mirror of https://github.com/ClickHouse/ClickHouse.git synced 2024-09-29 21:20:49 +00:00

* CLICKHOUSE-4063: less manual html @ index.md

* CLICKHOUSE-4063: recommend markdown="1" in README.md

* CLICKHOUSE-4003: manually purge custom.css for now

* CLICKHOUSE-4064: expand <details> before any print (including to pdf)

* CLICKHOUSE-3927: rearrange interfaces/formats.md a bit

* CLICKHOUSE-3306: add few http headers

* Remove copy-paste introduced in #3392

* Hopefully better chinese fonts #3392

* get rid of tabs @ custom.css

* Apply comments and patch from #3384

* Add jdbc.md to ToC and some translation, though it still looks badly incomplete

* minor punctuation

* Add some backlinks to official website from mirrors that just blindly take markdown sources

* Do not make fonts extra light

* find . -name '*.md' -type f | xargs -I{} perl -pi -e 's//g' {}

* find . -name '*.md' -type f | xargs -I{} perl -pi -e 's/ sql/g' {}

* Remove outdated stuff from roadmap.md

* Not so light font on front page too

* Refactor Chinese formats.md to match recent changes in other languages

2018-10-16 13:47:17 +03:00

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MySQL

The MySQL engine allows you to perform SELECT queries on data that is stored on a remote MySQL server.

Call format:

MySQL('host:port', 'database', 'table', 'user', 'password'[, replace_query, 'on_duplicate_clause']);

Call parameters

host:port — Address of the MySQL server.
database — Database name on the MySQL server.
table — Name of the table.
user — The MySQL User.
password — User password.
replace_query — Flag that sets query substitution INSERT INTO to REPLACE INTO. If replace_query=1, the query is replaced.
'on_duplicate_clause' — Adds the ON DUPLICATE KEY UPDATE 'on_duplicate_clause' expression to the INSERT query. For example: impression = VALUES(impression) + impression. To specify 'on_duplicate_clause' you need to pass 0 to the replace_query parameter. If you simultaneously pass replace_query = 1 and 'on_duplicate_clause', ClickHouse generates an exception.

At this time, simple WHERE clauses such as =, !=, >, >=, <, <= are executed on the MySQL server.

The rest of the conditions and the LIMIT sampling constraint are executed in ClickHouse only after the query to MySQL finishes.

The MySQL engine does not support the Nullable data type, so when reading data from MySQL tables, NULL is converted to default values for the specified column type (usually 0 or an empty string).

Original article

1.6 KiB Raw Blame History

MySQL

1.6 KiB

Raw Blame History