如果在 Postgresql 中不存在则添加列
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Add Column If Not Exists in Postgresql
提问by postgreat
Is postgresql (9.3.2) can do check the existence of a column before add a new column? I don't want to create a function just for to check the existence.
postgresql ( 9.3.2) 是否可以在添加新列之前检查列是否存在？我不想创建一个函数只是为了检查是否存在。
Just simply like this :
就像这样：
ALTER TABLE IF NOT EXISTS table_name ADD COLUMN column_name data_type;
回答by Thalis K.
You'll need to write your own stored procedure in Plpgsql to check if the table has this column. For this you'll need the tables PG_ATTRIBUTE and PG_CLASS where Postgres stores the schema metadata and in particular the information about columns and tables respectively.
您需要在 Plpgsql 中编写自己的存储过程来检查表是否具有此列。为此，您将需要表 PG_ATTRIBUTE 和 PG_CLASS，其中 Postgres 分别存储架构元数据，特别是有关列和表的信息。
The query whose result you need to check in your stored procedure would be a JOIN like:
您需要在存储过程中检查其结果的查询将是一个 JOIN，如：
SELECT A.ATTNAME FROM PG_ATTRIBUTE A, PG_CLASS C
WHERE A.ATTRELID = C.OID AND A.ATTNAME = 'column_name_check_if_exists' AND C.relname= 'table_name' ;
回答by jokie1982
In DDL, you can only:
在 DDL 中，您只能：
- Add columns
- Remove columns
- Add constraints
- Remove constraints
- Change default values
- Change column data types
- Rename columns
- Rename tables
- 添加列
- 删除列
- 添加约束
- 移除约束
- 更改默认值
- 更改列数据类型
- 重命名列
- 重命名表
ALTER TABLE: SYNOPSIS AND EXAMPLES -> http://www.postgresql.org/docs/9.3/static/sql-altertable.html
更改表：概要和示例 -> http://www.postgresql.org/docs/9.3/static/sql-altertable.html
For validations... you need make "PL/SQL"
对于验证......你需要制作“PL/SQL”
回答by postgreat
So, there is no such query. I should using PLPGSQL.
所以，没有这样的查询。我应该使用 PLPGSQL。
