42.18. pg_index

## 42.18. `pg_index`

The catalog `pg_index` contains part of the information about indexes. The rest is mostly in `pg_class`.

Table 42.18. `pg_index` Columns

Name | Type | References | Description
--- | --- | --- | ---
`indexrelid` | `oid` | ``pg_class`.oid` | The OID of the `pg_class` entry for this index
`indrelid` | `oid` | ``pg_class`.oid` | The OID of the `pg_class` entry for the table this index is for
`indnatts` | `int2` |  | The number of columns in the index (duplicates `pg_class.relnatts`)
`indisunique` | `bool` |  | If true, this is a unique index.
`indisprimary` | `bool` |  | If true, this index represents the primary key of the table. (`indisunique` should always be true when this is true.)
`indisclustered` | `bool` |  | If true, the table was last clustered on this index.
`indkey` | `int2vector` | ``pg_attribute`.attnum` | This is an array of `indnatts` values that indicate which table columns this index indexes. For example a value of `1 3` would mean that the first and the third table columns make up the index key. A zero in this array indicates that the corresponding index attribute is an expression over the table columns, rather than a simple column reference.
`indclass` | `oidvector` | ``pg_opclass`.oid` | For each column in the index key this contains the OID of the operator class to use. See `pg_opclass` for details.
`indexprs` | `text` |  | Expression trees (in `nodeToString()` representation) for index attributes that are not simple column references. This is a list with one element for each zero entry in `indkey`. Null if all index attributes are simple references.
`indpred` | `text` |  | Expression tree (in `nodeToString()` representation) for partial index predicate. Null if not a partial index.