Alter table command
- 1. ALTER TABLE COMMAND This is a part of DDL command . The ALTER table command is used to change definition of existing table usually it can add columns to a table. It can delete column and change their sizes. In MY SQL alter table command is used… 1. To Add a New Column 2. To Add an Integrity Constraints 3. To Redefine a column (Data type, size, default value) 1. Adding Column:- We can add a new column in existing table with the help of ALTER table command. To ADD a new column use ADD command with the ALTER table command. The new column will be added with NULL values for all rows currently in the table. Syntax :- ALTER TABLE tablename ADD(newcolumname datatype(size)); Example :- ALTER TABLE STUDENT ADD(CITY VARCHAR(20));
- 2. Q1. To Insert a Record in new column. UPDATE STUDENT SET CITY=’ALWAR’; Insert into student values(‘alwar’);--- wrong query Modify command:- We can use the MODIFY command with alter table command to change structure of table. We can change following parts of a table:- Data Type Size Default Value Order of Column 1) Data Type and Size Syntax ;- Alter Table tablename Modify columnname newdatatype(new size); Example:- Alter table student Modify phoneno varchar(20);
- 3. Alter table student Modify city default ‘jaipur’;