Queries & Syntax

GROUP BY

Learn about the GROUP BY clause in ClickHouse®

Adjustable table partitioning

An approach that allows you to redefine partitioning without table creation

DateTime64

DISTINCT & GROUP BY & LIMIT 1 BY what the difference

Imprecise parsing of literal Decimal or Float64

Multiple aligned date columns in PARTITION BY expression

How to put multiple correlated date-like columns in partition key without generating a lot of partitions in case not exact match between them.

Row policies overhead (hiding 'removed' tenants)

One more approach to hide (delete) rows in ClickHouse®

Why is simple `SELECT count()` Slow in ClickHouse®?

Collecting query execution flamegraphs using system.trace_log

Using array functions to mimic window-functions alike behavior

-State & -Merge combinators

ALTER MODIFY COLUMN is stuck, the column is inaccessible.

ANSI SQL mode

Async INSERTs

Atomic insert

Cumulative Anything

Data types on disk and in RAM

DELETE via tombstone column

EXPLAIN query

Fill missing values at query time

FINAL clause speed

Join with Calendar using Arrays

JOINs

JSONExtract to parse many attributes at a time

KILL QUERY

Lag / Lead

Machine learning in ClickHouse

Mutations

ALTER UPDATE / DELETE

OPTIMIZE vs OPTIMIZE FINAL

Parameterized views

Use both projection and raw data in single query

How to write queries, which will use both data from projection and raw table.

PIVOT / UNPIVOT

Possible deadlock avoided. Client should retry

Projections

Roaring bitmaps for calculating retention

SAMPLE by

Sampling Example

Simple aggregate functions & combinators

Skip indexes

Time zones

Time-series alignment with interpolation

Top N & Remain

Troubleshooting

Tips for ClickHouse® troubleshooting

TTL

UPDATE via Dictionary

Values mapping

Window functions