48 docs tagged with "beginner"

Want to change the default value for new columns in ClickHouse? Here's how to do just that.

Getting the TOO_MANY_SIMULTANEOUS_QUERIES error in ClickHouse? Here's how to analyze which queries are throttling your ClickHouse instance.

Want to explore local files in ClickHouse? Use clickhouse-local to run a temporary ClickHouse instance on your local machine to analyze structured files.

ClickHouse query logs growing too large? Here's how to apply a permanent TTL to your ClickHouse system.query_log.

Want to apply a default value to existing rows in a ClickHouse table column? Here's how to do that with MATERIALIZE.

Getting a TOO_MANY_PARTS exception in ClickHouse? If you see DB::Exception: Too many parts (600), you can avoid it by using async_insert in v21.11.

Want to change table TTLs in ClickHouse? Here's how you can modify the TTL of a table in ClickHouse and avoid impacting performance.

The TTL of a table can be an expression that references one or more columns; this means that the TTL for a given row will be calculated at the point of ingestion.

Ever wanted to create ASCII art from your database? If you're crazy enough to try it, here's how!

Want to know how to create a session when using the ClickHouse HTTP endpoint? Here's how to use the session_id parameter with ClickHouse.

Want to create a ClickHouse table from a remote file URL? You can use the `url` function to do that. Here's how.

Need to detect leap years in ClickHouse? Here's a query to find years that contain 366 days instead of 365.

Dropping large tables in ClickHouse, but exceeding the size limits? Here's how to drop a ClickHouse table over the default 50GB size.

Want to explore data using ClickHouse in the terminal? Here's how to do that with the clickhouse-client command line interface.

Want to post your ClickHouse query results online? Here's how to export your ClickHouse query results to a Markdown table.

Wondering when to use PREWHERE in ClickHouse? Here's how to optimize filtering with PREWHERE and minimize scan size in ClickHouse.

Here's how you can discover which parts & partitions have been detached from your ClickHouse tables.

Are your ClickHouse queries ugly? Here's how to format them in the command line with the ClickHouse query formatter.

ClickHouse servers can open network ports for TCP, HTTP, and gRPC. Here's how to find out which ports these interfaces are bound to on a ClickHouse server.

Want to get the latest ClickHouse build? Here's how to download the latest build to keep up with the many changes to ClickHouse.

Curious to know your ClickHouse server temperature? Here's a query to get your ClickHouse server temperature.

Wondering what version of ClickHouse you're running? Here's how to get your ClickHouse version with a query, in the CLI, or over the HTTP interface.

ClickHouse doesn't perform overflow checks when casting between integer types. Here's how to handle integer overflows in ClickHouse with accurateCast.

Getting errors trying to cast toDateTime in ClickHouse? Use this ClickHouse function to handle most DateTime variations without throwing an exception.

Want to drop a table in ClickHouse without waiting until it's deleted? Here's how to use the SYNC modifier to drop tables synchronously in ClickHouse.

Does the order of ClickHouse sorting keys affect performance? Read this to learn the answer.

Does the order of your GROUP BY in ClickHouse affect query performance? Read this to learn why GROUP BY order matters.

Wondering how to benchmark functions in ClickHouse? Here are a bunch of tips to help you better benchmark your functions in ClickHouse.

Ever wonderered how to calculate year over year growth in ClickHouse? Read this to learn how it's done.

ClickHouse has many unique data types. Here's how to choose the right ones for your tables.

Wondering how to configure ClickHouse settings? Here are 5 tips to take into account when doing so.

Want to infer the table schema of a remote file using ClickHouse? Here's how to do that with DESCRIBE TABLE.

Sometimes you want ClickHouse materialized views to behave like a typical RDBMS. Here's how to use Live Views to periodically refresh ClickHouse materializations.

Want to speed up your joins in ClickHouse? Here is a smart approach to improving ClickHouse join speed by applying your filters earlier in a subquery.

Wondering how to monitor your ClickHouse server for new errors? Use the system.errors table to track all errors since the server started.

Sum() and Count() are the most common ClickHouse aggregations. Here's how to speed up queries in ClickHouse that use a sum and count aggregation.

Want to optimize your queries in ClickHouse? Here's how to use column compression to speed up ClickHouse queries.

Wondering how to optimize single row joins in ClickHouse? Use a CROSS JOIN to improve join efficiency in ClickHouse.

Sometimes you need to parse complex emojis in your ClickHouse queries. Here's how to do that with the ClickHouse tokens() function.

Parsing URLs with SQL can be a pain. Here's how to use ClickHouse functions to work with URLs and avoid writing custom Regex.

Want to get data from multiple tables in ClickHouse with a single query? Use the merge() ClickHouse function instead of UNION ALL for cleaner queries.

Trying to debug a problem with your ClickHouse query, but having trouble filtering through the log file? Here's how to show logs in the CLI to reduce noise when debugging ClickHouse.

Want to drop a table in ClickHouse, but worried about losing data? Here's how to "soft" delete a ClickHouse table so you can restore it in the future.

ClickHouse currently is not able to use the knowledge of the sort key from a table to speed up aggregations. This means that to get the ARGMIN() or ARGMAX() values from a table it will read all values even if it's sorted by that column:

Working with datetimes in ClickHouse? Here's how to subtract values from two DateTime64 columns in a ClickHouse table without getting an error.

Want to swap one table for another in ClickHouse? Here are two ways to swap tables in ClickHouse using EXCHANGE TABLE or RENAME TABLE statements

Trying to parse a specific ClickHouse error code? Here's how to view all error codes in ClickHouse.

Wondering the difference between the -If combinator and the WHERE statement in ClickHouse? Here are some guidelines to help you choose between -If and WHERE in ClickHouse.