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support rebuild-view-after-column-type-changed
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‎CN/modules/ROOT/nav.adoc‎

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* IvorySQL试验田
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** xref:v1.17/41.adoc[1、全局唯一索引]
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** xref:v1.17/42.adoc[2、新增无主键表默认支持逻辑复制]
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** xref:v1.17/43.adoc[3、修改列类型时自动重建依赖视图]
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* xref:v1.17/20.adoc[社区贡献指南]
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* xref:v1.17/21.adoc[工具参考]
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* xref:v1.17/22.adoc[FAQ]

‎CN/modules/ROOT/pages/v1.17/43.adoc‎

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:sectnums:
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:sectnumlevels: 5
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:imagesdir: ./_images
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= 修改列类型时自动重建依赖视图
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== 功能介绍
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在标准 PostgreSQL 中，若某列被视图所引用，执行 `ALTER TABLE ... ALTER COLUMN ... TYPE` 修改该列的数据类型时，数据库会直接报错：
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----
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ERROR: cannot alter type of a column used by a view or rule
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----
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用户必须手动删除所有依赖视图，完成列类型修改后再逐一重建，操作繁琐且容易出错，在存在多层视图依赖时尤为困难。
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IvorySQL 对此行为进行了增强：执行列类型变更时，数据库会自动保存所有依赖视图（包括间接依赖的级联视图）的定义，在完成类型修改后按正确顺序重建这些视图
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，对用户完全透明。若重建过程中发生错误（例如视图使用了新类型不支持的操作符），整个 `ALTER TABLE` 操作将整体回滚，保证数据一致性。
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该功能同时支持 PG 兼容模式与 Oracle 兼容模式。
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== 语法
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语法与标准 `ALTER TABLE` 完全一致，无需额外关键字：
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[source,sql]
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----
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ALTER TABLE table_name ALTER COLUMN column_name TYPE new_type;
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----
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参数说明：
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- `table_name`：目标表名，可带 schema 前缀；
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- `column_name`：需要修改类型的列名；
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- `new_type`：目标数据类型，需与原类型兼容或可隐式转换。
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== 测试用例
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=== 单视图依赖：自动重建
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[source,sql]
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----
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-- 创建基表
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CREATE TABLE t (a int, b text);
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-- 创建依赖列 a 的视图
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CREATE VIEW v AS SELECT a, b FROM t;
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-- 标准 PostgreSQL 此处会报错，IvorySQL 自动重建视图
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ALTER TABLE t ALTER COLUMN a TYPE bigint;
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-- 验证视图仍然有效，且列类型已更新
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SELECT pg_typeof(a) FROM v LIMIT 1;
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-- 返回 bigint
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pg_typeof
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-----------
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(0 rows)
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\d v
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View "public.v"
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Column | Type | Collation | Nullable | Default
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--------+--------+-----------+----------+---------
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a | bigint | | |
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b | text | | |
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----
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=== 级联视图依赖：按序自动重建
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[source,sql]
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----
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-- 创建基表
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CREATE TABLE t (a int, b text);
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-- 创建两层视图依赖：v2 依赖 v1，v1 依赖 t
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CREATE VIEW v1 AS SELECT a, b FROM t;
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CREATE VIEW v2 AS SELECT a FROM v1;
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-- 修改列类型，自动按依赖顺序重建 v1、v2
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ALTER TABLE t ALTER COLUMN a TYPE bigint;
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-- 验证两个视图均已正确重建
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SELECT pg_typeof(a) FROM v1 LIMIT 1;
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-- 返回 bigint
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pg_typeof
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-----------
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(0 rows)
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SELECT pg_typeof(a) FROM v2 LIMIT 1;
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-- 返回 bigint
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pg_typeof
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-----------
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(0 rows)
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----
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=== 保留视图选项：security_barrier
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[source,sql]
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----
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-- 创建带 security_barrier 选项的视图
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CREATE VIEW v WITH (security_barrier) AS SELECT a, b FROM t;
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ALTER TABLE t ALTER COLUMN a TYPE bigint;
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-- 验证 security_barrier 选项在重建后被正确保留
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SELECT relname, reloptions FROM pg_class WHERE relname = 'v';
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-- reloptions: {security_barrier=true}
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relname | reloptions
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---------+-------------------------
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v | {security_barrier=true}
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(1 row)
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----
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=== 保留视图选项：WITH CHECK OPTION
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[source,sql]
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----
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-- 创建带 WITH LOCAL CHECK OPTION 的视图
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CREATE VIEW v AS SELECT a, b FROM t WHERE a > 0
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WITH LOCAL CHECK OPTION;
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ALTER TABLE t ALTER COLUMN a TYPE bigint;
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-- 验证 CHECK OPTION 在重建后被正确保留
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\d+ v
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View "public.v"
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Column | Type | Collation | Nullable | Default | Storage | Description
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--------+--------+-----------+----------+---------+----------+-------------
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a | bigint | | | | plain |
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b | text | | | | extended |
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View definition:
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SELECT t.a,
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t.b
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FROM t
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WHERE t.a > 0;
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Options: check_option=local
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----
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=== 重建失败时整体回滚
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[source,sql]
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----
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CREATE TABLE t (a int, b text);
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CREATE VIEW v AS SELECT a::integer + 1 AS a_plus FROM t;
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-- 若新类型与视图中的表达式不兼容，整个操作回滚
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-- 例如将 a 改为 text 类型，视图中的 a::integer + 1 将无法执行
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ALTER TABLE t ALTER COLUMN a TYPE text;
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ERROR: operator does not exist: text + integer
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LINE 1: ALTER TABLE t ALTER COLUMN a TYPE text;
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^
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HINT: No operator matches the given name and argument types. You might need to add explicit type casts.
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-- 确认表结构与视图均未受影响
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\d t
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Table "public.t"
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Column | Type | Collation | Nullable | Default
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--------+---------+-----------+----------+---------
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a | integer | | |
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b | text | | |
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----
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== 功能限制
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. 若视图中使用了与新列类型不兼容的操作符或函数（例如对 `text` 类型列执行算术运算），重建将失败，整个 `ALTER TABLE` 操作回滚；
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. 仅支持视图（view）的自动重建，依赖该列的**规则（rule）**仍会报错；
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. 列类型变更需满足 PostgreSQL 类型转换规则，不支持任意两种类型之间的直接转换；
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. 视图重建按依赖拓扑顺序执行，循环依赖（通常由数据库约束避免）不在处理范围内；
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. 重建过程在同一事务内完成，期间依赖视图处于不可用状态，高并发场景下需注意对查询的影响。

‎EN/modules/ROOT/nav.adoc‎

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* IvorySQL Experimental Features
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** xref:v1.17/41.adoc[1、Global Unique Index]
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** xref:v1.17/42.adoc[2、Default Logical Replication Support for Tables Without Primary Key]
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** xref:v1.17/43.adoc[3、Rebuild View After Column Type Changed]
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* xref:v1.17/20.adoc[Community contribution]
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* xref:v1.17/21.adoc[Tool Reference]
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* xref:v1.17/22.adoc[FAQ]
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* xref:v1.17/22.adoc[FAQ]

‎EN/modules/ROOT/pages/v1.17/43.adoc‎

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:sectnums:
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:imagesdir: ./_images
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= Rebuild View After Column Type Changed
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== Feature Overview
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In standard PostgreSQL, if a column is referenced by a view, attempting to change its data type via `ALTER TABLE ... ALTER COLUMN ... TYPE` results
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in an immediate error:
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----
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ERROR: cannot alter type of a column used by a view or rule
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----
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Users are required to manually drop all dependent views, perform the column type change, and then recreate each view one by one — a tedious and
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error-prone process that becomes particularly difficult when multiple levels of cascaded view dependencies exist.
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IvorySQL enhances this behavior: when a column type change is executed, the database automatically saves the definitions of all dependent views
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(including indirectly dependent cascaded views), and after completing the type change, rebuilds those views in the correct dependency order —
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entirely transparent to the user. If an error occurs during rebuilding (for example, a view uses an operator not supported by the new type), the
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entire `ALTER TABLE` operation is rolled back, ensuring data consistency.
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This feature is supported in both PG-compatible mode and Oracle-compatible mode.
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== Syntax
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The syntax is identical to the standard `ALTER TABLE` — no additional keywords are required:
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[source,sql]
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----
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ALTER TABLE table_name ALTER COLUMN column_name TYPE new_type;
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----
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Parameter description:
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- `table_name`: The target table name, optionally schema-qualified;
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- `column_name`: The name of the column whose type is to be changed;
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- `new_type`: The target data type, which must be compatible with the original type or implicitly castable.
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== Test Cases
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=== Single View Dependency: Automatic Rebuild
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[source,sql]
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----
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-- Create the base table
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CREATE TABLE t (a int, b text);
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-- Create a view that references column a
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CREATE VIEW v AS SELECT a, b FROM t;
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-- Standard PostgreSQL would error here; IvorySQL rebuilds the view automatically
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ALTER TABLE t ALTER COLUMN a TYPE bigint;
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-- Verify the view is still valid and the column type has been updated
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SELECT pg_typeof(a) FROM v LIMIT 1;
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-- Returns: bigint
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\d v
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View "public.v"
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Column | Type | Collation | Nullable | Default
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--------+--------+-----------+----------+---------
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a | bigint | | |
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b | text | | |
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----
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=== Cascaded View Dependencies: Ordered Automatic Rebuild
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[source,sql]
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----
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-- Create the base table
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CREATE TABLE t (a int, b text);
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-- Create two levels of view dependency: v2 depends on v1, v1 depends on t
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CREATE VIEW v1 AS SELECT a, b FROM t;
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CREATE VIEW v2 AS SELECT a FROM v1;
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-- Change the column type; v1 and v2 are automatically rebuilt in dependency order
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ALTER TABLE t ALTER COLUMN a TYPE bigint;
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-- Verify both views have been correctly rebuilt
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SELECT pg_typeof(a) FROM v1 LIMIT 1;
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-- Returns: bigint
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pg_typeof
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-----------
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(0 rows)
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SELECT pg_typeof(a) FROM v2 LIMIT 1;
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-- Returns: bigint
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pg_typeof
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-----------
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(0 rows)
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----
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=== Preserving View Options: security_barrier
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[source,sql]
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----
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-- Create a view with the security_barrier option
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CREATE VIEW v WITH (security_barrier) AS SELECT a, b FROM t;
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ALTER TABLE t ALTER COLUMN a TYPE bigint;
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-- Verify the security_barrier option is correctly preserved after rebuild
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SELECT relname, reloptions FROM pg_class WHERE relname = 'v';
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-- reloptions: {security_barrier=true}
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relname | reloptions
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---------+-------------------------
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v | {security_barrier=true}
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(1 row)
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----
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=== Preserving View Options: WITH CHECK OPTION
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[source,sql]
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----
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-- Create a view with WITH LOCAL CHECK OPTION
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CREATE VIEW v AS SELECT a, b FROM t WHERE a > 0
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WITH LOCAL CHECK OPTION;
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ALTER TABLE t ALTER COLUMN a TYPE bigint;
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-- Verify the CHECK OPTION is correctly preserved after rebuild
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\d+ v
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View "public.v"
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Column | Type | Collation | Nullable | Default | Storage | Description
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--------+--------+-----------+----------+---------+----------+-------------
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a | bigint | | | | plain |
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b | text | | | | extended |
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View definition:
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SELECT t.a,
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t.b
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FROM t
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WHERE t.a > 0;
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Options: check_option=local
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----
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=== Full Rollback on Rebuild Failure
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[source,sql]
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----
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CREATE TABLE t (a int, b text);
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CREATE VIEW v AS SELECT a::integer + 1 AS a_plus FROM t;
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-- If the new type is incompatible with expressions in the view, the entire operation rolls back.
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-- For example, changing a to type text makes the expression a::integer + 1 invalid.
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ALTER TABLE t ALTER COLUMN a TYPE text;
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-- ERROR: operator does not exist: text + integer
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-- HINT: ...
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-- ROLLBACK
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-- Confirm that the table structure and view are both unaffected
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\d t
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Table "public.t"
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Column | Type | Collation | Nullable | Default
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--------+---------+-----------+----------+---------
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a | integer | | |
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b | text | | |
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----
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== Limitations
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. If a view uses an operator or function incompatible with the new column type (e.g., arithmetic on a `text` column), the rebuild will fail and the
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entire `ALTER TABLE` operation will be rolled back;
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. Only **views** are automatically rebuilt; **rules** that depend on the affected column will still cause an error;
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. The column type change must satisfy PostgreSQL's type casting rules; arbitrary conversions between unrelated types are not supported;
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. Views are rebuilt in topological dependency order; circular dependencies (normally prevented by the database) are not handled;
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. The rebuild process runs within the same transaction, meaning dependent views are unavailable during the operation — this may affect concurrent
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queries in high-concurrency environments.

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