> ## Documentation Index
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> Use this file to discover all available pages before exploring further.

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

# GenerateRandom table engine

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.

<h2 id="usage-in-clickhouse-server">
  Usage in ClickHouse Server
</h2>

```sql theme={null}
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 or map columns and strings correspondingly in generated data.

Generate table engine supports only `SELECT` queries.

It supports all [DataTypes](/reference/data-types/index) that can be stored in a table except `AggregateFunction`.

<h2 id="example">
  Example
</h2>

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

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

**2.** Query the data:

```sql theme={null}
SELECT * FROM generate_engine_table LIMIT 3
```

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

<h2 id="details-of-implementation">
  Details of Implementation
</h2>

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