In this chapter we will devote ourselves to explain the language SQL since later we will use it very much in the PHP connections with MySQL.

Creation and modification of Stage in SQL

MySQL is organized from stage and the above mentioned stage contains fields. Every field is capable of containing a type of fact. The types of information that it is possible to create in the language SQL are:

To create a table we will use the following syntax:

ONE BELIEVE TABLE Nombre_tabla
(Campo1  Tipo_dato  Not Null,
 Campo2 Tipo_dato,
 PRIMARY KEY (Campo3));

This would create a table to us with 3 fields of which Campo3 is the only value, that is to say, that cannot be sobreescrito.

To eliminate a table we will use:

DROP TABLE Nombre_tabla;

To modify the structure of the table we will use the following syntax:

ALTER TABLE Nombre_tabla
[ADD Nombre_atributo Definition]    //He would Add a new field
[CHANGE AntiguoNombreAtributo NuevoNombreAtributo Definition]    //It would Change a field
[DROP NombreAtributo];    //It would Erase a field

The indexes are a structure of access that the information contained in a table allows to organize. To create an index we would use the following syntax:

ONE BELIEVE [UNIQUE] INDEX NombreIndice
  ON Table (Fields);

Information manipulation

- information insertion

To insert information in the table it is realized by means of the command insert and his syntax is the following one:

INSERT INTO NombreTabla [Campo1, Campo2... CampoN] VALUE (Valor1, Valor2... ValorN);

- Information consultations

For this action we use the command SELECT and the syntax is the following one:

SELECT ([*] / [Attributes]) FROM Tabla/s [WHERE ListaCondiciones] [GROUP BY Stood out] [HAVING ListaCondiciones] [ORDER BY Stood out]

A set of functions exists inside the consultations of information that allow us to obtain information or realize operations with regard to the lines. The functions are:

- Elimination of information

To eliminate information we use the judgment DELETE whose syntax is the following one:

DELETE FROM NombreTabla [WHERE Condition];