I have this discipline on Uni (over internet) and they asked to build a SELECT with JOIN.
As I have some knowledge about JOIN I tried to build the query without checking the apostille, but after I checked I saw that they are teaching somehow different.
Is it ok to do both ways or is there a "newer" version that I should always use?
The discipline is about Postgresql and I'm used to use MySQL.
Query that I'm used to:
SELECT Cliente.nome, Endereco.rua, Endereco.nro, Endereco.complement
FROM Cliente
JOIN Endereco
ON Endereco.Cod_end = Cliente.Cod_end
JOIN Pedido
ON Pedido.Cod_Cliente = Cliente.Codigo
WHERE Pedido.data = “02/01/16”;
Query that is in the apostille:
SELECT Cliente.nome, Endereco.rua, Endereco.nro, Endereco.complement
FROM Cliente, Endereco, Pedido
Where Endereco.Cod_end = Cliente.Cod_end
AND Pedido.Cod_Cliente = Cliente.Codigo
AND Pedido.data = “02/01/16”;
Related
I am learning SQL and when doing some exercises this question showed up to me.
In matter of Multi-table consults I see sometimes that I can use Where clause instead of inner join, but Í try to use join because is the topic im trying to learn now. In this example I wrote this:
select p.nombre from pokemon p join pokemon_forma_evolucion pfe
on p.numero_pokedex = pfe.numero_pokedex
join forma_evolucion fo
on pfe.id_forma_evolucion = fo.id_forma_evolucion
join tipo_evolucion t
on t.tipo_evolucion = fo.tipo_evolucion
where lower(t.tipo_evolucion) = 'intercambio';
but it shows nothing. ( 0 results )
in the Exercises the correct answer by the blogger is this one and works fine showing 4 results :
select p.nombre
from pokemon p, pokemon_forma_evolucion pfe,
forma_evolucion fe, tipo_evolucion te
where p.numero_pokedex = pfe.numero_pokedex
and pfe.id_forma_evolucion = fe.id_forma_evolucion
and fe.tipo_evolucion = te.id_tipo_evolucion
and lower(te.tipo_evolucion) = 'intercambio';
I would like to know why mine is not working and how should I use the JOIN command properly.
Link of the Exercises blog with DER and access to entire "pokemon" SQL database: https://www.discoduroderoer.es/ejercicios-propuestos-y-resueltos-consultas-sql-bd-pokemon/
Thanks for the help. I am new on posting in this community but it is not the first time I used and enjoyed it.
Thanks for all
the where and join should word fine. the problem is that you are joining the table "tipo_evolucion" ON the wrong field
fild Tipo_Evolucion in table FORMA-EVOLUCION is numeric (this is the foreing key). Fild Tipo_Evolucion in table TIPO_EVOLUCION is varchar2 (this is not the primary key)
the primary key in TIPO_EVOLUCION IS id_tipo_evolucion
So your inner join should be
JOIN tipo_evolucion t ON t.id_tipo_evolucion = fo.tipo_evolucion
the query therefore is:
SELECT p.nombre
FROM pokemon p
JOIN pokemon_forma_evolucion pfe ON p.numero_pokedex = pfe.numero_pokedex
JOIN forma_evolucion fo ON pfe.id_forma_evolucion = fo.id_forma_evolucion
JOIN tipo_evolucion t ON t.id_tipo_evolucion = fo.tipo_evolucion
WHERE LOWER(t.tipo_evolucion) = 'intercambio';
I have RATE and BRANCH_CURRE table. I want to perform left join operation (joining branch to rate) in Doctrine Query Language (DQL).
My SQL Query is:
SELECT r.id rid
,r.TIME rtime
,r.rate_candidate
,r.exchange_rate
,r.branch
,r.STATUS ratestatus
,bc.currency
,bc.scale bcscale
,bc.STATUS bcstatus
FROM rate r
LEFT JOIN branch_currency bc ON (
r.branch = bc.branch
AND (
r.from_currency = bc.currency
OR r.to_currency = bc.currency
)
)
WHERE r.STATUS = 1
AND bc.STATUS = 1;
To be more specific, I have two questions here
How to select some specific columns from both the tables.
How to give the multiple ON conditions while joining tables.
So Please show the DQL query using queryBuilder(). Thanx in advance!!!
I suggest to add the additional conditions into a where condition.
Other than that I highly recommend to read the documentation regarding the Doctrine QueryBuilder etc. because you're question does not show that you have any experience with Doctrine at all. Just throwing a MySQL query without any personal effort at us is not a nice and fair way.
This is not tested but should give you some guidance.
$qb = $this->_em->createQueryBuilder();
$qb->select('r.branch, bc.exchange_rate');
$qb->from('rate', 'r');
$qb->leftJoin('r.branch', 'bc');
$qb->where($qb->expr()->orX('r.from_currency=bc.currency','r.to_currency = bc.currency));
So, this query is currently used in a webshop to retrieve technical data about articles.
It has served its purpose fine except the amount of products shown have increased lately resulting in unacceptable long loading times for some categories.
For one of the worst pages this (and some other queries) get requested about 80 times.
I only recently learned that MySQL does not optimize sub-queries that don't have a depending parameter to only run once.
So if someone could help me with one of the queries and explain how you can replace the in's and exists's to joins, i will probably be able to change the other ones myself.
select distinct criteria.cri_id, des_texts.tex_text, article_criteria.acr_value, article_criteria.acr_kv_des_id
from article_criteria, designations, des_texts, criteria, articles
where article_criteria.acr_cri_id = criteria.cri_id
and article_criteria.acr_art_id = articles.art_id
and articles.art_deliverystatus = 1
and criteria.cri_des_id = designations.des_id
and designations.des_lng_id = 9
and designations.des_tex_id = des_texts.tex_id
and criteria.cri_id = 328
and article_criteria.acr_art_id IN (Select distinct link_art.la_art_id
from link_art, link_la_typ
where link_art.la_id = link_la_typ.lat_la_id
and link_la_typ.lat_typ_id = 17484
and link_art.la_ga_id IN (Select distinct link_ga_str.lgs_ga_id
from link_ga_str, search_tree
where link_ga_str.lgs_str_id = search_tree.str_id
and search_tree.str_type = 1
and search_tree.str_id = 10132
and EXISTS (Select *
from link_la_typ
where link_la_typ.lat_typ_id = 17484
and link_ga_str.lgs_ga_id = link_la_typ.lat_ga_id)))
order by article_criteria.acr_value
I think this one is the main badguy with sub-sub-sub-queries
I just noticed i can remove the last exist and still get the same results but with no increase in speed, not part of the question though ;) i'll figure out myself whether i still need that part.
Any help or pointers are appreciated, if i left out some useful information tell me as well.
I think this is equivalent:
SELECT DISTINCT c.cri_id, dt.tex_text, ac.acr_value, ac.acr_kv_des_id
FROM article_criteria AS ac
JOIN criteria AS c ON ac.acr_cri_id = c.cri_id
JOIN articles AS a ON ac.acr_art_id = a.art_id
JOIN designations AS d ON c.cri_des_id = d.des_id
JOIN des_texts AS dt ON dt.tex_id = d.des_tex_id
JOIN (SELECT distinct la.la_art_id
FROM link_art AS la
JOIN link_la_typ AS llt ON la.la_id = llt.lat_la_id
JOIN (SELECT DISTINCT lgs.lgs_ga_id
FROM link_ga_str AS lgs
JOIN search_tree AS st ON lgs.lgs_str_id = st.str_id
JOIN link_la_typ AS llt ON lgs.lgs_ga_id = llt.lat_ga_id
WHERE st.str_type = 1
AND st.str_id = 10132
AND llt.lat_typ_id = 17484) AS lgs
ON la.la_ga_id = lgs.lgs_ga_id
WHERE llt.lat_typ_id = 17484) AS la
ON ac.acr_art_id = la.la_art_id
WHERE a.art_deliverystatus = 1
AND d.des_lng_id = 9
AND c.cri_id = 328
ORDER BY ac.acr_value
All the IN <subquery> clauses can be replaced with JOIN <subquery>, where you then JOIN on the column being tested equaling the column returned by the subquery. And the EXISTS test is converted to a join with the table, moving the comparison in the subquery's WHERE clause into the ON clause of the JOIN.
It's probably possible to flatten the whole thing, instead of joining with subqueries. But I suspect performance will be poor, because this won't reduce the temporary tables using DISTINCT. So you'll get combinatorial explosion in the resulting cross product, which will then have to be reduced at the end with the DISTINCT at the top.
I've converted all the implicit joins to ANSI JOIN clauses, to make the structure clearer, and added table aliases to make things more readable.
In general, you can convert a FROM tab1 WHERE ... val IN (SELECT blah) to a join like this.
FROM tab1
JOIN (
SELECT tab1_id
FROM tab2
JOIN tab3 ON whatever = whatever
WHERE whatever
) AS sub1 ON tab1.id = sub1.tab1_id
The JOIN (an inner join) will drop the rows that don't match the ON condition from your query.
If your tab1_id values can come up duplicate from your inner query, use SELECT DISTINCT. But don't use SELECT DISTINCT unless you need to; it is costly to evaluate.
I am trying to join the following tables with the following code, but I can't join the last columns.
Table:magazine
id_mag **mag_name** id_freq
Table:frequency
id_freq **freq_name**
Table:copy
id_mag **id_copy** **copy_date** copy_price copy_page_number
Table:article
id_art **art_name** **art_page_number**
Table:copy_art
id_mag **id_copy** id_art article_page_num
I want to show a table with the following columns. The columns in the tables magazine, frequency, copy, article & copy_art that have ** ** are the ones I am interested in to be showed:
mag_name freq_name id_copy copy_date art_name art_page_number
I got the following table with this code:
SELECT * FROM magazine
JOIN frequency ON magazine.id_freq = frequency.id_freq
JOIN copy_art ON revista.id_mag=copy_art.id_mag
JOIN article ON copy_art.id_art=article.id_art
JOIN copy ON copy_art.id_copy=copy.id_copy;
Here is the translation for the name of each column that appears in the image:
id_rev = id_mag
nom_rev = mag_name
id_frec = id_freq
nom_frec = freq_name
id_rev = id_mag
id_ejem = id_copy
id_art = id_art
num_pag = article_page_num
nom_art = art_name
num_pag_art = art_page_number
fecha_ejem = copy_date
precio = copy_price
My doubt is the following:
What should I do in order to have the table with?
mag_name freq_name id_copy copy_date art_name article_page_num
Thanks a lot for your kindly support!
If you only want a few columns in the output, then you have to list which columns you do want. The key structure of the data is unclear (meaning it isn't clear which columns are the primary keys of each table); you have the id_mag and id_copy columns both appearing in copy and copy_art and it isn't entirely clear whether they're a composite key or id_copy is sufficient. Given that we don't have that information, we'll have to take your SELECT statement and its joins as gospel, but I'm not convinced that's correct.
You wrote:
SELECT *
FROM magazine
JOIN frequency ON magazine.id_freq = frequency.id_freq
JOIN copy_art ON revista.id_mag=copy_art.id_mag
JOIN article ON copy_art.id_art=article.id_art
JOIN copy ON copy_art.id_copy=copy.id_copy;
This collects all the columns from all the tables mentioned, which is wasteful. So, you need to specify which columns you do want:
SELECT m.mag_name, f.freq_name, c.id_copy, c.copy_date, a.art_name, a.art_page_number
FROM magazine AS m
JOIN frequency AS f ON m.id_freq = f.id_freq
JOIN copy_art AS y ON m.id_mag = y.id_mag
JOIN article AS a ON y.id_art = a.id_art
JOIN copy AS c ON y.id_copy = c.id_copy;
I'm not entirely sure that you need the copy_art table in the query, but I'm assuming you know your data better than I do.
You have to make sure that one of the first tables has got a foreign key for the articulo table to join that as well.
If you add that (For example in the revista table), you can make a JOIN over all tables with something like this:
SELECT * FROM revista
JOIN frecuencia ON revista.id_frec = frecuencia.id_frec
JOIN ejemplar ON revista.id_rev = ejemplar.id_rev
JOIN articulo ON revista.id_art = articulo.id_art;
See this fiddle for an example (I query * here, you can change that to just the columns that you need).
I have written a Query,
SELECT dbo.boat.boatno, dbo.boat.boattype, dbo.staff.staffFirstName, dbo.staff.staffLastName,
dbo.branch.branchAddress
FROM dbo.boat INNER JOIN
dbo.BoatOwner ON dbo.boat.OwnerNo = dbo.BoatOwner.OwnerNo INNER JOIN
dbo.branch ON dbo.boat.BranchNo = dbo.branch.branchno INNER JOIN
dbo.staff ON dbo.branch.branchno = dbo.staff.Branchno
WHERE (dbo.branch.branchAddress LIKE '%LONDON%')
But It doesn't work in MYSQL QUERY
How can i convert this into MYSQL QUERY?
You need to know correct table names for MySQL. Assuming a similar structure, I might try:
SELECT b.boatno, b.boattype, s.staffFirstName, s.staffLastName, br.branchAddress
FROM boat b INNER JOIN
BoatOwner bo
ON b.OwnerNo = bo.OwnerNo INNER JOIN
branch br
ON b.BranchNo = br.branchno INNER JOIN
staff s
ON br.branchno = s.Branchno
WHERE br.branchAddress LIKE '%LONDON%';
MySQL does not use the three-part naming that SQL Server does. There is no "schema" in the middle of the name. The additional periods in the column names are probably one source of confusion. Using table aliases should work in both databases and makes the code more readable.
Just a guess from general principles, but perhaps the simpler
SELECT A.boatno, A.boattype, D.staffFirstName, D.staffLastName, C.branchAddress
FROM dbo.boat A, dbo.BoatOwner B, dbo.branch C, dbo.staff D
WHERE B.OwnerNo = A.OwnerNo AND C.branchno = A.BranchNo AND D.Branchno = C.branchno
AND C.branchAddress LIKE '%LONDON%'
may work.
To begin, make sure also that you can SELECT from dbo.boat, dbo.BoatOwner, dbo.branch and dbo.staff using your PHPmyAdmin environment. Sometimes the simple things trip us up...
SELECT b.boatno, b.boattype, s.staffFirstName, s.staffLastName, br.branchAddress
FROM boat b INNER JOIN
BoatOwner bo
ON b.OwnerNo = bo.OwnerNo INNER JOIN
branch br
ON b.BranchNo = br.branchno INNER JOIN
staff s
ON br.branchno = s.Branchno
WHERE br.branchAddress LIKE '%LONDON%';
GROUP BY b.boatno
Isn't that enought?