1.1 KiB
MySQL
The MySQL engine allows you to perform SELECT queries on data that is stored on a remote MySQL server.
The engine takes 5-7 parameters: the server address (host and port); the name of the database; the name of the table; the user's name; the user's password; whether to use replace query; the on duplcate clause. Example:
MySQL('host:port', 'database', 'table', 'user', 'password'[, replace_query, 'on_duplicate_clause']);
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.
If replace_query is specified to 1, then INSERT INTO query to this table would be transformed to REPLACE INTO.
If on_duplicate_clause is specified, eg update impression = values(impression) + impression, it would add on_duplicate_clause to the end of the MySQL insert sql.
Notice that only one of 'replace_query' and 'on_duplicate_clause' can be specified, or none of them.