How to Create a ClickHouse Dictionary with String Keys and Values

Learn how to create a ClickHouse dictionary using string keys and values from a MergeTree table as the source, with examples of setup and usage.

Question

How to create a ClickHouse dictionary using string keys and string values from a MergeTree table source

Answer

• Create the source table for the dictionary

CREATE TABLE db1.table1_dict_source
(
  id UInt32,
  email String,
  name String
)
ENGINE = MergeTree()
ORDER BY id;

• Insert rows

INSERT INTO db1.table1_dict_source
(id, email, name)
VALUES
(1, '[e-mail]', 'me'),
(2, '[e-mail]', 'you');

• Create dictionary with key/value both as String

CREATE DICTIONARY db1.table1_dict
(
    email String,
    name String
)
PRIMARY KEY email
SOURCE(
CLICKHOUSE(
TABLE 'table1_dict_source'
USER 'default'
PASSWORD 'ClickHouse123!'))
LAYOUT(COMPLEX_KEY_HASHED())
LIFETIME(MIN 0 MAX 1000);

• Test the dictionary

clickhouse-cloud :) SELECT * from db1.table1_dict;

SELECT *
FROM db1.table1_dict

Query id: 098396ce-11dd-4c71-a0e1-40723dd67ddc

┌─email──────────┬─name─┐
│ [e-mail]  │ me   │
│ [e-mail] │ you  │
└────────────────┴──────┘

2 rows in set. Elapsed: 0.001 sec. 

You can also use dictGet function to retrieve values from it such as:

SELECT dictGet('db1.table1_dict', 'name', '[e-mail]');

Response:

┌─dictGet('db1.table1_dict', 'name', '[e-mail]')─┐
│ me                                                  │
└─────────────────────────────────────────────────────┘

More details - https://clickhouse.com/docs/sql-reference/functions/ext-dict-functions