Primarkey: it will not allow null values,duplicate values,primary key is the unique key of a table. A primary key is a column or group of columns that uniquely identify a row. Every table should have a primary key. And a table cannot have more than one primary key Foreign Key: it will allow null values… Read More »
concat function is used to concatenate two strings. See the example Select * from mydoubts_data ————————————- |id | jobid | name | salary | age| ————————————- |1 | 121 | vasanthan| 2000 |32 | |2 | 122 | John | 3000 |28 | |3 | 123 | Kiran | 3400 |24 | |4 | 154… Read More »
if you give RAND() in the query it will generate random number between 0 and 1 Eg:Select RAND() from mydoubts_data; ————– RAND() ————- 0.454545 ———— select * from mydoubts_data; ——————– name | salary | ——————– vasanthan | 2000 | John | 3000 | Kiran | 6800 | Raju | 5706 select * from mydoubts_data order… Read More »
see the example below Select * from mydoubts_data ————————————- |id | jobid | name | salary | age| ————————————- |1 | 121 | vasanthan| 2000 |16 | |2 | 122 | John | 3000 |64 | select id,name,salary,SQRT(age) from mydoubts_data ——————————————- |id | jobid | name | salary | SQRT(age)| ——————————————- |1 | 121 |… Read More »
This function used to find the sum of fields in various records See the example below Select * from mydoubts_data ————————————- |id | jobid | name | salary | age| ————————————- |1 | 121 | vasanthan| 2000 |32 | |2 | 122 | John | 3000 |28 | |3 | 123 | Kiran | 3400… Read More »
using AVG function will return the average value of particular fields. Example: Select * from mydoubts_data ————————————- |id | jobid | name | salary | age| ————————————- |1 | 121 | vasanthan| 2000 |32 | |2 | 122 | John | 3000 |28 | |3 | 123 | Kiran | 3400 |24 | |4 |… Read More »
This function using to find out the maximum value in a recordset Select * from mydoubts_data ————————————- |id | jobid | name | salary | age| ————————————- |1 | 121 | vasanthan| 2000 |31 | |2 | 122 | John | 3000 |29 | |3 | 123 | Kiran | 3400 |22 | |4 |… Read More »
counting the number of records in a table. Example: Select * from mydoubts_table; ———————————— |firstname | lastname | address | ———————————— |vasanthan | pv | india | |nazar | gt | texas | |raju | raina | sreelanka| |gt | nazar | texas | |Martin | jacob | Dubai | |mydoubts.in | | newyork |… Read More »
union means joining more than tables.It will not create problems if tables having different columns Example: Suppose we have three tables as below Select * from mydoubts_personal; ———————————— |firstname | lastname | address | ———————————— |vasanthan | pv | india | |nazar | gt | texas | ————————————- Select * from mydoubts_buisness ————————————- |last_name |… Read More »
This clause will replace greater/less than conditions Example: Select * from mydoubts_data ————————————- |id | jobid | name | salary | age| ————————————- |1 | 121 | vasanthan| 2000 |31 | |2 | 122 | John | 3000 |29 | |3 | 123 | Kiran | 3400 |22 | |4 | 154 | Raju |… Read More »