SYSTEM CATALOG · 系统目录

pg_cast

The catalog pg_cast stores data type conversion paths, both built-in and user-defined. It should be noted that pg_cast does not represent every type conversion that the system knows how to perform; only those that cannot be deduced from some generic rule. For example, casting between a domain and its base type is not explicitly represented in pg_cast. Another important exception is that “automatic I/O conversion casts”, those performed using a data type's own I/O functions to convert to or from text or other string types, are not explicitly represented in pg_cast.

首次收录 PG 9.0最近收录 PG 19当前字段 6

9.0 9.1 9.2 9.3 9.4 9.5 9.6 10 11 12 13 14 15 16 17 18 19^β3

已与 PostgreSQL 18.6 实例逐字段核对 · 原始实测记录 ↗

字段结构 PostgreSQL 18

pg_cast

字段 / COLUMN	类型 / TYPE	说明 / DESCRIPTION
`oid`	`oid`NOT NULL	Row identifier
`castsource`	`oid`NOT NULL	OID of the source data type引用：`pg_type.oid`
`casttarget`	`oid`NOT NULL	OID of the target data type引用：`pg_type.oid`
`castfunc`	`oid`NOT NULL	The OID of the function to use to perform this cast. Zero is stored if the cast method doesn't require a function.引用：`pg_proc.oid`
`castcontext`	`"char"`NOT NULL文档原写法：`char`	Indicates what contexts the cast can be invoked in. e means only as an explicit cast (using CAST or :: 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.
`castmethod`	`"char"`NOT NULL文档原写法：`char`	Indicates how the cast is performed. f means that the function specified in the castfunc field is used. i means that the input/output functions are used. b means that the types are binary-coercible, thus no conversion is required.

标记“隐式列”的字段不包含在 SELECT * 中；部分早期统计视图由同版本源码补全，额外来源会显示在字段说明中。

通用系统列 6

PostgreSQL 提供的系统属性，通常不在 SELECT * 中展开。单独保留，不与普通字段混算。

字段	类型	attnum
`tableoid`	`oid`	-6
`cmax`	`cid`	-5
`xmax`	`xid`	-4
`cmin`	`cid`	-3
`xmin`	`xid`	-2
`ctid`	`tid`	-1

字段演化矩阵

悬停查看字段类型

存在新增 / 类型或属性变化移除

字段 / COLUMN	9.0	9.1	9.2	9.3	9.4	9.5	9.6	10	11	12	13	14	15	16	17	18	19
`oid`
`castsource`
`casttarget`
`castfunc`
`castcontext`
`castmethod`

9.0 是收录基线；基线中已存在的字段不标记为新增。矩阵按字段名称对齐，重命名显示为旧字段移除与新字段新增。

演化时间线

相邻大版本的变化

PostgreSQL 12 ← 11

~ oid: 隐式列 → 常规列1 处字段说明更新

PostgreSQL 10 ← 9.6

目录说明更新

PostgreSQL 9.3 ← 9.2

1 处字段说明更新

PostgreSQL 9.2 ← 9.1

目录说明更新

比较任意两个版本

起始版本 / FROM目标版本 / TO包含描述更新

选择两个版本，查看字段的新增、移除与类型变化。交互比较需要 JavaScript；演化时间线可直接阅读。