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;
Related
How do I remove AUTO_INCREMENT of a column in DB2?
I tried
ALTER TABLE my_table ALTER my_id
but no luck. What is the correct SQL statement?
You can modify a column definition of a DB2 table and remove the generation of values:
ALTER TABLE mytable ALTER COLUMN mycol DROP GENERATED;
You can remove the Auto_increment by using the following
ALTER TABLE table_name ALTER COLUMN column_name DROP IDENTITY;
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
I have a table (that contains data) in Oracle 11g and I need to use Oracle SQLPlus to do the following:
Target: change the type of column TEST1 in table UDA1 from number to varchar2.
Proposed method:
backup table
set column to null
change data type
restore values
The following didn't work.
create table temp_uda1 AS (select * from UDA1);
update UDA1 set TEST1 = null;
commit;
alter table UDA1 modify TEST1 varchar2(3);
insert into UDA1(TEST1)
select cast(TEST1 as varchar2(3)) from temp_uda1;
commit;
There is something to do with indexes (to preserve the order), right?
create table temp_uda1 (test1 integer);
insert into temp_uda1 values (1);
alter table temp_uda1 add (test1_new varchar2(3));
update temp_uda1
set test1_new = to_char(test1);
alter table temp_uda1 drop column test1 cascade constraints;
alter table temp_uda1 rename column test1_new to test1;
If there was an index on the column you need to re-create it.
Note that the update will fail if you have numbers in the old column that are greater than 999. If you do, you need to adjust the maximum value for the varchar column
Add new column as varchar2, copy data to this column, delete old column, rename new column as actual column name:
ALTER TABLE UDA1
ADD (TEST1_temp VARCHAR2(16));
update UDA1 set TEST1_temp = TEST1;
ALTER TABLE UDA1 DROP COLUMN TEST1;
ALTER TABLE UDA1
RENAME COLUMN TEST1_temp TO TEST1;
Look at Oracle's package DBMS_REDEFINE. With some luck you can do it online without downtime - if needed. Otherwise you can:
Add new VARCHAR2 column
Use update to copy NUMBER into VARCHAR2
Drop NUMBER column
Rename VARCHAR2 column
Here you go, this solution did not impact the existing NOT NULL or Primary key constraints. Here i am going to change the type of Primary key from Number to VARCHAR2(3), Here are the Steps on example table employee.
Take backup of table and Index, Constraints
created table employee_bkp
create table employee_bkp as select * from employee
commit;
Truncate the table to empty it
truncate table employee
Alter the table to change the type
ALTER TABLE employee MODIFY employee_id varchar2(30);
Copy the data back from backup table
insert into employee (select * from employee_bkp)
commit;
Verify
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;