Search in different tables knowing which came the result

2

I am trying to search for a term in 4 different tables in MySQL, using like , but I need to retrieve the id of each one and identify which table came to do the listing and direct with link.

This is a search system where the results should have a link to the corresponding page with id of each result.

I've tried to use 4 selects and union , but I did not succeed.

Last attempt was made:

("SELECT * FROM web_tv WHERE (titulo LIKE '%".$busca."%' OR (texto '%".$busca."%')) UNION SELECT * FROM agenda WHERE (titulo LIKE '%".$busca."%' OR (texto '%".$busca."%')) UNION SELECT * FROM blog WHERE (titulo LIKE '%".$busca."%' OR (texto '%".$busca."%')) UNION SELECT * FROM osorio WHERE (titulo LIKE '%".$busca."%' OR (texto '%".$busca."%'")
    
asked by anonymous 04.11.2016 / 16:22

1 answer

5

General use of UNION with condition:

SELECT campo1, campo2 FROM tabela1 WHERE ...
UNION
SELECT campo1, campo2 FROM tabela2 WHERE ...
UNION
SELECT campo1, campo2 FROM tabela3 WHERE ...
UNION
SELECT campo1, campo2 FROM tabela4 WHERE ...

Or:

SELECT * FROM (
    SELECT campo1, campo2 FROM tabela1 
    UNION
    SELECT campo1, campo2 FROM tabela2 
    UNION
    SELECT campo1, campo2 FROM tabela3 
    UNION
    SELECT campo1, campo2 FROM tabela4 
) todos
WHERE condicao


Applying to your case and differentiating the tables:

Usually in SQL you do not have to return only fields, you can use expressions involving more than one field, or simply not use fields in any of the columns. And here's what we're going to do:

SELECT 'web_tv' AS tabela, campo1, campo2 
       ^^^^^^^^^^^^^^^^^^

This select will always return a field named tabela with content webtv , to know where the information came from, thus:

SELECT 'web_tv' AS tabela, campo1, campo2 FROM web_tv WHERE ...condicoes...
UNION
SELECT 'agenda' AS tabela, campo1, campo2 FROM agenda WHERE ...condicoes...
UNION
SELECT 'blog'   AS tabela, campo1, campo2 FROM blog   WHERE ...condicoes...
UNION
SELECT 'osorio' AS tabela, campo1, campo2 FROM osorio WHERE ...condicoes...

I recommend using only the fields that are in fact required for the search, instead of * , whenever possible. In some situations * is more practical, but generally specifying the columns is almost always more secure.

If you really want to use * , you can do this:

SELECT 'web_tv' AS tabela, * FROM web_tv WHERE ...condicoes...
UNION
SELECT 'agenda' AS tabela, * FROM agenda WHERE ...condicoes...
...

But it will only give you a headache when you restructure any of them, plus it will probably be returning data you will not use.

The important thing is to understand that we have created a literal column with the names of the original table so you know which result came from where.

If you want to simplify, you can use a numeric value:

SELECT 1 AS tabela, * FROM web_tv WHERE ...condicoes...


Tip of simplification

This here:

WHERE titulo LIKE '%".$busca."%' OR texto LIKE '%".$busca."%'

It can be simplified this way:

WHERE concat_ws( ' ', titulo, texto ) LIKE '%".$busca."%'

In the case of two fields does not change much, but if you have more fields, can make your life easier.


Alternative syntax

First of all, it's important to say that when you use this way, UNION will probably generate a temporary result set and then apply WHERE , which is not very performative . But, as in your case it is a question of LIKE with % on both sides, it ends up giving it anyway, because in any case the records will be read one by one (in all cases).

SELECT * FROM (
    SELECT 'web_tv' AS tabela, campo1, campo2 FROM web_tv
    UNION
    SELECT 'agenda' AS tabela, campo1, campo2 FROM agenda
    UNION
    SELECT 'blog'   AS tabela, campo1, campo2 FROM blog
    UNION
    SELECT 'osorio' AS tabela, campo1, campo2 FROM osorio
) todos
WHERE todos.campo1 LIKE '%".$busca."%' OR todos.campo2 ....
ORDER BY todos.campo1
    
04.11.2016 / 17:28