Is there a difference between
1st Way
Alter Table Test_Table
Add Test_Column
and
2nd way
Alter Table Test_Table
Add Column Test_Column
Alter Table Test_Table Add Test_Column
Use for Add new columns in table
Alter Table Test_Table Add Column Test_Column
use for Modify column in table
It depends on the database.
For example Oracle enough
ALTER TABLE xxx ADD column_name TYPE;
But in postgresql you must column after add
ALTER TABLE xxx ADD COLUMN column_name TYPE;
I'm using firebird and attempting to drop a column but the following SQL does not work:
ALTER TABLE student DROP COLUMN id;
You must omit the "COLUMN" keyword:
ALTER TABLE student DROP id;
Try this
ALTER TABLE Table_name DROP columnname;
refer this link
How can I accomplish this using Postgres? I've tried the code below but it doesn't work:
ALTER TABLE mytable ALTER COLUMN mycolumn BIGINT NULL;
From the fine manual:
ALTER TABLE mytable ALTER COLUMN mycolumn DROP NOT NULL;
There's no need to specify the type when you're just changing the nullability.
What is the SQL to make a field go from nvarchar(50) to nvarchar(250)?
When I try to change it through the SQL Server Management Studio, it doesn't allow me to do it, so I figured I would try SQL directly instead of using the GUI.
Alter table tblname ALTER Column colname nvarchar(250) [NOT] NULL
If NULL / NOT NULL is not specified the column will become Nullable irrespective of what ever the original specification was.
ALTER TABLE MyTable
ALTER COLUMN MyColumn varchar(NewSize)
The ALTER TABLE Statement
The ALTER TABLE statement is used to add, delete, or modify columns in an existing table.
SQL ALTER TABLE Syntax
To add a column in a table, use the following syntax:
ALTER TABLE table_name
ADD column_name datatype
To delete a column in a table, use the following syntax (notice that some database systems don't allow deleting a column):
ALTER TABLE table_name
DROP COLUMN column_name
To change the data type of a column in a table, use the following syntax:
SQL Server / MS Access:
ALTER TABLE table_name
ALTER COLUMN column_name datatype
My SQL / Oracle (prior version 10G):
ALTER TABLE table_name
MODIFY COLUMN column_name datatype
Oracle 10G and later:
ALTER TABLE table_name
MODIFY column_name datatype
Its sometimes safer to check if the table exist in the first place...
IF COL_LENGTH('[tablename]','[tablecolumn]') IS NULL
BEGIN
ALTER TABLE tablename
ALTER COLUMN [tablecolumn]
NVARCHAR(500)
END
To change the datatype of many column but same datatype
alter table employee modify (firstname varchar2(9),lastname varchar2(9),email varchar2(9));
-- Table altered.
alter table employee modify (firstname,lastname,email varchar2(9));
-- Table altered.
For Oracle SQL Developers
Alter table tblname MODIFY (colname varchar2(250));
Description : It will increase the length of column. where 250
represent the updated (incremented) length of column.
I want to alter a table column to be nullable. I have used:
ALTER TABLE Merchant_Pending_Functions Modify NumberOfLocations NULL
This gives an error at Modify. What is the correct syntax?
Assuming SQL Server (based on your previous questions):
ALTER TABLE Merchant_Pending_Functions ALTER COLUMN NumberOfLocations INT NULL
Replace INT with your actual datatype.
If this was MySQL syntax, the type would have been missing, as some other responses point out.
Correct MySQL syntax would have been:
ALTER TABLE Merchant_Pending_Functions MODIFY NumberOfLocations INT NULL
Posting here for clarity to MySQL users.
In PostgresQL it is:
ALTER TABLE tableName ALTER COLUMN columnName DROP NOT NULL;
for Oracle Database 10g users:
alter table mytable modify(mycolumn null);
You get "ORA-01735: invalid ALTER TABLE option" when you try otherwise
ALTER TABLE mytable ALTER COLUMN mycolumn DROP NOT NULL;
Although I don't know what RDBMS you are using, you probably need to give the whole column specification, not just say that you now want it to be nullable. For example, if it's currently INT NOT NULL, you should issue ALTER TABLE Merchant_Pending_Functions Modify NumberOfLocations INT.
As others have observed, the precise syntax for the command varies across different flavours of DBMS. The syntax you use works in Oracle:
SQL> desc MACAddresses
Name Null? Type
----------------------------------------- -------- ----------------------------
COMPUTER NUMBER
MACADDRESS VARCHAR2(12)
CORRECTED_MACADDRESS NOT NULL VARCHAR2(17)
SQL> alter table MACAddresses
2 modify corrected_MACAddress null
3 /
Table altered.
SQL> desc MACAddresses
Name Null? Type
----------------------------------------- -------- ----------------------------
COMPUTER NUMBER
MACADDRESS VARCHAR2(12)
CORRECTED_MACADDRESS VARCHAR2(17)
SQL>
For SQL Server or TSQL
ALTER TABLE Complaint.HelplineReturn ALTER COLUMN IsDisposed BIT NULL
This depends on what SQL Engine you are using, in Sybase your command works fine:
ALTER TABLE Merchant_Pending_Functions
Modify NumberOfLocations NULL;
For HSQLDB:
ALTER TABLE tableName ALTER COLUMN columnName SET NULL;
ALTER TABLE Merchant_Pending_Functions MODIFY COLUMN `NumberOfLocations` INT null;
This will work for you.
If you want to change a not null column to allow null, no need to include not null clause. Because default columns get not null.
ALTER TABLE Merchant_Pending_Functions MODIFY COLUMN `NumberOfLocations` INT;
Oracle
ALTER TABLE Merchant_Pending_Functions MODIFY([column] NOT NULL);
SQLite
The ALTER TABLE command is a bit special. There is no possibility to modify a column. You have to create a new column, migrate the data, and then drop the column:
-- 1. First rename
ALTER TABLE
Merchant_Pending_Functions
RENAME COLUMN
NumberOfLocations
TO
NumberOfLocations_old
-- 2. Create new column
ALTER TABLE
Merchant_Pending_Functions
ADD COLUMN
NumberOfLocations INT NULL
-- 3. Migrate data - you need to write code for that
-- 4. Drop the old column
ALTER TABLE
Merchant_Pending_Functions
DROP COLUMN
NumberOfLocations_old
Make sure you add the data_type of the column to modify.
ALTER TABLE TABLE_NAME MODIFY COLUMN_NAME DATA_TYPE NULL;