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Give initial auto increment value while table creation

February 2, 2023February 2, 2023 by manish

When we create a table we can give a auto increment value to a primary key filed. This field is auto incremented by one for newly inserted value. To start auto increment from specified number AUTO_INCREMENT = value is used while creating table. Example:

CREATE TABLE students (
   id int(5) not null AUTO_INCREMENT, 
   firstname varchar(30),
   lastname varchar(30),
   class varchar(30),
    PRIMARY KEY (id)
) AUTO_INCREMENT = 1001;

CREATE TABLE students (

id int(5) not null AUTO_INCREMENT,

firstname varchar(30),

lastname varchar(30),

class varchar(30),

PRIMARY KEY (id)

) AUTO_INCREMENT = 1001;

If you have already created a table and then want … Read more

Finding all column name of table

February 2, 2023 by manish

Suppose we have a table user and we want to fetch all its column name.For this we use INFORMATION_SCHEMA. we will use following query to fetch all column name of table

SELECT `COLUMN_NAME` 
FROM `INFORMATION_SCHEMA`.`COLUMNS` 
WHERE `TABLE_SCHEMA`='social' 
    AND `TABLE_NAME`='user';

SELECT `COLUMN_NAME`

FROM `INFORMATION_SCHEMA`.`COLUMNS`

WHERE `TABLE_SCHEMA`='social'

AND `TABLE_NAME`='user';

Above query will fetch all columns of user table available in social database. Read More Setting innodb_lock_wait_timeout Set time zone in mysql … Read more

Drop command to remove a column from a table.

February 2, 2023February 2, 2023 by bharti

suppose we have a column address in table employee.

create table employee( id int(10) NOT NULL AUTO_INCREMENT,
       name varchar(40),
       department varchar(30),
       address varchar(50),
       PRIMARY KEY(id));

create table employee( id int(10) NOT NULL AUTO_INCREMENT,

name varchar(40),

department varchar(30),

address varchar(50),

PRIMARY KEY(id));

To see the description of table we use desc employee that will produce following result here we can see the description of table.

mysql&gt; desc employee;
+------------+-------------+------+-----+---------+----------------+
| Field      | Type        | Null | Key | Default | Extra          |
+------------+-------------+------+-----+---------+----------------+
| id         | int(10)     | NO   | PRI | NULL    | auto_increment |
| name       | varchar(40) | YES  |     | NULL    |                |
| department | varchar(30) | YES  |     | NULL    |                |
| address    | varchar(50) | YES  |     | NULL    |                |
+------------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

mysql> desc employee;

+------------+-------------+------+-----+---------+----------------+

+------------+-------------+------+-----+---------+----------------+

| id | int(10) | NO | PRI | NULL | auto_increment |

+------------+-------------+------+-----+---------+----------------+

4 rows in set (0.00 sec)

if we want to eliminate the column address from employee table then we use Drop command. Syntax:

ALTER TABLE TABLE_NAME DROP COLUMN COLUMN_NAME;

1	ALTER TABLE TABLE_NAME DROP COLUMN COLUMN_NAME;

Drop query

ALTER TABLE employee DROP COLUMN address;

1	ALTER TABLE employee DROP COLUMN address;

Date and Time

February 2, 2023February 2, 2023 by manish

There are various pre defined function for data and time we will see them one by one. If you want to show current time then we use CURTIME().It returns time in HH:MM:SS string format

mysql>SELECT CURTIME();


+-----------+
| CURTIME() |
+-----------+
| 16:06:23  |
+-----------+
1 row in set (0.06 sec)

mysql>SELECT CURTIME();

+-----------+

| CURTIME() |

+-----------+

| 16:06:23 |

+-----------+

1 row in set (0.06 sec)

below is HHMMSS in numeric format

mysql> select CURTIME()+0;
+-------------+
| CURTIME()+0 |
+-------------+
|      162404 |
+-------------+
1 row in set (0.06 sec)

mysql> select CURTIME()+0;

+-------------+

| CURTIME()+0 |

+-------------+

| 162404 |

+-------------+

1 row in set (0.06 sec)

To select current data we use CURDATE().It returns data in YYYY-MM-DD string format. … Read more

Drop command: To eliminate a column from a table.

February 2, 2023February 2, 2023 by bharti

To eliminate a column from table we use drop command. Suppose we have table employee with an extra field Address and we want to eliminate this.

create table student(id int(11) NOT NULL AUTO_INCREMENT,
                     name varchar(40),
                     address varchar(40),
                  PRIMARY KEY(id));

create table student(id int(11) NOT NULL AUTO_INCREMENT,

name varchar(40),

address varchar(40),

PRIMARY KEY(id));

mysql&gt; desc student;
+---------+-------------+------+-----+---------+----------------+
| Field   | Type        | Null | Key | Default | Extra          |
+---------+-------------+------+-----+---------+----------------+
| id      | int(11)     | NO   | PRI | NULL    | auto_increment |
| name    | varchar(40) | YES  |     | NULL    |                |
| address | varchar(40) | YES  |     | NULL    |                |
+---------+-------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)

mysql> desc student;

+---------+-------------+------+-----+---------+----------------+

+---------+-------------+------+-----+---------+----------------+

| id | int(11) | NO | PRI | NULL | auto_increment |

+---------+-------------+------+-----+---------+----------------+

3 rows in set (0.00 sec)

To remove this column we use Drop query. Syntax:

ALTER TABLE table_name drop column_name;

1	ALTER TABLE table_name drop column_name;

ALTER TABLE student drop address;

1	ALTER TABLE student drop address;

mysql&gt; desc student;
+-------+-------------+------+-----+---------+----------------+
| Field | Type        | Null | Key | Default | Extra          |
+-------+-------------+------+-----+---------+----------------+
| id    | int(11)     | NO   | PRI | NULL    | auto_increment |
| name  | varchar(40) | YES  |     | NULL    |                |
+-------+-------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)

mysql> desc student;

+-------+-------------+------+-----+---------+----------------+

+-------+-------------+------+-----+---------+----------------+

| id | int(11) | NO | PRI | NULL | auto_increment |

+-------+-------------+------+-----+---------+----------------+

2 rows in set (0.00 sec)

creating a new user in mysql

February 2, 2023February 2, 2023 by manish

Here we are creating user with name manish and password for manish is password;

CREATE USER 'manish'@'localhost' IDENTIFIED BY 'password';

1	CREATE USER 'manish'@'localhost' IDENTIFIED BY 'password';

Creating a user and force user to change password at first login for that PASSWORD EXPIRE is used.

CREATE USER 'manish'@'localhost' IDENTIFIED BY 'password' PASSWORD EXPIRE;

1	CREATE USER 'manish'@'localhost' IDENTIFIED BY 'password' PASSWORD EXPIRE;

Creating a user and expiring the password after 180 days, PASSWORD EXPIRE INTERVAL 180 DAY is used

CREATE USER 'manish'@'localhost' IDENTIFIED BY 'password'  PASSWORD EXPIRE INTERVAL 180 DAY;

1	CREATE USER 'manish'@'localhost' IDENTIFIED BY 'password' PASSWORD EXPIRE INTERVAL 180 DAY;

Creating a user … Read more

How to add new column in a table?

February 2, 2023February 2, 2023 by bharti

To insert new column in a table we use ALTER query. Syntax:

alter table table_name add column_name data_type;

1	alter table table_name add column_name data_type;

For example, if we consider the table employee we can write the query as:

mysql&gt;alter table employee add city varchar(25) not null;

1	mysql>alter table employee add city varchar(25) not null;

by this query we see that a new column E_City has been added in table Employee.Further you can also insert values in column city by using update … Read more

Changing primary key of table

February 2, 2023February 2, 2023 by manish

We have a table basic profile with following table structure

create table basic_profile(b_id int(10) NOT NULL AUTO_INCREMENT,
                           id1 int(10),
                           id2 int(10),
                          fname varchar(30),
                         lname varchar(30),
                         mailid varchar(50),
                         address varchar(100),
                        primary key(b_id));

create table basic_profile(b_id int(10) NOT NULL AUTO_INCREMENT,

id1 int(10),

id2 int(10),

fname varchar(30),

lname varchar(30),

mailid varchar(50),

address varchar(100),

primary key(b_id));

mysql> desc basic_profile;
+---------+--------------+------+-----+---------+----------------+
| Field   | Type         | Null | Key | Default | Extra          |
+---------+--------------+------+-----+---------+----------------+
| b_id    | int(10)      | NO   | PRI | NULL    | auto_increment |
| id1     | int(10)      | YES  |     | NULL    |                |
| id2     | int(10)      | YES  |     | NULL    |                |
| fname   | varchar(30)  | YES  |     | NULL    |                |
| lname   | varchar(30)  | YES  |     | NULL    |                |
| mailid  | varchar(50)  | YES  |     | NULL    |                |
| address | varchar(100) | YES  |     | NULL    |                |
+---------+--------------+------+-----+---------+----------------+
7 rows in set (0.06 sec)

mysql> desc basic_profile;

+---------+--------------+------+-----+---------+----------------+

+---------+--------------+------+-----+---------+----------------+

| b_id | int(10) | NO | PRI | NULL | auto_increment |

| id1 | int(10) | YES | | NULL | |

| id2 | int(10) | YES | | NULL | |

+---------+--------------+------+-----+---------+----------------+

7 rows in set (0.06 sec)

we don’t want to use it as primary key so first we removed its auto increment the we will remove it from primary key queries for these are

//remove auto increment
ALTER TABLE basic_profile MODIFY b_id INT NOT NULL;

//remove from primary key
//ALTER TABLE TABLE_NAME DROP PRIMARY KEY
ALTER TABLE basic_profile DROP PRIMARY KEY;

//remove auto increment

ALTER TABLE basic_profile MODIFY b_id INT NOT NULL;

//remove from primary key

//ALTER TABLE TABLE_NAME DROP PRIMARY KEY

ALTER TABLE basic_profile DROP PRIMARY KEY;

If you want to make primary key to some other column than we can … Read more

Alter table command to add foreign key

February 2, 2023February 2, 2023 by manish

We have two tables company and location. First table manages company details and second table stores location detail of company. one company can span in multiple location. Initially we have created table for company and location as below.

create table company(id int(11) NOT NULL AUTO_INCREMENT,
                     name varchar(50),
                    description varchar(200),
                  PRIMARY KEY(id));

create table company(id int(11) NOT NULL AUTO_INCREMENT,

name varchar(50),

description varchar(200),

PRIMARY KEY(id));

create table location(id int(11) NOT NULL AUTO_INCREMENT,
                     name varchar(50),
                    address varchar(200),
                   PRIMARY KEY(id));

create table location(id int(11) NOT NULL AUTO_INCREMENT,

name varchar(50),

address varchar(200),

PRIMARY KEY(id));

checking the description of both table

mysql> desc company;
+-------------+--------------+------+-----+---------+----------------+
| Field       | Type         | Null | Key | Default | Extra          |
+-------------+--------------+------+-----+---------+----------------+
| id          | int(11)      | NO   | PRI | NULL    | auto_increment |
| name        | varchar(50)  | YES  |     | NULL    |                |
| description | varchar(200) | YES  |     | NULL    |                |
+-------------+--------------+------+-----+---------+----------------+
3 rows in set (0.09 sec)

mysql> desc company;

+-------------+--------------+------+-----+---------+----------------+

+-------------+--------------+------+-----+---------+----------------+

| id | int(11) | NO | PRI | NULL | auto_increment |

+-------------+--------------+------+-----+---------+----------------+

3 rows in set (0.09 sec)

mysql> desc location;
+---------+--------------+------+-----+---------+----------------+
| Field   | Type         | Null | Key | Default | Extra          |
+---------+--------------+------+-----+---------+----------------+
| id      | int(11)      | NO   | PRI | NULL    | auto_increment |
| name    | varchar(50)  | YES  |     | NULL    |                |
| address | varchar(200) | YES  |     | NULL    |                |
+---------+--------------+------+-----+---------+----------------+
3 rows in set (0.06 sec)

mysql> desc location;

+---------+--------------+------+-----+---------+----------------+

+---------+--------------+------+-----+---------+----------------+

| id | int(11) | NO | PRI | NULL | auto_increment |

+---------+--------------+------+-----+---------+----------------+

3 rows in set (0.06 sec)

Now We find that one company can … Read more

Drop foreign key constraints

February 2, 2023February 2, 2023 by manish

Some times we have to drop the foreign key constraint that already exists, for that we have to first get the foreign key constraint name. To see detailed description of created table we use following query.

SHOW CREATE TABLE location;

1	SHOW CREATE TABLE location;

Result of above query is

mysql> SHOW CREATE TABLE location;
+----------+--------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
-----+
| Table    | Create Table    |
+----------+--------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
-----+
| location | CREATE TABLE `location` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(50) DEFAULT NULL,
  `address` varchar(200) DEFAULT NULL,
  `company_id` int(11) NOT NULL,
  PRIMARY KEY (`id`),
  KEY `company_fk_id` (`company_id`),
  CONSTRAINT `company_fk_id` FOREIGN KEY (`company_id`) REFERENCES `company` (`i
d`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+----------+--------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
-----+
1 row in set (0.08 sec)

mysql> SHOW CREATE TABLE location;

+----------+--------------------------------------------------------------------

--------------------------------------------------------------------------------

-----+

| Table | Create Table |

+----------+--------------------------------------------------------------------

--------------------------------------------------------------------------------

-----+

| location | CREATE TABLE `location` (

`id` int(11) NOT NULL AUTO_INCREMENT,

`name` varchar(50) DEFAULT NULL,

`address` varchar(200) DEFAULT NULL,

`company_id` int(11) NOT NULL,

PRIMARY KEY (`id`),

KEY `company_fk_id` (`company_id`),

CONSTRAINT `company_fk_id` FOREIGN KEY (`company_id`) REFERENCES `company` (`i

d`) ON DELETE CASCADE ON UPDATE CASCADE

) ENGINE=InnoDB DEFAULT CHARSET=latin1 |

+----------+--------------------------------------------------------------------

--------------------------------------------------------------------------------

-----+

1 row in set (0.08 sec)

Here we can see that company_id column is referring company tables id … Read more