55.8. `pg_attrmask`
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## 55.8. `pg_attrmask`

The catalog `pg_attrmask` stores column masking expressions. The main information about columns is stored in `pg_attribute`. Only columns for which a masking expression has been explicitly set will have an entry here.

Table 55.8. `pg_attrmask` Columns

Column Type Description
`oid` `oid` Row identifier
`amrelid` `oid` (references `pg_class`.`oid`) The table this expression belongs to
`amnum` `int2` (references `pg_attribute`.`attnum`) The number of the column
`ambin` `pg_node_tree` The column masking expression value, in `nodeToString()` representation. Use `pg_get_expr(ambin, amrelid)` to convert it to an SQL expression.

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