Where clause in MySQL
Hello and
welcome everyone. In this article, we will learn about the WHERE clause in
MySQL. Let’s go.
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MySQL
WHERE clause is used to get specific result from the database table with
specific condition as well as it filter records. You can use WHERE clause with
SELECT statement as well as DELETE and UPDATE statement.
Syntax:
With
SELECT statement syntax:
SELECT *
FROM table_name
WHERE
condition;
Here is
SELECT –
this command retrieve data from the database table.
table_name
– this is table name which table data you want to retrieve.
WHERE –
this WHERE clause using specific record will retrieve.
condition
– specify the condition for the update.
With
UPDATE statement syntax:
UPDATE table_name
SET column_name = values, …
WHERE condition;
Here is
UPDATE –
this command updates the values or data or records in the table.
table_name
– this is table name which table data you want to update.
SET – it
specifies which columns record you want to update with the new values. For
update, many rows record you can use a comma separated.
column_name
– this column name is which column records you want to update.
values –
this one is you can set new values for an update on previous values.
WHERE –
this WHERE clause using specific record will update.
condition
– specify the condition for the update.
With
DELETE statement syntax:
DELETE FROM
table_name
WHERE condition
Here is
DELETE
FROM – it is a delete rows data command in MySQL
table_name – which tables
row data you want to delete then specify the table name here.
WHERE
condition – if you want to specific row delete then use WHERE condition. If the
condition matches with rows then it will be deleted otherwise MySQL fetch
error.
For
Example:
Here is
the, we will create a table for an employee in the database.
CREATE
TABLE IF NOT EXISTS employee (
e_id
int (10) PRIMARY KEY,
e_firstname
varchar (50) NOT NULL,
e_lastname
varchar (50) NOT NULL,
e_age
int (10),
e_city
varchar (250)
e_sex
char (1)
e_phnumber
int (15) NOT NULL
)
Here we
insert record in the employee table.
INSERT INTO employee (
‘e_id’, ’e_firstname’, ’e_lastname’,
’e_age’, ’e_city’, ’e_sex’,
’e_phnumber’
)
VALUES
(
1, ‘Hone’, ‘Reus’, 25, ‘San Jose’, ‘M’, ‘ +
1 555 555 1111’
),
(
2, ‘Cries’, ’Fence’, 23, ’Fresno’, ’F’, ’
+1 555 555 1111’
);
Final
Result
‘e_id’ ’e_firstname’ ’e_lastname’ ’e_age’ ’e_city’ ’e_sex’ ’e_phnumber’
1 Hone Reus 25 San Jose M +1 555 555 1111
2 Cries Fence 23 Fresno F +1 555 555 1111
With
SELECT statement example:
SELECT
e_id, e_firstname,
e_lastname FROM employee
WHERE Age > 20;
With
UPDATE statement example:
UPDATE employee
SET e_age = 26, e_city = ‘Oakland’
WHERE e_id = 2;
Then it
will update record.
‘e_id’ ’e_firstname’ ’e_lastname’ ’e_age’ ’e_city’ ’e_sex’ ’e_phnumber’
2 Cries Fence 26 Oakland F +1 555 555 1111
With
DELETE statement example:
DELETE FROM employee
WHERE e_age = ‘23’;
After
executing above query then row number 2 will deleted.
In this
article, we learned about WHERE clause. You can use WHERE clause with SELECT,
DELETE, and UPDATE statement.
MongoDB with .Net Core course link => https://www.udemy.com/mongodb-with-net-core-sagar-jaybhay/
C# basic course click on: https://www.udemy.com/learn-csharp-with-sagar-jaybhay/
Web API 2- .Net Core In depth In 5 Hours
click on: https://www.udemy.com/web-api-2-net-core-in-depth-in-5-hrs-with-sagar-jaybhay/
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