What command do we write to drop a column from a table?

Note: Be careful when deleting records in a table! Notice the WHERE clause in the DELETE statement. The WHERE clause specifies which record(s) should be deleted. If you omit the WHERE clause, all records in the table will be deleted! Demo Database Below is a selection from the "Customers" table in the Northwind sample database: CustomerID CustomerName ContactName Address City PostalCode Country 1 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany 2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico 3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico 4 Around the Horn Thomas Hardy 120 Hanover Sq. London WA1 1DP UK 5 Berglunds snabbköp Christina Berglund Berguvsvägen 8 Luleå S-958 22 Sweden CustomerID CustomerName ContactName Address City PostalCode Country 2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico 3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico 4 Around the Horn Thomas Hardy 120 Hanover Sq. London WA1 1DP UK 5 Berglunds snabbköp Christina Berglund Berguvsvägen 8 Luleå S-958 22 Sweden Delete All Records It is possible to delete all rows in a table without deleting the table. This means that the table structure, attributes, and indexes will be intact:

alter command is used for altering the table structure, such as, • to add a column to existing table • to rename any existing column • to change datatype of any column or to modify its size. • to drop a column from the table. ALTER Command: Add a new Column Using ALTER command we can add a column to any existing table. Following is the syntax, ALTER TABLE table_name ADD( column_name datatype); Here is an Example for this, ALTER TABLE student ADD( address VARCHAR(200) ); The above command will add a new column address to the table student, which will hold data of type varchar which is nothing but string, of length 200. ALTER Command: Add multiple new Columns Using ALTER command we can even add multiple new columns to any existing table. Following is the syntax, ALTER TABLE table_name ADD( column_name1 datatype1, column-name2 datatype2, column-name3 datatype3); Here is an Example for this, ALTER TABLE student ADD( father_name VARCHAR(60), mother_name VARCHAR(60), dob DATE); The above command will add three new columns to the student table ALTER Command: Add Column with default value ALTER command can add a new column to an existing table with a default value too. The default value is used when no value is inserted in the column. Following is the syntax, ALTER TABLE table_name ADD( column-name1 datatype1 DEFAULT some_value ); Here is an Example for this, ALTER TABLE student ADD( dob DATE DEFAULT '01-Jan-99' ); The above command will add a new column with a preset default valu...

Summary: in this tutorial, you will learn how to use the SQL Server ALTER TABLE DROP column statement to remove one or more columns from existing table. Introduction to SQL Server ALTER TABLE DROP COLUMN Sometimes, you need to remove one or more unused or obsolete columns from a table. To do this, you use the ALTER TABLE DROP COLUMN statement as follows: ALTER TABLE table_name DROP COLUMN column_name; Code language: SQL (Structured Query Language) ( sql ) In this syntax: • First, specify the name of the table from which you want to delete the column. • Second, specify the name of the column that you want to delete. If the column that you want to delete has a If you want to delete multiple columns at once, you use the following syntax: ALTER TABLE table_name DROP COLUMN column_name_1, column_name_2,...; Code language: SQL (Structured Query Language) ( sql ) In this syntax, you specify columns that you want to drop as a list of comma-separated columns in the DROP COLUMN clause. SQL Server ALTER TABLE DROP COLUMN examples Let’s sales.price_lists for the demonstration. CREATE TABLE sales.price_lists( product_id int, valid_from DATE, price DEC( 10, 2) NOT NULL CONSTRAINT ck_positive_price CHECK(price >= 0), discount DEC( 10, 2) NOT NULL, surcharge DEC( 10, 2) NOT NULL, note VARCHAR( 255), PRIMARY KEY(product_id, valid_from) ); Code language: SQL (Structured Query Language) ( sql ) The following statement drops the note column from the price_lists table: ALTER TABLE sales.price_...

Caution When you delete a column from a table, the column and all the data it contains are deleted. Limitations and restrictions You can't delete a column that has a CHECK constraint. You must first delete the constraint. You can't delete a column that has PRIMARY KEY or FOREIGN KEY constraints or other dependencies except when using the Permissions Requires ALTER permission on the table. Delete columns using Object Explorer The following steps explain how to delete columns with Object Explorer in SSMS: • In Object Explorer, connect to an instance of Database Engine. • In Object Explorer, locate the table from which you want to delete columns, and expand to expose the column names. • Right-click the column that you want to delete, and choose Delete. • In Delete Object dialog box, click OK. If the column contains constraints or other dependencies, an error message will display in the Delete Object dialog box. Resolve the error by deleting the referenced constraints. Delete columns using Table Designer The following steps explain how to delete columns with Table Designer in SSMS: • In Object Explorer, right-click the table from which you want to delete columns and choose Design. • Right-click the column you want to delete and choose Delete Column from the shortcut menu. • If the column participates in a relationship (FOREIGN KEY or PRIMARY KEY), a message prompts you to confirm the deletion of the selected columns and their relationships. Choose Yes. Delete columns using Tra...

I would like to write a single SQL command to drop multiple columns from a single table in one ALTER TABLE statement. From DROP Specifies that constraint_name or column_name is removed from the table. DROP COLUMN is not allowed if the compatibility level is 65 or earlier. Multiple columns and constraints can be listed. It says that mutliple columns can be listed in the the statement but the syntax doesn't show an optional comma or anything that would even hint at the syntax. How should I write my SQL to drop multiple columns in one statement (if possible)? For SQL Server: ALTER TABLE TableName DROP COLUMN Column1, Column2; The syntax is DROP [ ,...n ] For MySQL: ALTER TABLE TableName DROP COLUMN Column1, DROP COLUMN Column2; or like this 1: ALTER TABLE TableName DROP Column1, DROP Column2; 1 The word COLUMN is optional and can be omitted, except for RENAME COLUMN (to distinguish a column-renaming operation from the RENAME table-renaming operation). More info Summarizing ALTER TABLE table_name DROP (column_name1, column_name2); ALTER TABLE table_name DROP COLUMN column_name1, column_name2 ALTER TABLE table_name DROP column_name1, DROP column_name2; ALTER TABLE table_name DROP COLUMN column_name1, DROP COLUMN column_name2; Be aware DROP COLUMN does not physically remove the data for some DBMS. E.g. for MS SQL. For fixed length types ( int, numeric, float, datetime, uniqueidentifier etc) the space is consumed even for records added after the columns were dropped. To get rid...

In SQL, you can delete a row in a table by using the DELETE query and the WHERE clause. In the article, I will walk you through how to use the DELETE query and WHERE clause to delete rows. I will also show you how to delete multiple rows from a table at once. How to use the DELETE query in SQL This is the basic syntax for using the the DELETE query: DELETE FROM table_name WHERE condition of which row(s) to delete; In this example, we have a table called cats that currently has ten rows in it. The columns would be id, name and gender. We want to delete the row with the id of 8 which is Loki's row. The first line of the DELETE query would look like this: DELETE FROM cats In the second line, we are going to specify which row by using the id=8 after the WHERE clause. WHERE id=8; Here is the complete syntax to delete Loki's row: DELETE FROM cats WHERE id=8; This is what the new cats table looks like: We can see that our DELETE query worked because Loki's information is no longer there. How to Delete multiple rows from a table in SQL One way we can delete multiple rows from our cats table is to change the condition from id to gender. If we wanted to delete the rows with just the male cats, then we can use the gender="M" condition. DELETE FROM cats WHERE gender="M"; Our new cats table would look like this: Now the cats table is only showing the female cats. How to delete multiple rows using the BETWEEN operator with the AND operator in SQL If we wanted to delete a number of rows ...