Database Design: Solving Problems Before they Start! Ed Pollack Database Administrator CommerceHub

Agenda Preventing future headaches, right now! Why does database design matter to us? Discussion of tables. Examples of good design practices. Important decisions when designing a database. Notes on important database design topics. Normalization Conclusion 2

Why Design Matters Match business needs with implementation. Ensure acceptable performance. Scalability. Needs of tomorrow != Needs of today. Good design = easy to understand. Decrease maintenance costs. Avoid scorn of future DBAs & developers. 3

Understand the Application Good design = knowing the business need. Talk to consumers of data. Ask lots of questions! May be technical or non-technical. What is the database used for? 4

Scalability Design for today AND tomorrow. Understand cardinality. Determine contention and concurrency. Build overhead to support the near future. Always re-evaluate and ensure scalability for the future. 5

Hardware Considerations CPU (speed, cores, MDOP, etc…) Memory Storage (attached, SAN, SSD, cloud, etc…) Network bandwidth On-premises vs. cloud File & backup locations 6

Designing Good Tables One table = a distinct entity. A column represents a unique element. Table can be one of three basic types: Entity Lookup Relationship (linking) Schemas can classify name spaces/security/classification. Avoid “double-duty” tables!!! 7

Data Types Choose the correct data type. Choose the correct data length/precision/size. Consider standards when unsure of representation Ie: ISO5218 for gender, ISO4217 for currency, ISO3166 for country Bit = 1 or 0. Do not use INT, string, etc… Consider mathematical operations for numeric types. 8

Dates & Times Be consistent across all tables! Do (or will) time zones matter? If so, use DATETIMEOFFSET or UTC time. Store in correct sized data type. Smalldatetime vs. Datetime2 vs. Date vs. Time Do not use strings for dates, times, timestamps, etc... Differentiate between a date/time and duration. 9

NULL vs. NOT NULL NULL = non-existence. Do not make up “De-nullifiers”. -1, 1/1/1900, ‘N/A’, ‘ ‘, ‘00:00’ NOT NULL = required by the application NULL has meaning. Define this during design phase. Beware NULL behavior. ORDER BY, GROUP BY, =, <>…\ Always explicitly name ALL objects! 10

Naming Objects What is it? Don’t name for location, time, usage, etc… A data element name should be unique! Column names should be positive, not negative Ie: Is_Not_Active vs. Is_Active Avoid abbreviations/shorthand. Don’t fear long names. Avoid spaces and special characters. DOCUMENTATION!!! 11

Uniqueness All rows in a table should be unique. PRIMARY KEY determines row identity/uniqueness. Natural key vs. surrogate key. Clustered key doesn’t have to be the primary key, but often will be. Unique constraints can enforce additional important business rules. 12

Other Schema Elements Stored Procedures: Use for efficient/controlled data access. Indexes: Speed up important read operations. Functions*: Encapsulate often-used logic. Triggers*: Enforce auditing, ETL, or business rules. Constraints*: Enforce important relationships/rules. Views: Provide a convenient/common path to data. ***Always ensure elements are needed before creation! 13

Iteration vs. Set-Based Operations SQL Server is built/optimized set-based transactions. Use of loops, such as CURSOR, WHILE, GOTO are often indicative of poor/suboptimal design. Consider alternatives to avoid row-by-row work: OUTPUT Window functions CTE 14

OLAP vs. OLTP The needs of transactional processing are different than the needs of analytics processing. Separate reporting from transactional processing, or build infrastructure to support a shared environment. Denormalize data for OLAP, not for OLTP. Consider different tools for each, if needed. 15

Old Data Do we delete, inactivate, partition, archive, etc…? Is archiving allowed/desired/required? How to handle data associated with archived data? Data retention policy Compliance needs. Contractual obligations. Prevent data from getting too large 16

Normalization Normalization reduces data redundancy by separation into tables. Avoids inconsistency via duplicated/missing/bad data. Consider 1:1 vs. 1:many vs. many:many vs. optional. DEMO: Normal forms. 17

Formatting Databases store and return data Formatting/presentation is best left to the application. Formatting can complicate scripts. Making output pretty can lead to poor performing queries. Be consistent across all objects! 18

Conclusion Good database design saves immense time & effort. Generates database schema that is easy to understand. Allows for easier upgrades, releases, migrations. Poor design = technical debt! Future DBAs and developers will see your initials and love you! 19

Questions???

Contact Info & Links Ed SQL Shack SQL Server Central SQL Saturday Albany (2016) Thank you!!!