# 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;
```