i want to add a new column noOfTry in a table which already have some columns. the column data will be integer type and default value will be 0. i know i need to use alter query, just asking for the correct format of the query for this case
The simplest option would be
ALTER TABLE MyTable ADD COLUMN noOfTry INT NOT NULL DEFAULT 0;
alter table `database`.`table`
add column `noOfTry` int(11) DEFAULT '0' NULL after `column`;
where column is the column before the on you want to add if you want to add in the middle of the table but this is optional.
Related
Hello I need to edit a database to add new columns. But I encountered a little problem, because I need to add comments to these new columns and I also need to add them after a certain column in the exist table.
Is this the correct syntax? :
ALTER TABLE `table`
ADD COLUMN `new` VARCHAR(50) NOT NULL DEFAULT '' COMMENT '...' AFTER `secondlastcolumn`;
Or would this be correct? :
ALTER TABLE `table`
ADD COLUMN `new` VARCHAR(50) NOT NULL DEFAULT '' AFTER `secondlastcolumn` COMMENT '...';
Or is there another way of doing this?
I couldn't find a answer with an ADD COLUMN, only for modifying columns.
ALTER TABLE Statement defines ADD COLUMN definition as
ADD [COLUMN] col_name column_definition [FIRST | AFTER col_name]
CREATE TABLE Statement defines COMMENT is a part of column_definition.
So COMMENT then AFTER.
How to add the column using alter by inputting the values on it?
As the example, I want to add tempID's column which has value "3" on every row
Maybe it's something like this
ALTER TABLE NAMEYOURTABLE
ADD COLUMN last_update TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
but the code above is only for the timestamp, not for integer values. Thanks in advance
You should check out this https://dev.mysql.com/doc/refman/5.7/en/alter-table.html
For your case it would be something like
ALTER TABLE NAMEYOURTABLE ADD COLUMN tempID int NULL DEFAULT 3;
Along with Jovana's answer, you can specify after which column you need the new column with AFTER .
ALTER TABLE NAMEYOURTABLE ADD tempID int NULL DEFAULT 3
AFTER YOUREXISTINGCOLUMNNAME;
Refer : https://www.w3schools.com/sql/sql_alter.asp
Example to add a column:
ALTER TABLE table_name
ADD column_name datatype;
Is it possible to set a default value for new records only in a mysql column?
I want all rows before today to be null if nothing has been entered, but any new rows added after today to be a specific string if nothing has be entered for that column.
Is this possible?
Search in all rows in the table and check if the specific column is empty, if yes set it to null.
UPDATE tablename SET column = CASE column WHEN '' THEN NULL ELSE column END
For future entries you can add to your table a Default Constraint like this:
ALTER TABLE tablename ALTER column SET DEFAULT 'specific string'
This is an old post but I do think this answer might help other folks.
ALTER TABLE object_table_name ADD `value` INT NULL;
ALTER TABLE object_table_name MODIFY COLUMN `value` INT DEFAULT 0;
Doing it this way will only impact newly inserted records, this code did not work for me
ALTER TABLE object_table_name ADD `value` INT DEFAULT 0
I'm using MySQL 5.6
I am having a table in sql with 20 rows inserted.In future it may need to add a another column.
In case of adding column values for the particular column will starts from the 21 line,previous rows values in particular column will be null.
I don't want to have null values on those rows.How can i alter the table for that.
You need to do two steps
1 Alter the table
Alter table table_name add column new_col datatype
2 Update that column into some default value
Update table_name set new_col='some value'
Do it in this way:
alter table tbl_sample add COLUMN sampleadd_column VARCHAR(50) default 'just a sample';
this should work for you;
I know, we cannot rename a column using MODIFY COLUMN syntax, but we can using CHANGE COLUMN syntax.
My question is: what is the main usage of modify syntax?
For example:
ALATER TABLE tablename CHANGE col1 col1 INT(10) NOT NULL;
instead of
ALATER TABLE tablename MODIFY col1 INT(10) NOT NULL;
Edited (question replaced)
What is the main usage of MODIFY syntax?
Why we have to use CHANGE COLUMN instead of MODIFYCOLUMN?
CHANGE COLUMN
If you have already created your MySQL database, and decide after the fact that one of your columns is named incorrectly, you don't need to remove it and make a replacement, you can simply rename it using change column.
ALTER TABLE MyTable CHANGE COLUMN foo bar VARCHAR(32) NOT NULL FIRST;
MODIFY COLUMN
This command does everything CHANGE COLUMN can, but without renaming the column. You can use the MODIFY SQL command if you need to resize a column in MySQL. By doing this you can allow more or less characters than before. You can't rename a column using MODIFY and other.
ALTER TABLE MyTable MODIFY COLUMN foo VARCHAR(32) NOT NULL AFTER baz;
Note
ALTER TABLE is used for altering a table in order to change column name, size, drop column etc. CHANGE COLUMN and MODIFY COLUMN commands cannot be used without help of ALTER TABLE command.
The difference is whether you want to change the column name, column definition or both.
CHANGE
Can change a column name or definition, or both
ALTER TABLE t1 CHANGE a b BIGINT NOT NULL
MODIFY
Can change a column definition but not its name
ALTER TABLE t1 MODIFY b INT NOT NULL
RENAME COLUMN (from MySQL 8.0)
Can change a column name but not its definition
ALTER TABLE t1 RENAME COLUMN b TO a
Also, CHANGE and MODIFY can be followed by an optional COLUMN keyword.
For complete explanation:
MySQL 5.7 Docs- Renaming, Redefining, and Reordering Columns
MySQL 8.0 Docs- Renaming, Redefining, and Reordering Columns
I found one difference after more than an hour of effort in trying to make a non auto_increment column into auto_increment
statement:
alter table `doctor_experience` modify column `id` int(11) unsigned auto_increment
works, but statment:
alter table `doctor_experience` change column `id` `id` int(11) unsigned auto_increment
will report an error.
That is the same. It was done to support another syntax (Oracle ALTER TABLE as I know). You can use both of them.
Note: ALTER TABLE CHANGE old_col_name new_col_name syntax allows renaming column using one command.
Change Column : Used when we want to change the column name with its definition.
eg - alter table student CHANGE name full_name VARCHAR(32) NOT NULL;
Modify column : Used when column name is to be same but change in its definition.
eg - alter table student MODIFY full_name VARCHAR(64) NOT NULL;
Rename column : Used when we only need to change the column name (its definition will be same)
alter table student RENAME COLUMN full_name TO name;