Answer / kalpana

Primary key can never be NULL.it is used to uniquely
identify the row in a table.The database engine requeir a
value to relocate the record.so Primary key can never be
NUL.unique key may be NULL.

Answer / sunil kumar

Hello Nivedita,
I am not satisfied with ur answer the difference between
primary key and foreign key.I think the answer is reverse.

Answer / bharanikumar

primary key does not allow null value,
but unique allow only one null value...


www.happylife.in

Answer / amit kumar tiwari

primary key uniquely define each table and never allow NULL
value. But unique key may be NULL value.

Answer / g priya

If a field is null the database engine makes the field to be 0
if not null is specified ,field must be given a value
Primary key is unique,not null,index where as Unique key has
1 null value

Answer / nivedita

IF NULL is specified,the feild is allow to be left empty
without any value.
IF NOT NULL is specified,the field must be given a value. In
the absence of either a NULL or NOT NULL, NULL is assumed.

-------
Unique key can't be NULL.Primary key can be NULL.
Unique key always contain unique value,duplicate are not
allowed(genrally the system genrated key).Primary key maybe
repeated.

How show all tables in mysql query?

0 Answers  

How to use case expression?

0 Answers  

about join

2 Answers  

How do I run a query in mysql?

0 Answers  

Can you shard mysql?

0 Answers  

How to find the unique values if the value in the column is repeated?

0 Answers  

What is DML in MySQL?

1 Answers  

What is mysql sleep process?

0 Answers  

mysql> select * from store; +------+-------+-------+ | id | month | sales | +------+-------+-------+ | 1 | 1 | 100 | | 1 | 2 | 100 | | 1 | 3 | 200 | | 1 | 4 | 300 | | 1 | 5 | NULL | | 1 | 6 | 200 | | 1 | 7 | 800 | | 1 | 8 | 100 | | 1 | 9 | 240 | | 1 | 10 | 140 | | 1 | 11 | 400 | | 1 | 12 | 300 | | 2 | 1 | 300 | | 2 | 2 | 300 | | 2 | 3 | 300 | | 2 | 4 | 200 | | 2 | 5 | 200 | | 2 | 6 | 200 | | 2 | 7 | 100 | | 2 | 8 | 100 | | 2 | 9 | 300 | | 2 | 10 | 100 | | 2 | 11 | 150 | | 2 | 12 | 150 | +------+-------+-------+ this is my table. i need to display output like this. +------+----------+----------+----------+----------+ | id | quarter1 | quarter2 | quarter3 | quarter4 | +------+----------+----------+----------+----------+ | 1 | 400 | 500 | 1140 | 840 | | 2 | 900 | 600 | 500 | 400 | +------+----------+----------+----------+----------+ what single query i have to write for this. i tried this query and it displays like the below mysql> select id,sum(sales) as quarter1,(select sum(sales) from store where mont h>3 and month<7 ) as quarter2,(select sum(sales) from store where month>6 and mo nth<10)as quarter3 from store where month>0 and month<4 group by id; +------+----------+----------+----------+ | id | quarter1 | quarter2 | quarter3 | +------+----------+----------+----------+ | 1 | 400 | 1100 | 1640 | | 2 | 900 | 1100 | 1640 | +------+----------+----------+----------+ 2 rows in set (0.00 sec) tel me how to rectify it.

2 Answers  

What are the functions used to encrypt and decrypt the data present in mysql?

0 Answers  

What is insert query in mysql?

0 Answers  

How to Join tables on common columns.

0 Answers