Concatenate two fields

The error is in the quotes should give a space

SELECT documento, concat(nombres, ' ', apellidos) as datos, nacimiento FROM jugador

  

The CONCAT what it does is concatenate two or more columns of a table,   that is, visualize the data of 2 or more columns in one, as in   your case has the column Nombre and Apellido and the CONCAT   allows you to visualize both in a single field, you can add words in   the fields to concatenate or blank spaces as is your case.

Keep in mind that CONCAT has a serious problem with the values NULL :

  

CONCAT() returns NULL if any argument is NULL .

     

CONCAT() returns NULL if any argument is NULL .

Therefore, in MySQL you must use CONCAT_WS if values that you are going to concatenate can have values NULL .

  

CONCAT_WS() does not skip empty strings. However, it does skip any   % co_of% values after the separator argument.

Also, in case you have to concatenate multiple columns and the separator is always the same, the code is cleaner.

For example:

If using NULL you have to write this:

SELECT 
CONCAT(col1, ' ', col2, ' ', col3, ' ', col4, ' ', col5, ... col999-y-999separadores) 
as datos;

With CONCAT you put the tab only once , at the beginning, and you're done:

SELECT 
CONCAT_WS(' ', col1, col2, col3, col4, col5, ... col999) 
as  datos;

It is important to pay attention to this

Let's see a demo of what happens if there are nulls between the values you want to concatenate. With CONCAT_WS you're never going to see Santiago because his last name is CONCAT !!! :)

CREATE TABLE IF NOT EXISTS persona (
    id         SERIAL,
    nombre     VARCHAR(50),
    apellido   VARCHAR(50)
);

INSERT INTO persona (nombre, apellido) VALUES ('Pedro','Pérez');
INSERT INTO persona (nombre, apellido) VALUES ('Santiago',NULL);
INSERT INTO persona (nombre, apellido) VALUES ('Juan',' ');

-- Tratamiento de NULL con CONCAT_WS
SELECT CONCAT_WS(' ',nombre, apellido) datos FROM persona;

-- Tratamiento de NULL con CONCAT ... ¡terrible!
SELECT CONCAT(nombre, ' ',apellido) datos FROM persona;

NULL

    datos
1   Pedro Pérez
2   Santiago
3   Juan  

Resultado con CONCAT_WS:

    datos
1   Pedro Pérez
2   NULL
3   Juan  

  

PS: For more details you can consult this question:

     

• Use CONCAT or CONCAT_WS in MySQL?
  

You are not placing the space, simply a string without text, you should try this:

SELECT documento, concat(nombres, ' ', apellidos) as datos, nacimiento FROM jugador
                                   ^ Aquí

or even like this:

SELECT documento, datos = nombres + ' ' + apellidos, nacimiento FROM jugador

CONCAT simply joins texts, one after the other, of those you pass as parameters separated by commas ( , ), you can join in a single text all you want; for the case before joining the two VARCHAR you want you must add, between both, the blank space that is what was missing from your original query.

The second case that I put you does practically the same, concatenate but "adding" the text to the right of + to the text that is on the left being technically different from CONCAT that creates a new text but finally gets the same result.

Although in the tags you indicate that it is for MySql, in case someone comes to this question interested in other languages, in other languages (remember now for example PostgreSQL or Multibase) the contatenación is done with || .

Your example would result in this way:

SELECT documento, nombres || ' ' || apellidos as datos, nacimiento FROM jugador