SQL WHERE command in MySQL table for conditional retrieval of records

SELECT * FROM table_name WHERE condition

WHERE clause is used to collect or update or manage the records from the table based on some specified condition .

Here is the table with few rows.

id	name	class	mark	sex
1	John Deo	Four	75	female
2	Max Ruin	Three	90	male
3	Arnold	Three	55	male
4	Krish Star	Four	60	female
5	John Mike	Four	60	female
6	Alex John	Four	55	male

SELECT query with LIMIT and order by with WHERE condition checking using BETWEEN range

To get only the records of Class Four students.

SELECT * FROM student WHERE  class='Four'

Here is the result

id	name	class	mark	sex
1	John Deo	Four	75	female
4	Krish Star	Four	60	female
5	John Mike	Four	60	female
6	Alex John	Four	55	male
10	Big John	Four	55	female
15	Tade Row	Four	93	male
16	Gimmy	Four	93	male
21	Babby John	Four	69	female
31	Marry Toeey	Four	93	male

This will return all the records from the table name=student of class=Four. This is what we require to get all the records of fourth standard students.

WHERE with AND

More than one condition can be added to the where clause by using various logical expressions like AND, OR, < ( less than ), greater than (> ) etc.
Collect all the records of students of fourth standard who have scored mark more than 70.

SELECT * FROM student WHERE  class='Four' AND  mark >70

id	name	class	mark	sex
1	John Deo	Four	75	female
15	Tade Row	Four	93	male
16	Gimmy	Four	93	male
31	Marry Toeey	Four	93	male

We used quotes for all Non Numeric columns and quotes are not used for numeric fields.
Read more on SQL Logical Operator OR , AND

WHERE with BETWEEN

Return all the records of the student table that have marks within a range.

SELECT * FROM `student` WHERE mark BETWEEN 60 and 70

id	name	class	mark	sex
4	Krish Star	Four	60	female
5	John Mike	Four	60	female
20	Jackly	Nine	65	female
21	Babby John	Four	69	female
34	Gain Toe	Seven	69	male

Using LIKE with WHERE

This search will return us all the records for which inside the name field 'John' is available. John name can be any where within the name column value.

SELECT * FROM `student` WHERE name LIKE '%John%'

id	name	class	mark	sex
1	John Deo	Four	75	female
5	John Mike	Four	60	female
6	Alex John	Four	55	male
7	My John Rob	Fifth	78	male
10	Big John	Four	55	female
21	Babby John	Four	69	female

Aggregate functions

We can use MIN(), SUM(), AVG(),COUNT() and other aggregate functions along with WHERE clause.

SELECT MAX(mark) as max_mark FROM `student` WHERE class='Three'

Number of students who got more or equal to 50 marks in class Four.

SELECT COUNT(*) FROM student WHERE class='Four' AND mark >= 50

Show Number of students, average mark, highest mark, lowest mark of class Three.

SELECT COUNT(*),AVG(mark),MAX(mark),MIN(mark) FROM student WHERE class='Three'

USING IN with WHERE

All records of student of class Fourth and Fifth

SELECT * FROM `student` WHERE class IN ('Four','fifth')

We can exclude a class by using NOT IN.

SELECT * FROM `student` WHERE class NOT IN ('Four','fifth')

Subqueries using WHERE

All details of student who got highest mark by using Subqueries.

SELECT * FROM student WHERE 
 mark =  (SELECT MAX(mark) FROM  student)

Using JOIN

SELECT t1.id, name1 FROM t1 LEFT JOIN t2 on t1.id = t2.id
 WHERE  ISNULL(t2.id)

Updating records by using WHERE condition

Give additional 5 marks to all the students of class Five.

UPDATE student SET mark=mark+5 WHERE class='Five'

PHP code using PDO

PHP PDO connection and collecting records

require "config.php";// database connection

$sql="SELECT * FROM student WHERE class='Four' ";
echo "<table><tr><th>ID</th><th>Name</th>
	<th>Class</th><th>Mark</th></tr>";
foreach($dbo->query($sql) as $row){
echo "<tr><td>$row[id]</td><td>$row[name]</td>
	<td>$row[class]</td><td>$row[mark]</td></tr>";
}
echo "</table>";

Selecting records Case Condition Checking

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Raju	11-04-2013
Can we use Where condition linking more that one table?

wale	23-02-2014
I have 12 tables with the same number of fields and field names. I want to sum one of those fields that have numerical values in all tables. How can I accomplish the task.

Ivan	13-09-2014
Anyone can help me how to resolve this issue?? I am getting a type mismatch with the below syntax... I dont know how to resolve it.. adoCompName.RecordSource = "SELECT * FROM Tbl_Comp_Dtl WHERE CompName = ' * " & Text1.Text & " '" adoCompName.Refresh

SQL WHERE Command