{"id":23628,"date":"2018-08-13T06:29:06","date_gmt":"2018-08-13T06:29:06","guid":{"rendered":"https:\/\/data-flair.training\/blogs\/?p=23628"},"modified":"2021-03-10T21:53:25","modified_gmt":"2021-03-10T16:23:25","slug":"alter-command-in-sql-truncate","status":"publish","type":"post","link":"https:\/\/data-flair.training\/blogs\/alter-command-in-sql-truncate\/","title":{"rendered":"Alter Command In SQL | Truncate Table In SQL"},"content":{"rendered":"

SQL provides us with the flexibility to modify and delete a table after it\u2019s creation. We have data that needs to be put in the table and, at the same time, data that is of no use after a particular time.<\/p>\n

To keep our data updated, we need to take various measures, and table altering is one of those. Alter and Drop commands are applicable for the same.<\/p>\n

Demo Database<\/h3>\n

Let us view the database that we will use here, using the SELECT query.
\nSyntax:\u00a0<\/strong><\/p>\n

SELECT * FROM tableName ;<\/pre>\n
Query:\u00a0<\/strong><\/p>\n
Select * from dataflair_employee ;\r\n<\/pre>\n
\"SQL<\/a><\/p>\n
We have 5 columns, namely:<\/strong><\/p>\n
    \n
  1. name_emp<\/li>\n
  2. post_emp<\/li>\n
  3. email<\/li>\n
  4. age<\/li>\n
  5. salary<\/li>\n<\/ol>\n
    What is an Alter Command in SQL?<\/h3>\n
    Alter command is applicable to add, modify, or update columns in an existing table. It is also applicable to drop or delete a table. The basic syntax of the alter command is as follows:<\/p>\n
    Syntax:<\/strong><\/p>\n
    ALTER TABLE tableName\r\noperation columnName datatype;\r\n<\/pre>\n
    We can perform the following tasks using the Alter Command:<\/strong><\/p>\n
    1. ADD Column in SQL<\/h4>\n
    Used to add a new column to the existing table.
    \nSyntax:<\/strong><\/p>\n
    ALTER TABLE tableName\r\nADD columnName datatype ;\r\n<\/pre>\n
    Example 1:<\/strong> Let us add a gender column in the table.
    \nQuery:<\/strong><\/p>\n
    ALTER TABLE dataflair_employee\r\nADD gender varchar(10);\r\n<\/pre>\n
    \"rename<\/a><\/p>\n
    2. MODIFY Column in SQL<\/h4>\n
    Used to modify the already existing columns in a database. We can modify one or multiple columns at once.<\/p>\n
    Syntax:<\/strong><\/p>\n
    ALTER TABLE tableName\r\nMODIFY columnName columnType;\r\n<\/pre>\n
    Example 1:<\/strong> Let us modify the size of our name column to 100 in varchar.
    \nQuery:<\/strong><\/p>\n
    ALTER TABLE dataflair_employee\r\nMODIFY name_emp varchar(100);\r\n<\/pre>\n
    \"modify<\/a><\/p>\n
    We can see the name_emp column has changed in size from varchar(50) to varchar(100).<\/p>\n
    3. RENAME Column in SQL<\/h4>\n
    Rename is put with Alter to change the name of a column. This could be applicable due to various reasons, for example:<\/p>\n