pg_index

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

Table 1. pg_catalog.pg_index

column	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`	smallint		The number of columns in the index (duplicates `pg_class.relnatts`).
`indisunique`	boolean		If true, this is a unique index.
`indisclustered`	boolean		If true, the table was last clustered on this index via the `CLUSTER` command.
`indisvalid`	boolean		If true, the index is currently valid for queries. False means the index is possibly incomplete: it must still be modified by `INSERT` operations, but it cannot safely be used for queries.
`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.
`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.