PostgreSQL 7.4.11 Documentation
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# 43.8. `pg_cast`

The catalog `pg_cast` stores data type conversion paths, both built-in paths and those defined with `CREATE CAST`.

Table 43-8. `pg_cast` Columns

Name | Type | References | Description
--- | --- | --- | ---
`castsource` | `oid` | ``pg_type`.oid` | OID of the source data type
`casttarget` | `oid` | ``pg_type`.oid` | OID of the target data type
`castfunc` | `oid` | ``pg_proc`.oid` | The OID of the function to use to perform this cast. Zero is stored if the data types are binary compatible (that is, no run-time operation is needed to perform the cast).
`castcontext` | `char` |  | Indicates what contexts the cast may be invoked in. `e` means only as an explicit cast (using `CAST`, `::`, or function-call syntax). `a` means implicitly in assignment to a target column, as well as explicitly. `i` means implicitly in expressions, as well as the other cases.

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