June 2010
Intermediate to advanced
328 pages
7h 51m
English
Content preview from SQL Antipatterns
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Antipattern: Create Multiple Columns
We still have to account for multiple values in the attribute, but we know the new solution must store only a single value in each column. It might seem natural to create multiple columns in this table, each containing a single tag.
| Multi-Column/anti/create-table.sql | |
| | CREATE TABLE Bugs ( |
| | bug_id SERIAL PRIMARY KEY, |
| | description VARCHAR(1000), |
| | tag1 VARCHAR(20), |
| | tag2 VARCHAR(20), |
| | tag3 VARCHAR(20) |
| | ); |
As you assign tags to a given bug, you’d put values in one of these three columns. Unused columns remain null.
| Multi-Column/anti/update.sql | |
| | UPDATE Bugs SET tag2 = 'performance' WHERE bug_id = 3456; |
bug_id | description | tag1 | tag2 | tag3 |
|---|---|---|---|---|
1234 | Crashes while saving | crash | NULL | NULL |
3456 | Increase performance ... |
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