Difference between ALTER and UPDATE Command in SQL

1. ALTER Command:

ALTER SQL command is a DDL (Data Definition Language) statement. ALTER is used to update the structure of the table in the database (like add, delete, modify the attributes of the tables in the database).

Syntax:

// add a column to the existing table

ALTER TABLE tableName

ADD columnName columnDefinition;

 

// drop a column from the existing table

ALTER TABLE tableName

DROP COLUMN columnName;



// rename a column in the existing table

ALTER TABLE tableName

RENAME COLUMN olderName TO newName;



// modify the datatype of an already existing column in the table

ALTER TABLE table_name

ALTER COLUMN column_name column_type;

2. UPDATE Command:

UPDATE SQL command is a DML (Data manipulation Language) statement. It is used to manipulate the data of any existing column. But can’t be change the table’s definition.

Syntax:

// table name that has to update

UPDATE tableName

// which columns have to update

SET column1 = value1, column2 = value2, ...,columnN=valueN.

// which row you have to update

WHERE condition

Note :  Without WHERE clause, all records in the table will be updated.

Difference Between ALTER and UPDATE Command in SQL: 

The Alter statement is is used when we needs to change something in table or modify the table whereas the Update statement is used when user wants to modify something in data which is stored in the table. We can say that Alter works with table structure of the table and Update works with data within the table.