更新时间:2022-05-19 GMT+08:00
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SELECT查询表数据

本章节主要介绍ClickHouse查询表数据的SQL基本语法和使用说明。

基本语法

SELECT [DISTINCT] expr_list

[FROM [database_name.]table | (subquery) | table_function] [FINAL]

[SAMPLE sample_coeff]

[ARRAY JOIN ...]

[GLOBAL] [ANY|ALL|ASOF] [INNER|LEFT|RIGHT|FULL|CROSS] [OUTER|SEMI|ANTI] JOIN (subquery)|table (ON <expr_list>)|(USING <column_list>)

[PREWHERE expr]

[WHERE expr]

[GROUP BY expr_list] [WITH TOTALS]

[HAVING expr]

[ORDER BY expr_list] [WITH FILL] [FROM expr] [TO expr] [STEP expr]

[LIMIT [offset_value, ]n BY columns]

[LIMIT [n, ]m] [WITH TIES]

[UNION ALL ...]

[INTO OUTFILE filename]

[FORMAT format]

使用示例

--查看ClickHouse集群信息
select * from system.clusters;
--显示当前节点设置的宏
select * from system.macros;
--查看数据库容量
select
sum(rows) as "总行数",
formatReadableSize(sum(data_uncompressed_bytes)) as "原始大小",
formatReadableSize(sum(data_compressed_bytes)) as "压缩大小",
round(sum(data_compressed_bytes) / sum(data_uncompressed_bytes) * 100,
0) "压缩率"
from system.parts;
--查询test表容量。where条件根据实际情况添加修改
select
sum(rows) as "总行数",
formatReadableSize(sum(data_uncompressed_bytes)) as "原始大小",
formatReadableSize(sum(data_compressed_bytes)) as "压缩大小",
round(sum(data_compressed_bytes) / sum(data_uncompressed_bytes) * 100,
0) "压缩率"
from system.parts
where table in ('test')
and partition like '2020-11-%'
group by table;
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