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问题描述

id name types
1 dashboard_trunk dashboard
2 monkey_trunk monkey
3 dashboard_projects_10_9_9 dashboard
4 performance_trunk
5 performance_projects_10_9_8 performance

原因追溯

• NULL is used as a placeholder for unknown or inapplicable values, it is treated differently from other values.
• It is not possible to test for NULL values with comparison operators, such as =, <, or <>. We will have to use the IS NULL and IS NOT NULL operators instead.

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