SELECT

Basic Syntax

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]

Example:

• View the ClickHouse cluster information.

  select * from system.clusters;

• View the macros set for the node.

  select * from system.macros;

• Check the database capacity.

  select sum(rows) as "Total number of rows", formatReadableSize(sum(data_uncompressed_bytes)) as "Original size", formatReadableSize(sum(data_compressed_bytes)) as "Compression size", round(sum(data_compressed_bytes) / sum(data_uncompressed_bytes) * 100, 0) "Compression rate" from system.parts;

• Query the capacity of the test table. Add and modify the WHERE clause as required.

  select sum(rows) as "Total number of rows", formatReadableSize(sum(data_uncompressed_bytes)) as "Original size", formatReadableSize(sum(data_compressed_bytes)) as "Compression size", round(sum(data_compressed_bytes) / sum(data_uncompressed_bytes) * 100, 0) "Compression rate" from system.parts where table in ('test') and partition like '2020-11-%' group by table;