I'm trying to get this to work. When I run the SELECT on the whole dataset I know that the record with cust_number shows up in position 6 (When Using ORDER BY) but this code returns position 37327 which is it's non ordered by position.
SELECT
x.position,
x.cust_number,
x.company,
x.surname,
x.first_name,
x.title
FROM
(SELECT
#rownum:=#rownum + 1 AS position,
c.cust_number,
company,
surname,
first_name,
title
FROM
1_customer_records c
LEFT JOIN addresses a ON c.fk_addresses_id = a.id
JOIN (SELECT #rownum:=0) r
ORDER BY a.company , c.surname , c.first_name , c.title) x
WHERE
x.cust_number = 43246;
Here is another approach using a temp table
CREATE TEMPORARY TABLE row_calc (id INT AUTO_INCREMENT, fk INT NULL, PRIMARY KEY (id)) ENGINE=MEMORY;
INSERT INTO row_calc(fk)
SELECT
cust_number
FROM
1_customer_records c
LEFT JOIN
addresses a ON c.fk_addresses_id = a.id
ORDER BY company,surname,first_name,title;
SELECT
id
FROM
row_calc
WHERE
fk = 43246 LIMIT 1;
DROP TABLE row_calc;
Related
I have the table contacts which contains duplicate records:
id name is_contacted created_at
I need to delete duplicates, but keep the first record(among the duplicates for each name) where is_contacted=1.
If among the record duplicates there are no records where is_contacted=1, just keep the first one.
This is what I have so far:
DELETE c1 FROM contacts c1
INNER JOIN contacts c2
WHERE
c1.id > c2.id AND
c1.name = c2.name;
Assuming that is_contacted's data type is BOOLEAN and id is the primary key of the table and this is the column that defines the order and which row should be considered first, use ROW_NUMBER window function to rank the rows of each name:
WITH cte AS (
SELECT *, ROW_NUMBER() OVER (PARTITION BY name ORDER BY is_contacted DESC, id) rn
FROM contacts
)
DELETE t
FROM contacts t INNER JOIN cte c
ON c.id = t.id
WHERE c.rn > 1;
ORDER BY is_contacted DESC, id returns the rows with is_contacted = 1 at the top (if they exist).
For versions of MySql prior to 8.0, without support of CTEs and winow functions, use a join of the table to a query that uses aggregation to get the id of the row that you want to keep:
DELETE t
FROM contacts t
INNER JOIN (
SELECT name,
COALESCE(MIN(CASE WHEN is_contacted THEN id END), MIN(id)) id
FROM contacts
GROUP BY name
) c ON c.name = t.name AND c.id <> t.id;
Below query will filter only records what you want.
You didn't mention what is primary key in your table, so I don't know how to join this back 1:1 with your whole table.
But if you are not able to determine primary key, they you can create new table using this query, drop original one and rename it to original one.
SELECT * FROM
(
SELECT *,
ROW_NUMBER(PARTITION BY name ORDER BY CASE WHEN is_contacted = 1 THEN -999999 else is_contacted END ) AS RN_
from contacts
) c
WHERE c.RN_ = 1
First İ use wherehas but then I decided use this way. This way result better than wherehas but It isn't satisfy me. Query response time is a 873ms. So I have 400k+ data in the table.
select count(*) as aggregate
from `orders`
where (`pickup_address_id` in (
select `id`
from `addresses`
where `region_id` = 12)
or `delivery_address_id` in (
select `id`
from `addresses`
where `region_id` = 12)
) and `orders`.`status` = 2
Try this:
select count(distinct o.`id`) as aggregate
from `orders` o
inner join `addresses` a ON a.`id` IN (o.`pickup_address_id`, o.`delivery_address_id`)
AND a.`region_id` = 12
where o.`status` = 2
Alternatively:
SELECT count(distinct id) as aggregate
FROM (
select o.`id`
from `orders` o
inner join `addresses` a ON a.`id` = o.`pickup_address_id`
AND a.`region_id` = 12
where o.`status` = 2
UNION
select o.`id`
from `orders` o
inner join `addresses` a ON a.`id` = o.`delivery_address_id`
AND a.`region_id` = 12
where o.`status` = 2
) t
But I don't know you'll improve much to look through 400K rows in less than a second.
First, you can try to eliminate multiple (twice, to be more precise) same subquery evaluation using a Common Table Expression
WITH CTE(id) AS (
SELECT id
FROM addresses
WHERE region_id = 12
)
This CTE would be evaluated once.
Second, get row count from orders table joined with cte on existence of pickup_address_id and delivery_address_id in cte.
WITH CTE(id) AS (
SELECT id
FROM addresses
WHERE region_id = 12
)
SELECT COUNT (*)
FROM orders
CROSS JOIN CTE ON CTE.id = orders.delivery_address_id
OR CTE.id = orders.pickup_address_id
Finally, add filter by status = 2 and query would be like
WITH CTE(id) AS (
SELECT id
FROM addresses
WHERE region_id = 12
)
SELECT COUNT (*)
FROM orders
CROSS JOIN CTE ON CTE.id = orders.delivery_address_id
OR CTE.id = orders.pickup_address_id
WHERE orders.status = 2
Also you should have the following indexes:
addresses table:
INDEX (region_id)
orders table:
INDEX (pickup_address_id),
INDEX (delivery_address_id),
INDEX (status)
Give it a try.
With empty tables I've got this
Schema (MySQL v8.0)
create table addresses (
id int primary key,
region_id int not null,
index(region_id)
);
create table orders (
id int primary key,
pickup_address_id int,
delivery_address_id int,
status int not null,
index (pickup_address_id),
index (delivery_address_id),
index(status),
foreign key (pickup_address_id) references addresses(id),
foreign key (delivery_address_id) references addresses(id)
);
Query #1
explain with cte(id) as (
select id from addresses where region_id = 12)
select count(*) from orders
cross join cte on cte.id = orders.delivery_address_id
or cte.id = orders.pickup_address_id
where status = 2;
id
select_type
table
partitions
type
possible_keys
key
key_len
ref
rows
filtered
Extra
1
SIMPLE
orders
ref
pickup_address_id,delivery_address_id,status
status
4
const
1
100
1
SIMPLE
addresses
ref
PRIMARY,region_id
region_id
4
const
1
100
Using where; Using index
I have a base query which uses a view which uses another view, like this.
SELECT a,b,c,DEBIT_AMOUNT, CREDIT_AMOUNT FROM MAIN_VIEW WHERE a='foo' AND c='bar';
Here's the schema
create table BASE_TABLE (
id int not null auto_increment,
a varchar(20),
b varchar(20),
c varchar(20),
primary key (id));
create table OTHER_TABLE (
oid int not null auto_increment,
id int not null,
mtype varchar(10),
amount varchar(20),
primary key (oid));
create or replace view `MAIN_VIEW` AS
SELECT BT.a, BT.b, BT.c,SUB_VIEW.DEBIT_AMOUNT, SUB_VIEW.CREDIT_AMOUNT
FROM BASE_TABLE BT
LEFT JOIN SUB_VIEW ON SUB_VIEW.id = BT.id
create or replace view `SUB_VIEW` AS
SELECT BT.id,
( SELECT SUM(O.amount)
FROM OTHER_TABLE O
WHERE O.mtype = 'DR'
AND O.id = BT.id
) AS DEBIT_AMOUNT,
( SELECT SUM(O.amount)
FROM OTHER_TABLE O
WHERE O.mtype = 'CR'
AND O.id = BT.id
) AS CREDIT_AMOUNT
FROM BASE_TABLE BT
My query is permformance is very slow, to speed up query execution, i've modified the MAIN_VIEW like this
since the BASE_TABLE is already available on MAIN_VIEW, i thought fetching DEBIT_AMOUNT and CREDIT_AMOUNT from then and there rather than going into the SUB_VIEW
-- MAIN_VIEW ---
create or replace view `MAIN_VIEW` AS
SELECT BT.a, BT.b, BT.c,
( SELECT SUM(O.amount)
FROM OTHER_TABLE O
WHERE O.mtype = 'DR'
AND O.id = BT.id
) AS DEBIT_AMOUNT,
( SELECT SUM(O.amount)
FROM OTHER_TABLE O
WHERE O.mtype = 'CR'
AND O.id = BT.id
) AS CREDIT_AMOUNT
FROM BASE_TABLE BT
But after this modification, query performance is even worse.. can any one help? I thought subviews are be bad for performance...
You need INDEX(id, mtype) (in either order). This should make the subqueries faster, hence the entire query faster.
Does MySQL support common table expressions? For example in Oracle there's the WITH clause? :
WITH aliasname
AS
( SELECT COUNT(*) FROM table_name )
SELECT COUNT(*) FROM dept,aliasname
SELECT t.name,
t.num
FROM TABLE t
JOIN (SELECT c.id,COUNT(*) 'num1'
FROM TABLE1 c
WHERE c.column = 'a'
GROUP BY c.id) ta1 ON ta1.id = t.id
JOIN (SELECT d.id,COUNT(*) 'num2'
FROM TABLE2 d
WHERE d.column = 'a'
GROUP BY d.id) ta2 ON ta2.id = t.id
One way is to use a subquery:
SELECT COUNT(*)
FROM dept,
(
SELECT COUNT(*)
FROM table_name
) AS aliasname
Note that the , between the two tables will cross join the two tables the same as in your query you posted. IF there is any relation between them you can JOIN them instead.
No, MySQL does not support Common Table Expressions (CTE). So instead of using WITH tablealias as (....), you will have to do a subquery.
For example,
WITH totalcount AS
(select userid, count(*) as tot from logins group by userid)
SELECT a.firstname, a.lastname, b.tot
FROM users a
INNER JOIN
totalcount b
on a.userid = b.userid
can be re-written in MySQL as
SELECT a.firstname, a.lastname, b.totalcount
FROM users a
INNER JOIN
(select userid, count(*) as tot from logins group by userid) b
on a.userid = b.userid
So let's talk about WITH clause .
WITH clause and INNER JOIN otherwise JOIN are a kind of same , but WITH clause gives you much more latitude especially in WHERE clause ;
I am going to make a view that'll get values like count of users , user name and etc.
First (Creating our tables users and inserted_users) :
inserted_users table :
CREATE TABLE users (id BIGINT(10) AUTO INCEREMENT PRIMARY KEY , name VARCHAR(50))
users table :
CREATE TABLE users (id BIGINT(10) AUTO INCEREMENT PRIMARY KEY , name VARCHAR(50) , gender TINYINT(1))
Second (Inserting some values to work with) :
users table :
INSERT INTO users (name,gender) VALUES ('Abolfazl M' , 1)
I don't want to insert into inserted_users by query , but I want to add a TRUGGER which will insert data automatically to users_inserted table before data be inserted into users table.
Third (Creating trigger add_uinserted) :
DELIMITER $$
CREATE TRIGGER IF NOT EXISTS add_uinserted BEFORE INSERT ON users FOR EACH ROW
BEGIN
IF NEW.name <> '' THEN
INSERT INTO users_inserted (name) VALUES (NEW.name);
ELSE
INSERT INTO users (name,gender) VALUES ('Unknown',NEW.gender);
INSERT INTO users_inserted (name) VALUES ('Unknown');
END IF;
END$$
DELIMITER ;
Run the query and the trigger will be created and at last let's create a view to give us result from a query having WITH clause .
CREATE VIEW select_users AS
WITH GetCAll AS (
SELECT u1.id As Uid ,COUNT(u1.name) AS CnAll FROM users u1
)
SELECT u1.name AS NAME,CASE
WHEN s1.gender = 1 THEN "MALE"
WHEN s1.gender = 0 THEN "FEMALE"
ELSE "UNKNOWN"
END AS GENDER,CASE
WHEN u1.id = gca.Uid THEN "INSERTED TO users_inserted"
ELSE "NOT INSERTED TO users_inserted"
END AS INSERTED,gca.CnAll FROM GetCAll AS gca INNER JOIN users u1;
After you query got ran the view will be created and by calling the view select_users the data will be shown
Last step (calling the select_users view) :
SELECT * FROM select_users
Thanks for taking a look at my answer , and that's it !!
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Mysql: Perform of NOT EXISTS. Is it possible to improve permofance?
Is there a better/optimal way to do it. Should I use exists instead of join? Or two separate queries? And what about temporary tables, as I was reading about those but uncertain.
Getting members email from a group. Checking that they have not received a item yet.
SELECT m.email,g.id
FROM group g
LEFT JOIN members m
ON g.mid = m.id
AND g.gid='1'
WHERE NOT EXISTS
( SELECT id
FROM items AS i
WHERE i.mid=m.id
AND i.item_id='5'
)
Here's the same thing written as a JOIN:
SELECT m.email, g.id
From members m
JOIN group g ON g.mid = m.id AND g.gid = '1'
LEFT JOIN items i ON i.mid = m.id AND i.item_id = '5'
WHERE i.id IS NULL
Use the following compound indexes:
group (mid, gid)
items (mid, item_id)
I reversed the LEFT JOIN on members and group because it seems like you're returning members, not groups, and I changed the LEFT JOIN into an INNER JOIN since you only want members from that group.
I think this one might read better:
SELECT m.email, g.id
From members m
JOIN group g ON g.mid = m.id
LEFT JOIN items i ON i.mid = m.id AND i.item_id = 5
WHERE g.gid = 1
AND i.id IS NULL
You might be wondering if we can move the i.item_id = 5 part to the WHERE clause also. You can't because there are no rows where i.id IS NULL and i.item_id = 5. You must do the join first and then eliminate the NULL rows in the WHERE clause.
I don't believe a temporary table is necessary. We'd really only go that route if we can't get acceptable performance.
From your query, we gather your schema looks like this:
group (id INT PK, gid INT, mid INT)
items (id INT PK, item_id INT, mid INT)
members (id INT PK, email VARCHAR)
It looks like your group table is really a "membership" table, which resolves/implements a many-to-many relationship between a group and a person. (That is, a person can be a member of zero, one or more groups; a group can have zero, or or more persons as members.)
You are using a LEFT JOIN between group and members. This will return a row for group (returning group.id) when there are no matching members, with a NULL for members.email (which may be what you want). But if you only want to return email addresses, then this can be changed to an INNER JOIN.
The NOT EXISTS predicate can be replaced with an OUTER JOIN and a test for a NULL value returned from the JOINED table. If the group.gid and/or items.item_id columns are numeric datatype, then you can remove the quotes from around the integer literals in the predicates.
Here is an alternative which will return an equivalent resultset, and may perform better:
SELECT m.email
, g.id
FROM members m
JOIN group g ON g.mid = m.id AND g.gid = 1
LEFT
JOIN items i ON i.mid = m.id AND i.item_id = 5
WHERE i.id IS NULL
ADDENDUM:
TEST CASE (provided in comment on selected answer) demonstrates difference in result set between queries with the predicate items.item_id = 5 in the ON clause and in the WHERE clause. (Moving this predicate to the WHERE clause messes with the anti-join.)
CREATE TABLE `group` (`id` INT PRIMARY KEY, `gid` INT, `mid` INT);
CREATE TABLE `items` (`id` INT PRIMARY KEY, `item_id` INT, `mid` INT);
CREATE TABLE `members` (`id` INT PRIMARY KEY, `email` VARCHAR(40));
INSERT INTO `group` VALUES (1,1,1), (2,1,2);
INSERT INTO `items` VALUES (1,5,1);
INSERT INTO `members` VALUES (1,'one#m.com'),(2,'two#m.com');