UNION vs UNION ALL from a performance viewpoint

UNION vs UNION ALL from a performance viewpoint

题目类型: 技术面试题

这是一道技术面试题，常见于澳洲IT公司面试中。

难度: medium

标签: interviewbit, dbms, topic-specific, database

参考答案摘要

UNION combines results from multiple queries and removes duplicate rows from the final output. To do this, the database has to sort and compare rows, which takes extra time. UNION ALL simply appends t...

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