March 2021
Intermediate to advanced
265 pages
6h 50m
Chinese
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138
｜
第
8
章
WHERE
子句的条件由一个或多个布尔表达式组成，这些表达式由
AND
和
OR
相连。
SELECT custkey, acctbal
FROM tpch.sf1.customer WHERE acctbal < 0;
custkey | acctbal
---------+---------
75016 | -735.89
75027 | -399.78
75028 | -222.92
75034 | -679.38
75037 | -660.07
...
SELECT custkey, acctbal FROM tpch.sf1.customer
WHERE acctbal > 0 AND acctbal < 500;
custkey | acctbal
---------+---------
75011 | 165.71
75012 | 41.65
75021 | 176.2
75022 | 348.24
75026 | 78.64
75084 | 18.68
75107 | 314.88
...
WHERE
子句的条件很重要，因为它可用于多种查询优化。在
4.8
节中，你可以了解更多关
于查询优化的内容。当查询多个表时，你可以通过
WHERE
子句中的条件将它们连接起来。
Presto
使用这些信息来决定高效的查询执行计划。
8.12
GROUP BY
和
HAVING
子句
GROUP BY
和
HAVING
子句在分析型查询中非常常用。
GROUP BY
用于将具有相同值的行合并 ...