---
description: 'Represents the contents of index and marks files of MergeTree tables.
  It can be used for introspection.'
sidebar_label: 'mergeTreeIndex'
sidebar_position: 77
slug: /sql-reference/table-functions/mergeTreeIndex
title: 'mergeTreeIndex'
---

# mergeTreeIndex Table Function

Represents the contents of index and marks files of MergeTree tables. It can be used for introspection.

## Syntax {#syntax}

```sql
mergeTreeIndex(database, table [, with_marks = true] [, with_minmax = true])
```

## Arguments {#arguments}

| Argument      | Description                                       |
|---------------|---------------------------------------------------|
| `database`    | The database name to read index and marks from.   |
| `table`       | The table name to read index and marks from.      |
| `with_marks`  | Whether include columns with marks to the result. |
| `with_minmax` | Whether include min-max index to the result.      |

## Returned value {#returned_value}

A table object with columns with values of primary index and min-max index (if enabled) of source table, columns with values of marks (if enabled) for all possible files in data parts of source table and virtual columns:

- `part_name` - The name of data part.
- `mark_number` - The number of current mark in data part.
- `rows_in_granule` - The number of rows in current granule.

Marks column may contain `(NULL, NULL)` value in case when column is absent in data part or marks for one of its substreams are not written (e.g. in compact parts).

## Usage Example {#usage-example}

```sql
CREATE TABLE test_table
(
    `id` UInt64,
    `n` UInt64,
    `arr` Array(UInt64)
)
ENGINE = MergeTree
ORDER BY id
SETTINGS index_granularity = 3, min_bytes_for_wide_part = 0, min_rows_for_wide_part = 8;

INSERT INTO test_table SELECT number, number, range(number % 5) FROM numbers(5);

INSERT INTO test_table SELECT number, number, range(number % 5) FROM numbers(10, 10);
```

```sql
SELECT * FROM mergeTreeIndex(currentDatabase(), test_table, with_marks = true);
```

```text
┌─part_name─┬─mark_number─┬─rows_in_granule─┬─id─┬─id.mark─┬─n.mark──┬─arr.size0.mark─┬─arr.mark─┐
│ all_1_1_0 │           0 │               3 │  0 │ (0,0)   │ (42,0)  │ (NULL,NULL)    │ (84,0)   │
│ all_1_1_0 │           1 │               2 │  3 │ (133,0) │ (172,0) │ (NULL,NULL)    │ (211,0)  │
│ all_1_1_0 │           2 │               0 │  4 │ (271,0) │ (271,0) │ (NULL,NULL)    │ (271,0)  │
└───────────┴─────────────┴─────────────────┴────┴─────────┴─────────┴────────────────┴──────────┘
┌─part_name─┬─mark_number─┬─rows_in_granule─┬─id─┬─id.mark─┬─n.mark─┬─arr.size0.mark─┬─arr.mark─┐
│ all_2_2_0 │           0 │               3 │ 10 │ (0,0)   │ (0,0)  │ (0,0)          │ (0,0)    │
│ all_2_2_0 │           1 │               3 │ 13 │ (0,24)  │ (0,24) │ (0,24)         │ (0,24)   │
│ all_2_2_0 │           2 │               3 │ 16 │ (0,48)  │ (0,48) │ (0,48)         │ (0,80)   │
│ all_2_2_0 │           3 │               1 │ 19 │ (0,72)  │ (0,72) │ (0,72)         │ (0,128)  │
│ all_2_2_0 │           4 │               0 │ 19 │ (0,80)  │ (0,80) │ (0,80)         │ (0,160)  │
└───────────┴─────────────┴─────────────────┴────┴─────────┴────────┴────────────────┴──────────┘
```

```sql
DESCRIBE mergeTreeIndex(currentDatabase(), test_table, with_marks = true) SETTINGS describe_compact_output = 1;
```

```text
┌─name────────────┬─type─────────────────────────────────────────────────────────────────────────────────────────────┐
│ part_name       │ String                                                                                           │
│ mark_number     │ UInt64                                                                                           │
│ rows_in_granule │ UInt64                                                                                           │
│ id              │ UInt64                                                                                           │
│ id.mark         │ Tuple(offset_in_compressed_file Nullable(UInt64), offset_in_decompressed_block Nullable(UInt64)) │
│ n.mark          │ Tuple(offset_in_compressed_file Nullable(UInt64), offset_in_decompressed_block Nullable(UInt64)) │
│ arr.size0.mark  │ Tuple(offset_in_compressed_file Nullable(UInt64), offset_in_decompressed_block Nullable(UInt64)) │
│ arr.mark        │ Tuple(offset_in_compressed_file Nullable(UInt64), offset_in_decompressed_block Nullable(UInt64)) │
└─────────────────┴──────────────────────────────────────────────────────────────────────────────────────────────────┘
```
