在将列添加到PL/SQL中的现有表之前，如何检查该列是否存在? [英] How to check if a column exists before adding it to an existing table in PL/SQL?

问题描述

在将列添加到oracle数据库的表之前，如何添加简单的检查?我已经包含了用于添加列的SQL.

How do I add a simple check before adding a column to a table for an oracle db? I've included the SQL that I'm using to add the column.

ALTER TABLE db.tablename 
  ADD columnname NVARCHAR2(30);

推荐答案

可使用以下视图之一访问有关Oracle数据库中列的所有元数据.

All the metadata about the columns in Oracle Database is accessible using one of the following views.

user_tab_cols ； -对于用户拥有的所有表

user_tab_cols; -- For all tables owned by the user

all_tab_cols ； -对于用户可访问的所有表

all_tab_cols ; -- For all tables accessible to the user

dba_tab_cols ； -适用于数据库中的所有表.

dba_tab_cols; -- For all tables in the Database.

因此，如果要在SCOTT.EMP表中查找类似ADD_TMS的列，并仅在不存在该列时添加该列，则PL/SQL代码将遵循以下内容.

So, if you are looking for a column like ADD_TMS in SCOTT.EMP Table and add the column only if it does not exist, the PL/SQL Code would be along these lines..

DECLARE
  v_column_exists number := 0;  
BEGIN
  Select count(*) into v_column_exists
    from user_tab_cols
    where upper(column_name) = 'ADD_TMS'
      and upper(table_name) = 'EMP';
      --and owner = 'SCOTT --*might be required if you are using all/dba views

  if (v_column_exists = 0) then
      execute immediate 'alter table emp add (ADD_TMS date)';
  end if;
end;
/

如果您打算将其作为脚本(而不是过程的一部分)运行，则最简单的方法是在脚本中包含alter命令，并在脚本末尾看到错误(假设您没有Begin). -结束脚本.

If you are planning to run this as a script (not part of a procedure), the easiest way would be to include the alter command in the script and see the errors at the end of the script, assuming you have no Begin-End for the script..

如果您有file1.sql

If you have file1.sql

alter table t1 add col1 date;
alter table t1 add col2 date;
alter table t1 add col3 date;

并且存在col2，在运行脚本时，会将其他两列添加到表中，并且日志将显示错误消息"col2"已经存在，因此您应该没事.

And col2 is present,when the script is run, the other two columns would be added to the table and the log would show the error saying "col2" already exists, so you should be ok.

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