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SQL – ifnull() Example, ifnull() function

admin — Sat, 28 Nov 2009 09:27:39 +0000

SQL ifnull() function is used find null value in rows and returns value on our condition if null value found in column from database table name, otherwise if column value is not null it will return column value.

SQL ifnull() query example explains how to use ifnull() query in SQL.

Table class_name with all records without desired column name sorting

+---------+-------------+------------+------------+
| Roll_No | Name        | Class_Name | Year_Start |
+---------+-------------+------------+------------+
|       1 | Amit Mishra | B.Science  |       2005 |
|       2 | Robot       | B.Tech     |       2005 |
|       3 | Rohan       | M.Tech     |       2005 |
|       4 | Vivek       | B.Tech     |       2009 |
|       5 | Chander     | B.Science  |       2009 |
|       6 | Deepak      | B.Science  |       2009 |
|       7 | Gagan Deep  | B.Tech     |       NULL |
|       8 | Mohit Garg  | M.Tech     |       NULL |
+---------+-------------+------------+------------+

ifnull() examples

SELECT  Name, Year_Start, IFNULL(Year_Start,0) FROM class_name c;

Output

+-------------+------------+----------------------+
| Name        | Year_Start | IFNULL(Year_Start,0) |
+-------------+------------+----------------------+
| Amit Mishra |       2005 |                 2005 |
| Robot       |       2005 |                 2005 |
| Rohan       |       2005 |                 2005 |
| Vivek       |       2009 |                 2009 |
| Chander     |       2009 |                 2009 |
| Deepak      |       2009 |                 2009 |
| Gagan Deep  |       NULL |                    0 |
| Mohit Garg  |       NULL |                    0 |
+-------------+------------+----------------------+

SELECT  Name, Year_Start, IFNULL(Year_Start,2000) FROM class_name c;

Output

+-------------+------------+-------------------------+
| Name        | Year_Start | IFNULL(Year_Start,2000) |
+-------------+------------+-------------------------+
| Amit Mishra |       2005 |                    2005 |
| Robot       |       2005 |                    2005 |
| Rohan       |       2005 |                    2005 |
| Vivek       |       2009 |                    2009 |
| Chander     |       2009 |                    2009 |
| Deepak      |       2009 |                    2009 |
| Gagan Deep  |       NULL |                    2000 |
| Mohit Garg  |       NULL |                    2000 |
+-------------+------------+-------------------------+

SQL – isnull() Example, isnull() function

admin — Sat, 28 Nov 2009 09:08:45 +0000

SQL isnull() function is used find null value in rows and returns 0 (zero) on if null value found in column from database table name, otherwise if column value is not null it will return 1 value. null value will replace automatically with zero value.

SQL isnull() query example explains how to use isnull() query in SQL.

Table class_name with all records without desired column name sorting

+---------+-------------+------------+------------+
| Roll_No | Name        | Class_Name | Year_Start |
+---------+-------------+------------+------------+
|       1 | Amit Mishra | B.Science  |       2005 |
|       2 | Robot       | B.Tech     |       2005 |
|       3 | Rohan       | M.Tech     |       2005 |
|       4 | Vivek       | B.Tech     |       2009 |
|       5 | Chander     | B.Science  |       2009 |
|       6 | Deepak      | B.Science  |       2009 |
|       7 | Gagan Deep  | B.Tech     |       NULL |
|       8 | Mohit Garg  | M.Tech     |       NULL |
+---------+-------------+------------+------------+

isnull() examples

SELECT  Name, Year_Start, ISNULL(Year_Start) FROM class_name c;

Output

+-------------+------------+--------------------+
| Name        | Year_Start | ISNULL(Year_Start) |
+-------------+------------+--------------------+
| Amit Mishra |       2005 |                  0 |
| Robot       |       2005 |                  0 |
| Rohan       |       2005 |                  0 |
| Vivek       |       2009 |                  0 |
| Chander     |       2009 |                  0 |
| Deepak      |       2009 |                  0 |
| Gagan Deep  |       NULL |                  1 |
| Mohit Garg  |       NULL |                  1 |
+-------------+------------+--------------------+

SQL – Select distinct Example, distinct statement

admin — Sat, 28 Nov 2009 08:23:13 +0000

SQL distinct clause is used to remove duplicate rows from database table name. distinct keyword can be used on one column name and more than one column name in SQL query. distinct clause can be implemented in MySQL, oracle, db2, Microsoft SQL server.

SQL distinct query example explains how to use distinct query in SQL.

Table class_name with all records without desired column name sorting

+---------+-------------+------------+------------+
| Roll_No | Name        | Class_Name | Year_Start |
+---------+-------------+------------+------------+
|       1 | Amit Mishra | B.Science  |       2005 |
|       2 | Robot       | B.Tech     |       2005 |
|       3 | Rohan       | M.Tech     |       2005 |
|       4 | Vivek       | B.Tech     |       2009 |
|       5 | Chander     | B.Science  |       2009 |
|       6 | Deepak      | B.Science  |       2009 |
|       7 | Gagan Deep  | B.Tech     |       NULL |
|       8 | Mohit Garg  | M.Tech     |       NULL |
+---------+-------------+------------+------------+

syntax of SQL distinct

SELECT distinct columns FROM table_name

distinct examples

SELECT distinct Roll_No, Name, Class_Name, Year_Start FROM class_name c;

Output

+---------+-------------+------------+------------+
| Roll_No | Name        | Class_Name | Year_Start |
+---------+-------------+------------+------------+
|       1 | Amit Mishra | B.Science  |       2005 |
|       2 | Robot       | B.Tech     |       2005 |
|       3 | Rohan       | M.Tech     |       2005 |
|       4 | Vivek       | B.Tech     |       2009 |
|       5 | Chander     | B.Science  |       2009 |
|       6 | Deepak      | B.Science  |       2009 |
|       7 | Gagan Deep  | B.Tech     |       NULL |
|       8 | Mohit Garg  | M.Tech     |       NULL |
+---------+-------------+------------+------------+

this SQL query returns all rows return because no duplicate row is found. all column name is distinct

SELECT distinct Class_Name, Year_Start FROM class_name;

Output

+------------+------------+
| Class_Name | Year_Start |
+------------+------------+
| B.Science  |       2005 |
| B.Tech     |       2005 |
| M.Tech     |       2005 |
| B.Tech     |       2009 |
| B.Science  |       2009 |
| B.Tech     |       NULL |
| M.Tech     |       NULL |
+------------+------------+

this SQL query returns those row which column name (Class_Name, Year_Start) not duplicate rows value only from table.

SELECT distinct Class_Name FROM class_name;

Output

+------------+
| Class_Name |
+------------+
| B.Science  |
| B.Tech     |
| M.Tech     |
+------------+

this SQL query check distinct on only one column name Class_Name and check duplicate rows in Class_Name column name and remove duplicate rows.

* indicates fetch all columns records from table.

SQL – Select is null Example, is not null Example

admin — Sat, 28 Nov 2009 07:52:14 +0000

SQL is null clause, is not null clause option can filter records from database table name on null value in rows. This returns only null rows which we put is null clause in query, and returns those rows which not having null in row on is not null clause. null keyword can be used on one column name and more than one column name in SQL query. null clause can be implemented in MySQL, oracle, db2, Microsoft SQL server.

SQL null query example explains how to use null query in SQL.

Table class_name with all records without desired column name sorting

+---------+-------------+------------+------------+
| Roll_No | Name        | Class_Name | Year_Start |
+---------+-------------+------------+------------+
|       1 | Amit Mishra | B.Science  |       2005 |
|       2 | Robot       | B.Tech     |       2005 |
|       3 | Rohan       | M.Tech     |       2005 |
|       4 | Vivek       | B.Tech     |       2009 |
|       5 | Chander     | B.Science  |       2009 |
|       6 | Deepak      | B.Science  |       2009 |
|       7 | Gagan Deep  | B.Tech     |       NULL |
|       8 | Mohit Garg  | M.Tech     |       NULL |
+---------+-------------+------------+------------+

Where clause

SELECT * FROM class_name  where Year_Start is null;

Output

+---------+------------+------------+------------+
| Roll_No | Name       | Class_Name | Year_Start |
+---------+------------+------------+------------+
|       7 | Gagan Deep | B.Tech     |       NULL |
|       8 | Mohit Garg | M.Tech     |       NULL |
+---------+------------+------------+------------+

this SQL query returns those row which column name (Year_Start) having null value only from table.

SELECT * FROM class_name  where Year_Start is not null;

Output

+---------+-------------+------------+------------+
| Roll_No | Name        | Class_Name | Year_Start |
+---------+-------------+------------+------------+
|       1 | Amit Mishra | B.Science  |       2005 |
|       2 | Robot       | B.Tech     |       2005 |
|       3 | Rohan       | M.Tech     |       2005 |
|       4 | Vivek       | B.Tech     |       2009 |
|       5 | Chander     | B.Science  |       2009 |
|       6 | Deepak      | B.Science  |       2009 |
+---------+-------------+------------+------------+

this SQL query returns those row which column name (Year_Start) not having null value only from table.

* indicates fetch all columns records from table.

SQL – Select Where clause Example

admin — Sat, 28 Nov 2009 07:25:07 +0000

SQL where clause option can filter records from database table name. This returns only required rows which we put clause in query. where keyword can be used on one column name and more than one column name in SQL query. where clause can be implemented in MySQL, oracle, db2, Microsoft SQL server.

SQL select where query example explains how to use select where query in SQL.

Table class_name with all records without desired column name sorting

+---------+-------------+------------+------------+
| Roll_No | Name        | Class_Name | Year_Start |
+---------+-------------+------------+------------+
|       1 | Amit Mishra | B.Science  |       2005 |
|       2 | Robot       | B.Tech     |       2005 |
|       3 | Rohan       | M.Tech     |       2005 |
|       4 | Vivek       | B.Tech     |       2009 |
|       5 | Chander     | B.Science  |       2009 |
|       6 | Deepak      | B.Science  |       2009 |
+---------+-------------+------------+------------+

Where clause

SELECT * FROM class_name c where Year_Start = 2005;

Output

+---------+-------------+------------+------------+
| Roll_No | Name        | Class_Name | Year_Start |
+---------+-------------+------------+------------+
|       1 | Amit Mishra | B.Science  |       2005 |
|       2 | Robot       | B.Tech     |       2005 |
|       3 | Rohan       | M.Tech     |       2005 |
+---------+-------------+------------+------------+

this SQL query returns those row which column name (Year_Start) having 2005 value only from table.

select * from class_name where Year_Start > 2005;

Output

+---------+---------+------------+------------+
| Roll_No | Name    | Class_Name | Year_Start |
+---------+---------+------------+------------+
|       4 | Vivek   | B.Tech     |       2009 |
|       5 | Chander | B.Science  |       2009 |
|       6 | Deepak  | B.Science  |       2009 |
+---------+---------+------------+------------+

this SQL query returns only those row in column Year_Start greater than 2005 value only.

group by on more than one column name

SELECT * FROM class_name c
   where Year_Start= 2005 and Class_Name = 'B.Tech';

Output

+---------+-------+------------+------------+
| Roll_No | Name  | Class_Name | Year_Start |
+---------+-------+------------+------------+
|       2 | Robot | B.Tech     |       2005 |
+---------+-------+------------+------------+

this SQL query returns only those row in column Year_Start having 2005 value only and also class_name column value having B.Tech.

* indicates fetch all columns records from table.

SQL – Select Group By Example, Group by statement

admin — Sat, 28 Nov 2009 06:56:11 +0000

SQL Group by column name clause is used to give aggregate records in database table. Group by keyword is used to give records in same column rows in grouped manner. Group by can be used on one column name and more than one column name in SQL query. group by can be implemented in MySQL, oracle, db2, Microsoft SQL server.

SQL select Group by query example explains how to use select Group by query in SQL.

Table class_name with all records without desired column name sorting

+---------+-------------+------------+------------+
| Roll_No | Name        | Class_Name | Year_Start |
+---------+-------------+------------+------------+
|       1 | Amit Mishra | B.Science  |       2005 |
|       2 | Robot       | B.Tech     |       2005 |
|       3 | Rohan       | M.Tech     |       2005 |
|       4 | Vivek       | B.Tech     |       2009 |
|       5 | Chander     | B.Science  |       2009 |
|       6 | Deepak      | B.Science  |       2009 |
+---------+-------------+------------+------------+

Group by

SELECT * FROM class_name c group by Class_Name;

Output

+---------+-------------+------------+------------+
| Roll_No | Name        | Class_Name | Year_Start |
+---------+-------------+------------+------------+
|       1 | Amit Mishra | B.Science  |       2005 |
|       2 | Robot       | B.Tech     |       2005 |
|       3 | Rohan       | M.Tech     |       2005 |
+---------+-------------+------------+------------+

this SQL query returns unique column name (class_name) rows only from table.

SELECT Roll_No, Name, Class_Name, count(Class_Name)
           FROM class_name c group by Class_Name;

Output

+---------+-------------+------------+-------------------+
| Roll_No | Name        | Class_Name | count(Class_Name) |
+---------+-------------+------------+-------------------+
|       1 | Amit Mishra | B.Science  |                 3 |
|       2 | Robot       | B.Tech     |                 2 |
|       3 | Rohan       | M.Tech     |                 1 |
+---------+-------------+------------+-------------------+

this SQL query returns unique column name (class_name) rows only from table and it shows count of unique column name.

group by on more than one column name

SELECT * FROM class_name c group by Class_Name,Year_Start;

Output

+---------+-------------+------------+------------+
| Roll_No | Name        | Class_Name | Year_Start |
+---------+-------------+------------+------------+
|       1 | Amit Mishra | B.Science  |       2005 |
|       5 | Chander     | B.Science  |       2009 |
|       2 | Robot       | B.Tech     |       2005 |
|       4 | Vivek       | B.Tech     |       2009 |
|       3 | Rohan       | M.Tech     |       2005 |
+---------+-------------+------------+------------+

this SQL query returns, unique column name rows only with two columns

* indicates fetch all columns records from table.

SQL – Select Order by clause keyword

admin — Tue, 24 Nov 2009 15:16:12 +0000

SQL select query is used to fetch records from database. order by column name clause is used to sorting records in database table. Order by keyword is having options for sorting data records, one is ascending sorting order, Second is descending order, it will return records in higher to lower order. In ascending sorting order, it returns records in lower to higher order. order by clause can be implemented on all database Oracle, MS Sql (Microsoft SQL), MySQL.

SQL select order by query example explains how to use select order by query in SQL.

Table class_name with all records without desired column name sorting

+---------+-------------+------------+------------+
| Roll_No | Name        | Class_Name | Year_Start |
+---------+-------------+------------+------------+
|       1 | Amit Mishra | B Science  |       2005 |
|       2 | Robot       | B.Tech     |       2005 |
|       3 | Rohan       | M.Tech     |       2005 |
|       4 | Vivek       | B.Tech     |       2009 |
|       5 | Chander     | B.Science  |       2009 |
|       6 | Deepak      | B.Science  |       2009 |
+---------+-------------+------------+------------+

Descending Order by Sorting

SELECT * FROM class_name c order by name desc;

Output

+---------+-------------+------------+------------+
| Roll_No | Name        | Class_Name | Year_Start |
+---------+-------------+------------+------------+
|       4 | Vivek       | B.Tech     |       2009 |
|       3 | Rohan       | M.Tech     |       2005 |
|       2 | Robot       | B.Tech     |       2005 |
|       6 | Deepak      | B.Science  |       2009 |
|       5 | Chander     | B.Science  |       2009 |
|       1 | Amit Mishra | B Science  |       2005 |
+---------+-------------+------------+------------+

this SQL query in sql return rows from higher to lower sorting order from table.

SELECT * FROM class_name c order by name asc;

Output

+---------+-------------+------------+------------+
| Roll_No | Name        | Class_Name | Year_Start |
+---------+-------------+------------+------------+
|       1 | Amit Mishra | B Science  |       2005 |
|       5 | Chander     | B.Science  |       2009 |
|       6 | Deepak      | B.Science  |       2009 |
|       2 | Robot       | B.Tech     |       2005 |
|       3 | Rohan       | M.Tech     |       2005 |
|       4 | Vivek       | B.Tech     |       2009 |
+---------+-------------+------------+------------+

this SQL query in sql return rows from lower to higher sorting order from table.

* indicates fetch all columns records from table.

SQL – Select with Temporary Dual table

admin — Sun, 22 Nov 2009 11:11:30 +0000

SQL select query is used to fetch records from database. Dual table is Temporary table which is created for temporary work. Dual table allow people to use from keyword in query.

SQL select dual example explains how to use select dual query in SQL.

select 3+1 from dual;

Table dual with records

+-----+
| 3+1 |
+-----+
|   4 |
+-----+

SQL – Select with limit rows and records Clause Example, Oracle MS SQL MySQL

admin — Sun, 22 Nov 2009 10:58:21 +0000

SQL select query is used to fetch records from database. limit clause is used to get limited rows from database table. Limit is implemented differently with different database Oracle, MS Sql, MySQL.

SQL select limit query example explains how to use select limit query in SQL.

Table class_name with all records

+---------+-------------+------------+------------+
| Roll_No | Name        | Class_Name | Year_Start |
+---------+-------------+------------+------------+
|       1 | Amit Mishra | B Science  |       2005 |
|       2 | Robot       | B.Tech     |       2005 |
|       3 | Rohan       | M.Tech     |       2005 |
|       4 | Vivek       | B.Tech     |       2009 |
|       5 | Chander     | B.Science  |       2009 |
|       6 | Deepak      | B.Science  |       2009 |
+---------+-------------+------------+------------+

In MySQL, limit keyword

select * from class_name limit 4;

Output

+---------+-------------+------------+------------+
| Roll_No | Name        | Class_Name | Year_Start |
+---------+-------------+------------+------------+
|       1 | Amit Mishra | B Science  |       2005 |
|       2 | Robot       | B.Tech     |       2005 |
|       3 | Rohan       | M.Tech     |       2005 |
|       4 | Vivek       | B.Tech     |       2009 |
+---------+-------------+------------+------------+

this SQL query in mysql return only top 4 rows from table.

select * from class_name limit 2, 4;

Output

+---------+---------+------------+------------+
| Roll_No | Name    | Class_Name | Year_Start |
+---------+---------+------------+------------+
|       3 | Rohan   | M.Tech     |       2005 |
|       4 | Vivek   | B.Tech     |       2009 |
|       5 | Chander | B.Science  |       2009 |
|       6 | Deepak  | B.Science  |       2009 |
+---------+---------+------------+------------+

this SQL query in mysql returns only rows start after top 2 and get only 4 rows.

In Oracle, limits rows by rownum keyword in SQL query

select * from class_name rownum <=4;

this Oracle SQL query returns only top 4 rows from table

In Microsoft SQL, limits rows by top keyword in SQL query

select top 4 column_names from class_name;

this Mircrosoft SQL query returns only top 4 rows from table

* indicates fetch all columns records from table.

SQL – Select Query with Clause Example

admin — Sun, 22 Nov 2009 07:46:05 +0000

SQL select query is used to fetch records from database. Select can use with clause and without clause. Select query returns number of rows from table. Select query can allow clause with where keyword. where clause is used for filter rows in database table.

SQL select clause query example explains how to use select clause query in SQL.

Table class_name with all records

+---------+-------------+------------+------------+
| Roll_No | Name        | Class_Name | Year_Start |
+---------+-------------+------------+------------+
|       1 | Amit Mishra | B Science  |       2005 |
|       2 | Robot       | B.Tech     |       2005 |
|       3 | Rohan       | M.Tech     |       2005 |
|       4 | Vivek       | B.Tech     |       2009 |
|       5 | Chander     | B.Science  |       2009 |
|       6 | Deepak      | B.Science  |       2009 |
+---------+-------------+------------+------------+

where clause to find equals to

select * from class_name where Class_Name = 'B.Tech';

select * from class_name where Class_Name <=> 'B.Tech';

Output

+---------+-------+------------+------------+
| Roll_No | Name  | Class_Name | Year_Start |
+---------+-------+------------+------------+
|       2 | Robot | B.Tech     |       2005 |
|       4 | Vivek | B.Tech     |       2009 |
+---------+-------+------------+------------+

returns only those row having class_name with B.Tech only

where clause to find not equals to

select * from class_name where Class_Name != 'B.Tech';

select * from class_name where Class_Name <> 'B.Tech';

Output

+---------+-------------+------------+------------+
| Roll_No | Name        | Class_Name | Year_Start |
+---------+-------------+------------+------------+
|       1 | Amit Mishra | B Science  |       2005 |
|       3 | Rohan       | M.Tech     |       2005 |
|       5 | Chander     | B.Science  |       2009 |
|       6 | Deepak      | B.Science  |       2009 |
+---------+-------------+------------+------------+

returns only those row not having class_name with B.Tech only

where clause to find less than to

select * from class_name where Year_Start < 2009;

Output

+---------+-------------+------------+------------+
| Roll_No | Name        | Class_Name | Year_Start |
+---------+-------------+------------+------------+
|       1 | Amit Mishra | B Science  |       2005 |
|       2 | Robot       | B.Tech     |       2005 |
|       3 | Rohan       | M.Tech     |       2005 |
+---------+-------------+------------+------------+

returns only those row in column Year_Start less than 2009 value only

where clause to find greater than to

select * from class_name where Year_Start > 2005;

Output

+---------+---------+------------+------------+
| Roll_No | Name    | Class_Name | Year_Start |
+---------+---------+------------+------------+
|       4 | Vivek   | B.Tech     |       2009 |
|       5 | Chander | B.Science  |       2009 |
|       6 | Deepak  | B.Science  |       2009 |
+---------+---------+------------+------------+

returns only those row in column Year_Start greater than 2005 value only

* indicates fetch all columns records from table.