SQL DELETE Statement

The DELETE statement is used to delete rows in a table.

SQL DELETE Syntax

DELETE FROM table_name
WHERE some_column=some_value; 

 

Example

DELETE FROM Customers
WHERE CustomerName='Alfreds Futterkiste' AND ContactName='Maria Anders'; 

 

Delete All Data

It is possible to delete all rows in a table without deleting the table. This means that the table structure, attributes, and indexes will be intact:

DELETE FROM table_name;

or

DELETE * FROM table_name;

 

 

SQL INSERT INTO, and Update Statements

SQL INSERT INTO Syntax

It is possible to write the INSERT INTO statement in two forms.
The first form does not specify the column names where the data will be inserted, only their values:

INSERT INTO table_name
VALUES (value1,value2,value3,...);

 

The second form specifies both the column names and the values to be inserted:

INSERT INTO table_name (column1,column2,column3,...)
VALUES (value1,value2,value3,...);

 

"Customers" table:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
87	Wartian Herkku	Pirkko Koskitalo	Torikatu 38	Oulu	90110	Finland
88	Wellington Importadora	Paula Parente	Rua do Mercado, 12	Resende	08737-363	Brazil
89	White Clover Markets	Karl Jablonski	305 - 14th Ave. S. Suite 3B	Seattle	98128	USA
90	Wilman Kala	Matti Karttunen	Keskuskatu 45	Helsinki	21240	Finland
91	Wolski	Zbyszek	ul. Filtrowa 68	Walla	01-012	Poland

 

Example

INSERT INTO Customers (CustomerName, ContactName, Address, City, PostalCode, Country)
VALUES ('Cardinal','Tom B. Erichsen','Skagen 21','Stavanger','4006','Norway'); 

 

The selection from the "Customers" table will now look like this:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
87	Wartian Herkku	Pirkko Koskitalo	Torikatu 38	Oulu	90110	Finland
88	Wellington Importadora	Paula Parente	Rua do Mercado, 12	Resende	08737-363	Brazil
89	White Clover Markets	Karl Jablonski	305 - 14th Ave. S. Suite 3B	Seattle	98128	USA
90	Wilman Kala	Matti Karttunen	Keskuskatu 45	Helsinki	21240	Finland
91	Wolski	Zbyszek	ul. Filtrowa 68	Walla	01-012	Poland
92	Cardinal	Tom B. Erichsen	Skagen 21	Stavanger	4006	Norway

 

 

Insert Data Only in Specified Columns

It is also possible to only insert data in specific columns.
The following SQL statement will insert a new row, but only insert data in the "CustomerName", "City", and "Country" columns (and the CustomerID field will of course also be updated automatically):

Example

INSERT INTO Customers (CustomerName, City, Country)
VALUES ('Cardinal', 'Stavanger', 'Norway');

 

The UPDATE statement is used to update existing records in a table.

SQL UPDATE Syntax

UPDATE table_name
SET column1=value1,column2=value2,...
WHERE some_column=some_value;

 

"Customers" table:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK
5	Berglunds snabbköp	Christina Berglund	Berguvsvägen 8	Luleå	S-958 22	Sweden

---

SQL UPDATE Example

Assume we wish to update the customer "Alfreds Futterkiste" with a new contact person and city.
We use the following SQL statement:

Example

UPDATE Customers
SET ContactName='Alfred Schmidt', City='Hamburg'
WHERE CustomerName='Alfreds Futterkiste';

 

SQL WHERE AND & OR Operators Syntax ORDER BY Keyword

SELECT column_name,column_name
FROM table_name
WHERE column_name operator value;

Below is a selection from the "Customers" table:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK
5	Berglunds snabbköp	Christina Berglund	Berguvsvägen 8	Luleå	S-958 22	Sweden

---

WHERE Clause Example

The following SQL statement selects all the customers from the country "Mexico", in the "Customers" table:

Example

SELECT * FROM Customers
WHERE Country='Mexico';

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico

AND & OR Operators

Example

SELECT * FROM Customers
WHERE Country='Germany'
AND City='Berlin'; 

Number of Records: 1

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany

OR Operator Example

The following SQL statement selects all customers from the city "Berlin" OR "München", in the "Customers" table: 

Example

SELECT * FROM Customers
WHERE City='Berlin'
OR City='München'; 

Number of Records:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany

Combining AND & OR

You can also combine AND and OR (use parenthesis to form complex expressions).
The following SQL statement selects all customers from the country "Germany" AND the city must be equal to "Berlin" OR "München", in the "Customers" table:

Example

SELECT * FROM Customers
WHERE Country='Germany'
AND (City='Berlin' OR City='München');

SQL ORDER BY Syntax

SELECT column_name, column_name
FROM table_name
ORDER BY column_name ASC|DESC, column_name ASC|DESC;

ORDER BY Example

The following SQL statement selects all customers from the "Customers" table, sorted by the "Country" column:

Example

SELECT * FROM Customers
ORDER BY Country;

ORDER BY DESC Example

The following SQL statement selects all customers from the "Customers" table, sorted DESCENDING by the "Country" column:

Example

SELECT * FROM Customers
ORDER BY Country DESC;

ORDER BY Several Columns Example

The following SQL statement selects all customers from the "Customers" table, sorted by the "Country" and the "CustomerName" column:

Example

SELECT * FROM Customers
ORDER BY Country, CustomerName;

 

ORDER BY Several Columns Example 2

The following SQL statement selects all customers from the "Customers" table, sorted ascending by the "Country" and descending by the "CustomerName" column:

Example

SELECT * FROM Customers
ORDER BY Country ASC, CustomerName DESC;

 

SQL SELECT DISTINCT Syntax

SQL SELECT DISTINCT Syntax

SELECT DISTINCT column_name,column_name
FROM table_name;

 

"Customers" table:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK
5	Berglunds snabbköp	Christina Berglund	Berguvsvägen 8	Luleå	S-958 22	Sweden

Example

SELECT DISTINCT City FROM Customers;

 

SQL Quereis SELECT * FROM Customers;

"Customers" table:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK
5	Berglunds snabbköp	Christina Berglund	Berguvsvägen 8	Luleå	S-958 22	Sweden

The table above contains five records (one for each customer) and seven columns (CustomerID, CustomerName, ContactName, Address, City, PostalCode, and Country).

Some of The Most Important SQL Commands

• SELECT - extracts data from a database
• UPDATE - updates data in a database
• DELETE - deletes data from a database
• INSERT INTO - inserts new data into a database
• CREATE DATABASE - creates a new database
• ALTER DATABASE - modifies a database
• CREATE TABLE - creates a new table
• ALTER TABLE - modifies a table
• DROP TABLE - deletes a table
• CREATE INDEX - creates an index (search key)
• DROP INDEX - deletes an index 

The following SQL statement selects all the records in the "Customers" table:

 SELECT * FROM Customers; 

SQL is NOT case sensitive: select is the same as SELECT

Semicolon is the standard way to separate each SQL statement in database systems that allow more than one SQL statement to be executed in the same call to the server

SQL SELECT Syntax

SELECT column_name,column_name
FROM table_name;

 

SELECT * FROM table_name;

 

SELECT Column Example

The following SQL statement selects the "CustomerName" and "City" columns from the "Customers" table:

Example

SELECT CustomerName,City FROM Customers;

 

SELECT * Example

The following SQL statement selects all the columns from the "Customers" table:

Example

SELECT * FROM Customers;

PHP MySQL HTML Code: Create database & Create Table, Add, edit Search...

PHP MySQL HTML Code: Create database & Create Table, Add, edit Search...: create database DBname; CREATE TABLE people (name VARCHAR(30), age INTEGER, height FLOAT, date DATETIME); INSERT INTO people VALUES (...

Create database & Create Table, Add, edit Search Delete in MySQL

create database DBname;

CREATE TABLE people (name VARCHAR(30), age INTEGER, height FLOAT, date DATETIME);

INSERT INTO people VALUES ( "Jim", 45, 1.75, "2006-02-02 15:35:00" ), ( "Peggy", 6, 1.12, "2006-03-02 16:21:00" )


UPDATE people SET age = 7, date = "2006-06-02 16:21:00", height = 1.22 WHERE name = "Peggy"
SELECT name FROM people WHERE age < 12
DELETE FROM people WHERE age < 12