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docs/en/operations/named-collections.md
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docs/en/operations/named-collections.md
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---
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sidebar_position: 69
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sidebar_label: "Named connections"
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---
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# Storing details for connecting to external sources in configuration files {#named-collections}
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Details for connecting to external sources (dictionaries, tables, table functions) can be saved
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in configuration files and thus simplify the creation of objects and hide credentials
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from users with only SQL access.
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Parameters can be set in XML `<format>CSV</format>` and overridden in SQL `, format = 'TSV'`.
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The parameters in SQL can be overridden using format `key` = `value`: `compression_method = 'gzip'`.
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Named connections are stored in the `config.xml` file of the ClickHouse server in the `<named_collections>` section and are applied when ClickHouse starts.
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Example of configuration:
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```xml
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$ cat /etc/clickhouse-server/config.d/named_collections.xml
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<clickhouse>
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<named_collections>
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...
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</named_collections>
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</clickhouse>
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```
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## Named connections for accessing S3.
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The description of parameters see [s3 Table Function](../sql-reference/table-functions/s3.md).
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Example of configuration:
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```xml
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<clickhouse>
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<named_collections>
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<s3_mydata>
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<access_key_id>AKIAIOSFODNN7EXAMPLE</access_key_id>
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<secret_access_key> wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY</secret_access_key>
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<format>CSV</format>
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<url>https://s3.us-east-1.amazonaws.com/yourbucket/mydata/</url>
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</s3_mydata>
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</named_collections>
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</clickhouse>
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```
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### Example of using named connections with the s3 function
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```sql
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INSERT INTO FUNCTION s3(s3_mydata, filename = 'test_file.tsv.gz',
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format = 'TSV', structure = 'number UInt64', compression_method = 'gzip')
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SELECT * FROM numbers(10000);
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SELECT count()
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FROM s3(s3_mydata, filename = 'test_file.tsv.gz')
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┌─count()─┐
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│ 10000 │
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└─────────┘
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1 rows in set. Elapsed: 0.279 sec. Processed 10.00 thousand rows, 90.00 KB (35.78 thousand rows/s., 322.02 KB/s.)
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```
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### Example of using named connections with an S3 table
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```sql
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CREATE TABLE s3_engine_table (number Int64)
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ENGINE=S3(s3_mydata, url='https://s3.us-east-1.amazonaws.com/yourbucket/mydata/test_file.tsv.gz', format = 'TSV')
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SETTINGS input_format_with_names_use_header = 0;
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SELECT * FROM s3_engine_table LIMIT 3;
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┌─number─┐
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│ 0 │
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│ 1 │
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│ 2 │
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└────────┘
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```
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## Named connections for accessing MySQL database
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The description of parameters see [mysql](../sql-reference/table-functions/mysql.md).
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Example of configuration:
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```xml
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<clickhouse>
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<named_collections>
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<mymysql>
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<user>myuser</user>
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<password>mypass</password>
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<host>127.0.0.1</host>
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<port>3306</port>
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<database>test</database>
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<connection_pool_size>8</connection_pool_size>
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<on_duplicate_clause>1</on_duplicate_clause>
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<replace_query>1</replace_query>
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</mymysql>
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</named_collections>
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</clickhouse>
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```
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### Example of using named connections with the mysql function
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```sql
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SELECT count() FROM mysql(mymysql, table = 'test');
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┌─count()─┐
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│ 3 │
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└─────────┘
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```
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### Example of using named connections with an MySQL table
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```sql
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CREATE TABLE mytable(A Int64) ENGINE = MySQL(mymysql, table = 'test', connection_pool_size=3, replace_query=0);
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SELECT count() FROM mytable;
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┌─count()─┐
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│ 3 │
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└─────────┘
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```
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### Example of using named connections with database with engine MySQL
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```sql
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CREATE DATABASE mydatabase ENGINE = MySQL(mymysql);
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SHOW TABLES FROM mydatabase;
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┌─name───┐
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│ source │
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│ test │
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└────────┘
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```
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### Example of using named connections with an external dictionary with source MySQL
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```sql
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CREATE DICTIONARY dict (A Int64, B String)
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PRIMARY KEY A
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SOURCE(MYSQL(NAME mymysql TABLE 'source'))
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LIFETIME(MIN 1 MAX 2)
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LAYOUT(HASHED());
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SELECT dictGet('dict', 'B', 2);
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┌─dictGet('dict', 'B', 2)─┐
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│ two │
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└─────────────────────────┘
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```
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## Named connections for accessing PostgreSQL database
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The description of parameters see [postgresql](../sql-reference/table-functions/postgresql.md).
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Example of configuration:
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```xml
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<clickhouse>
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<named_collections>
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<mypg>
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<user>pguser</user>
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<password>jw8s0F4</password>
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<host>127.0.0.1</host>
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<port>5432</port>
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<database>test</database>
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<schema>test_schema</schema>
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<connection_pool_size>8</connection_pool_size>
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</mypg>
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</named_collections>
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</clickhouse>
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```
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### Example of using named connections with the postgresql function
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```sql
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SELECT * FROM postgresql(mypg, table = 'test');
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┌─a─┬─b───┐
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│ 2 │ two │
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│ 1 │ one │
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└───┴─────┘
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SELECT * FROM postgresql(mypg, table = 'test', schema = 'public');
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┌─a─┐
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│ 1 │
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│ 2 │
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│ 3 │
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└───┘
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```
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### Example of using named connections with database with engine PostgreSQL
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```sql
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CREATE TABLE mypgtable (a Int64) ENGINE = PostgreSQL(mypg, table = 'test', schema = 'public');
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SELECT * FROM mypgtable;
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┌─a─┐
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│ 1 │
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│ 2 │
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│ 3 │
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└───┘
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```
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### Example of using named connections with database with engine PostgreSQL
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```sql
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CREATE DATABASE mydatabase ENGINE = PostgreSQL(mypg);
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SHOW TABLES FROM mydatabase
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┌─name─┐
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│ test │
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└──────┘
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```
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### Example of using named connections with an external dictionary with source POSTGRESQL
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```sql
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CREATE DICTIONARY dict (a Int64, b String)
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PRIMARY KEY a
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SOURCE(POSTGRESQL(NAME mypg TABLE test))
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LIFETIME(MIN 1 MAX 2)
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LAYOUT(HASHED());
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SELECT dictGet('dict', 'b', 2);
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┌─dictGet('dict', 'b', 2)─┐
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│ two │
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└─────────────────────────┘
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```
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@ -116,7 +116,7 @@ In addition, this column is not substituted when using an asterisk in a SELECT q
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`EPHEMERAL expr`
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Ephemeral column. Such a column isn't stored in the table and cannot be SELECTed, but can be referenced in the defaults of CREATE statement.
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Ephemeral column. Such a column isn't stored in the table and cannot be SELECTed, but can be referenced in the defaults of CREATE statement. If `expr` is omitted type for column is required.
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INSERT without list of columns will skip such column, so SELECT/INSERT invariant is preserved - the dump obtained using `SELECT *` can be inserted back into the table using INSERT without specifying the list of columns.
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### ALIAS {#alias}
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