How to check if a column exists before adding it to an existing table in PL/SQL?
All the metadata about the columns in Oracle Database is accessible using one of the following views.
user_tab_cols; -- For all tables owned by the user
all_tab_cols ; -- For all tables accessible to the user
dba_tab_cols; -- For all tables in the Database.
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;/
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..
If you have file1.sql
alter table t1 add col1 date;alter table t1 add col2 date;alter table t1 add col3 date;
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.
Normally, I'd suggest trying the ANSI-92 standard meta tables for something like this but I see now that Oracle doesn't support it.
-- this works against most any other databaseSELECT * FROM INFORMATION_SCHEMA.COLUMNS C INNER JOIN INFORMATION_SCHEMA.TABLES T ON T.TABLE_NAME = C.TABLE_NAME WHERE C.COLUMN_NAME = 'columnname' AND T.TABLE_NAME = 'tablename'
Instead, it looks like you need to do something like
-- Oracle specific table/column querySELECT * FROM ALL_TAB_COLUMNS WHERE TABLE_NAME = 'tablename' AND COLUMN_NAME = 'columnname'
I do apologize in that I don't have an Oracle instance to verify the above. If it does not work, please let me know and I will delete this post.