

://www.simple-talk.com/sql/database-administration/whats-the-point-of-using-varchar(n)-anymore/

– Domain integrity2012-09-12

http://www.simple-talk.com/sql/database-administration/whats-the-point-of-using-varchar(n)-anymore/





Temporal Category

• date : 0001-01-01 to 9999-12-31• time : 00:00:00.0000000 to 23:59:59.9999999• datetime2 : 0001-01-01 to 9999-12-31, 100ns precision• datetimeoffset : 0001-01-01 to 9999-12-31, 100ns

precision• smalldatetime : 1900-01-01 to 2079-06-06, precision

of 1 minute• datetime : 1753-01-01 to 9999-12-31, precision of 3⅓

millisecond (.000, .003, .007, .010 sec)

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Temporal Examples

• Date literals– ‘1/2/11’?– ‘01-02-2011’?– ‘2011-01-02’?

• Using BETWEEN to identify day• Adding days

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Binary Category

• binary(N) : 8000 bytes• varbinary(N) : 8000 bytes• varbinary(MAX) ≈ 2,000,000,000 bytes• image : ≈ 2,000,000,000 bytes

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Other Category

• cursor• timestamp/rowversion• hierarchyid• uniqueidentifier• sql_variant• xml• table

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Functions

• ISNUMERIC• TRY_CONVERT• ISDATE

– Doesn’t cover entire date range– Doesn’t support 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

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Thanks

• Questions?

• Contact information– [email protected]– LinkedIn• www.linkedin.com/pub/vern-rabe/a/ba3/980

2012-09-12

mailto:[email protected]

sql server data types choosing and using

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