ClickHouse/docs/en/operations/table_engines/generate.md

# GenerateRandom {#table_engines-generate}

The GenerateRandom table engine produces random data for given table schema.

Usage examples:

-   Use in test to populate reproducible large table.
-   Generate random input for fuzzing tests.

## Usage in ClickHouse Server {#usage-in-clickhouse-server}

``` sql
ENGINE = GenerateRandom(random_seed, max_string_length, max_array_length)
```

The `max_array_length` and `max_string_length` parameters specify maximum length of all
array columns and strings correspondingly in generated data.

Generate table engine supports only `SELECT` queries.

It supports all [DataTypes](../../data_types/index.md) that can be stored in a table except `LowCardinality` and `AggregateFunction`.

**Example:**

**1.** Set up the `generate_engine_table` table:

``` sql
CREATE TABLE generate_engine_table (name String, value UInt32) ENGINE = GenerateRandom(1, 5, 3)
```

**2.** Query the data:

``` sql
SELECT * FROM generate_engine_table LIMIT 3
```

``` text
┌─name─┬──────value─┐
│ c4xJ │ 1412771199 │
│ r    │ 1791099446 │
│ 7#$  │  124312908 │
└──────┴────────────┘
```

## Details of Implementation {#details-of-implementation}

-   Not supported:
    -   `ALTER`
    -   `SELECT ... SAMPLE`
    -   `INSERT`
    -   Indices
    -   Replication

[Original article](https://clickhouse.tech/docs/en/operations/table_engines/generate/) <!--hide-->