Learn Database Concepts

Create table sql :  CREATE TABLE ABC (  ID NUMBER , NAME VARCHAR2(20 BYTE) ) ; Lets insert duplicate values into it: INSERT INTO ABC (ID, NAME) VALUES ('15', 'f'); INSERT INTO ABC (ID, NAME) VALUES ('15', 'f'); INSERT INTO ABC (ID, NAME) VALUES ('15', 'f'); INSERT INTO ABC (ID, NAME) VALUES ('11', 'B'); INSERT INTO ABC (ID, NAME) VALUES ('11', 'B'); INSERT INTO ABC (ID, NAME) VALUES ('13', 'G'); INSERT INTO ABC (ID, NAME) VALUES ('13', 'G'); Now table looks like this:                     Now we have a duplicate combination of 2 columns. sql to find duplicate values combination in two columns:    select ID,NAME, count(ID) from ABC group by ID,NAME having count(ID) > 1; sample output:   Find the duplicate ID's in a column :  select ID, count(ID) from ABC group by ID having count(ID) > 1; Sample output:  Retrieving duplicate values

Grant select  permission on all tables in logged in schema to a user/role: declare cursor c1 is select table_name from user_tables; cmd varchar2(200); begin for c in c1 loop cmd := 'GRANT SELECT ON '||c.table_name||' TO &&YOURUSERNAME'; execute immediate cmd; end loop; end; Note : you change the select to what ever permissions you want to grant. This will be very helpful in case of huge number of tables.

lets take a simple example here. create a table and leave id column empty and add values to other column name. Sample create table : create table abc ( id number, name varchar2(20)); add values to name column and leave the id column empty INSERT INTO ABC (NAME) VALUES ('a'); INSERT INTO ABC (NAME) VALUES ('b'); INSERT INTO ABC (NAME) VALUES ('c'); INSERT INTO ABC (NAME) VALUES ('d'); INSERT INTO ABC (NAME) VALUES ('e'); INSERT INTO ABC (NAME) VALUES ('f'); INSERT INTO ABC (NAME) VALUES ('g'); INSERT INTO ABC (NAME) VALUES ('h'); Now we have a situation where we have a table with only values in the name column and id column is empty (in case if u want to add id's to already existing table  just add a column for the new unique ID's ).  Now we will create a sequence to get the sequential values to update with. create a sequence : CREATE SEQUENCE SEQ_abc START WITH 1 MAXVALUE 99999 MINVALUE 1 NOCYCLE NOCACHE NOORDER;