I have this 2 two views. I made a view out of them because they have dependencies on other tables. I then created a query joining them together. Two queries separately has over 30k plus data.
Sample Query would be like:
Select main.*, detail.*
FROM main_data as main
INNER JOIN detail_data AS details ON (main.id = detail.main_id)
WHERE main.column_data LIKE '%something%'
This is slow but if I comment out the "detail.*" on the column section with the join being there is returns the data very fast. What is wrong here?
The expected amount of data is only 20 rows. Still takes very long to perform the select. What makes it slow?
I'd like to add that the joined tables on the view are correct. It is joined accordingly. Like I said If queried separately it returns a lot of data in a very short time.
For more details, actually there is a third table here where both table are a child to. I changed it up to something like this. It improves the performance a bit.
Select main.*, detail.*
FROM parent_data AS par
INNER JOIN main_data as main ON (par.id = detail.par_id)
INNER JOIN detail_data AS details ON (par.id = detail.par_id)
WHERE main.column_data LIKE '%something%'
I made a EXPLAIN SELECT on the exact tables and this is there result:
Thank you.
The only reason the query slows down if you include fields in the resultset from detail table is that detail.main_id is indexed, therefore if no fields are selected from detail, then mysql does not have to touch detail table, it is enough to use the index only. If you do include some fields from that table, then simple index lookup will not be enough, mysql will have to open detail table and get the corresponding records from there.
Try using left join cause you need only connected records from right table:
Select main.*, detail.*
FROM main_data as main
LEFT JOIN detail_data AS details
ON (main.id = detail.main_id AND main.column_data LIKE '%something%')
Related
I have these two tables:
Achievement:
Achieves:
Question:
I want to retrieve rows from table Achievement. But, I do not want all the rows, I want the rows that a specific Steam ID has acquired. Let's take STEAM_0:0:46481449 for example, I want to check first the list of IDs that STEAM_0:0:46481449 has acquired (4th column in Achieves table states whether achievement is acquired or not) and then read only those achievements.
I hope that made sense, if not let me know so I can explain a little better.
I know how to do this with two MySQL statements, but can this be done with a single MySQL statement? That would be awesome if so please tell me :D
EDIT: I will add the two queries below
SELECT * FROM Achieves WHERE Achieves.SteamID = 'STEAM_0:0:46481449' AND Achieves.Acquired = 1;
Then after that I do the following query
SELECT * FROM Achievement;
And then through PHP I would check the IDs that I should take and output those. That's why I wanted to get the same result in 1 query since it's more readable and easier.
In sql left join, applying conditions on second table will filter the result when join conditions doesn't matter:
Select * from achievement
left join achieves on (achievement.id=achieves.id)
where achieves.acquired=1 and achieves.SteamID = 'STEAM_0:0:46481449'
Besides,I suggest not using ID in the achieves table as the shared key between two tables. Name it something else.
I don't think a left join makes sense here. There is no case where you don't want to see the Achievement table.
Something like this
SELECT *
FROM Achieves A
JOIN Achievement B on A.ID = B.ID
WHERE A.SteamID = 'STEAM_0:0:46481449'
AND A.Acquired = 1;
I am working in mysql with queries, but I am new to this. I am joining 5 tables where each table has an identifier and one table is the master. Each related table may have more than one associated record to the master table. I am attempting to join these tables but I can't seem to get rid of the duplicated data.
I want all of the related records to be displayed, but I don't want the data in the master table to display for all results in the related tables. I have tried so many different methods but nothing has worked. Currently I have 4 queries that work for the separate tables, but I have not successfully joined them to have the results display the multiple records in the related table but just one record from the master table.
Here are my individual queries that work:
SELECT
GovernmaxAdditionsExtract.AdditionDescr,
GovernmaxAdditionsExtract.BaseArea,
GovernmaxAdditionsExtract.Value
FROM
GovernmaxExtract
INNER JOIN GovernmaxAdditionsExtract
ON GovernmaxExtract.mpropertyNumber = GovernmaxAdditionsExtract.PropertyNumber
WHERE (((GovernmaxExtract.mpropertyNumber)="xxx-xxx-xx-xxx"));
SELECT
GovernmaxExtract.mpropertyNumber,
GovernmaxDwellingExtract.CardNumber,
GovernmaxDwellingExtract.MainBuildingType,
GovernmaxDwellingExtract.BaseArea
FROM
GovernmaxExtract INNER JOIN
GovernmaxDwellingExtract ON GovernmaxExtract.mpropertyNumber = GovernmaxDwellingExtract.PropertyNumber
WHERE (((GovernmaxExtract.mpropertyNumber)="xxx-xxx-xx-xxx"));
Using these sub queries, I tried to put together 2 of the tables, but now I am getting all records back and it is not reading my input parameter:
SELECT GE.mpropertynumber
FROM
GovernmaxExtract AS GE,
(SELECT
GovernmaxAdditionsExtract.AdditionDescr,
GovernmaxAdditionsExtract.BaseArea,
GovernmaxAdditionsExtract.Value
FROM GovernmaxExtract INNER JOIN
GovernmaxAdditionsExtract ON
governmaxextract.mpropertyNumber = GovernmaxAdditionsExtract.PropertyNumber) AS AE
WHERE GE.mpropertynumber = 'xxx-xxx-xx-xxx'
I tried nested queries, lots of different joins, and I am just not able to wrap my head around this. I am pretty sure I want to do a nested query since I want the main data from the Governmax table to display once with the main data and all records with all info for the associated tables. Maybe I am going about it all wrong.
Our original code was:
SELECT
ge.*,
gde.*,
gfe.*,
gae.*,
goie.*
FROM governmaxextract AS ge
LEFT JOIN governmaxdwellingextract AS gde
ON ge.mpropertyNumber = gde.PropertyNumber
LEFT JOIN governmaxfeaturesextract AS gfe
ON gde.PropertyNumber = gfe.PropertyNumber
LEFT JOIN governmaxadditionsextract AS gae
ON gde.PropertyNumber = gae.PropertyNumber
RIGHT JOIN governmaxotherimprovementsextract AS goie
ON gde.PropertyNumber = goie.PropertyNumber
WHERE ge.mpropertyNumber = '$codeword'
ORDER BY goie.CardNumber
But this gives multiple rows from the master table for each record in the associated tables. I thought about concatenate, but I need the data from the associated tables to be displayed individually. Not sure what to try next. Any help is much appreciated.
Sorry, and there is no way to do that like you want. JOIN's can't do that.
I suggest to keep solution with separate queries.
Btw - You could play with UNION operator,
http://en.wikipedia.org/wiki/Union_(SQL)#UNION_operator
P.s.
You could extract main data separately, then extract data from related tables at once using UNION. With UNIOM it will give one result row per each row in related table.
In order to join an two of the Detail tables together without generating duplicate rows, you will have to perform the following operation on each one:
Group on the foreign key to the Master table, and aggregate all other columns being projected onto the join.
Numeric columns are commonly aggregated with SUM(), COUNT(), MAX(), and MIN(). MAX() and MIN() are also applicable to character data. A PIVOT operation is also sometimes useful as an aggregation operator for this type of circumstance.
Once you have two of the Detail tables grouped and aggregated in this way, they will join without duplicates. Additional Detail tables can be added to the join by first grouping and aggregating them also, in the same fashion.
I have the following tables.
Articles table
a_id INT primary unique
name VARCHAR
Description VARCHAR
c_id INT
Category table
id INT
cat_name VARCHAR
For now I simply use
SELECT a_id,name,Description,cat_name FROM Articles LEFT JOIN Category ON Articles.a_id=Category.id WHERE c_id={$id}
This gives me all articles which belong to a certain category along with category name.
Each article is having only one category.
AND I use a sub category in a similar way(I have another table named sub_cat).But every article doesn't necessary have a sub category.It may belong to multiple categories instead.
I now think of tagging an article with more than one category just like the questions at stackoverflow are tagged(eg: with multiple tags like PHP,MYSQL,SQL etc).AND later I have to display(filter) all article with certain tags(eg: tagged with php,php +MySQL) and I also have to display the tags along with the article name,Description.
Can anyone help me redesign the database?(I am using php + MySQL at back-end)
Create a new table:
CREATE TABLE ArticleCategories(
A_ID INT,
C_ID INT,
Constraint PK_ArticleCategories Primary Key (Article_ID, Category_ID)
)
(this is the SQL server syntax, may be slightly different for MySQL)
This is called a "Junction Table" or a "Mapping Table" and it is how you express Many-to-Many relationships in SQL. So, whenever you want to add a Category to an Article, just INSERT a row into this table with the IDs of the Article and the Category.
For instance, you can initialize it like this:
INSERT Into ArticleCategories(A_ID,C_ID)
SELECT A_ID,C_ID From Articles
Now you can remove c_id from your Articles table.
To get back all of the Categories for a single Article, you would do use a query like this:
SELECT a_id,name,Description,cat_name
FROM Articles
LEFT JOIN ArticleCategories ON Articles.a_id=ArticleCategories.a_id
INNER JOIN Category ON ArticleCategories.c_id=Category.id
WHERE Articles.a_id={$a_id}
Alternatively, to return all articles that have a category LIKE a certain string:
SELECT a_id,name,Description
FROM Articles
WHERE EXISTS( Select *
From ArticleCategories
INNER JOIN Category ON ArticleCategories.c_id=Category.id
WHERE Articles.a_id=ArticleCategories.a_id
AND Category.cat_name LIKE '%'+{$match}+'%'
)
(You may have to adjust the last line, as I am not sure how string parameters are passed MySQL+PHP.)
Ok RBarryYoung you asked me about an reference/analyse you get one
This reference / analyse is based off the documention / source code analyse off the MySQL server
INSERT Into ArticleCategories(A_ID,C_ID)
SELECT A_ID,C_ID From Articles
On an large Articles table with many rows this copy will push one core off the CPU to 100% load and will create a disk based temporary table what will slow down the complete MySQL performance because the disk will be stress out with that copy.
If this is a one time process this is not that bad but do the math if you run this every time..
SELECT a_id,name,Description
FROM Articles
WHERE EXISTS( Select *
From ArticleCategories
INNER JOIN Category ON ArticleCategories.c_id=Category.id
WHERE Articles.a_id=ArticleCategories.a_id
AND Category.cat_name LIKE '%'+{$match}+'%'
)
Note dont take the Execution Times on sqlfriddle for real its an busy server and the times vary alot to make a good statement but look to what View Execution Plan has to say
see http://sqlfiddle.com/#!2/48817/21 for demo
Both querys always trigger an complete table scan on table Articles and two DEPENDENT SUBQUERYS thats not good if you have an large Articles table with many records.
This means the performance depends on the number of Articles rows even when you want only the articles that are in the category.
Select *
From ArticleCategories
INNER JOIN Category ON ArticleCategories.c_id=Category.id
WHERE Articles.a_id=ArticleCategories.a_id
AND Category.cat_name LIKE '%'+{$match}+'%'
This query is the inner subquery but when you try to run it, MySQL cant run because it depends on a value of the Articles table so this is correlated subquery. a subquery type that will be evaluated once for each row processed by the outer query. not good indeed
There are more ways off rewriting RBarryYoung query i will show one.
The INNER JOIN way is much more efficent even with the LIKE operator
Note ive made an habbit out off it that i start with the table with the lowest number off records and work my way up if you start with the table Articles the executing will be the same if the MySQL optimizer chooses the right plan..
SELECT
Articles.a_id
, Articles.name
, Articles.description
FROM
Category
INNER JOIN
ArticleCategories
ON
Category.id = ArticleCategories.c_id
INNER JOIN
Articles
ON
ArticleCategories.a_id = Articles.a_id
WHERE
cat_name LIKE '%php%';
;
see http://sqlfiddle.com/#!2/43451/23 for demo Note that this look worse because it looks like more rows needs to be checkt
Note if the Article table has low number off records RBarryYoung EXIST way and INNER JOIN way will perform more or less the same based on executing times and more proof the INNER JOIN way scales better when the record count become larger
http://sqlfiddle.com/#!2/c11f3/1 EXISTS oeps more Articles records needs to be checked now (even when they are not linked with the ArticleCategories table) so the query is less efficient now
http://sqlfiddle.com/#!2/7aa74/8 INNER JOIN same explain plan as the first demo
Extra notes about scaling it becomes even more worse when you also want to ORDER BY or GROUP BY the NOT EXIST way has an bigger chance it will create an disk based temporary table that will kill MySQL performance
Lets also analyse the LIKE '%php%' vs = 'php' for the EXIST way and INNER JOIN way
the EXIST way
http://sqlfiddle.com/#!2/48817/21 / http://sqlfiddle.com/#!2/c11f3/1 (more Articles) the explain tells me both patterns are more or less the same but 'php' should be little faster because off the const type vs ref in the TYPE column but LIKE %php% will use more CPU because an string compare algoritme needs to run.
the INNER JOIN way
http://sqlfiddle.com/#!2/43451/23 / http://sqlfiddle.com/#!2/7aa74/8 (more Articles) the explain tell me the LIKE '%php%' should be slower because 3 more rows need to be analysed but not shocking slower in this case (you can see the index is not really used on the best way).
RBarryYoung way works but doenst keep performance atleast not on a MySQL server
see http://sqlfiddle.com/#!2/b2bd9/1 or http://sqlfiddle.com/#!2/34ea7/1
for examples that will scale on large tables with lots of records this is what the topic starter needs
I'm trying to query my database for unused listId's but can't quite seem to get the query syntax correct. Here is what I've tried:
SELECT DISTINCT pkListId FROM tblList
INNER JOIN InUseLists ON
tblList.pkListId NOT LIKE InUseLists.fkListId
Where tblList holds all List data, and InUseLists is a view holding all distinct listId's from my relational table.
Currently my tblList holds listId 1-9
my relational table has fkListId 1,8,9 (used more than once)
So my view gets distinct values from the relational table - 1,8,9.
What is wrong with my query syntax?
It sounds like you want a left join (which can succeed whether or not it finds a match in the "right" table), and then to select those rows where the join, in fact, failed to work.
Something like:
SELECT DISTINCT pkListId FROM tblList
LEFT JOIN InUseLists ON
tblList.pkListId LIKE InUseLists.fkListId
WHERE InUseLists.fkListId is null
(If LIKE is the right operator here. Most joins use a simple equality check)
If this still isn't right, it might be better if you edited your question to include the sample data and expected results in a tabular form. At the moment, I'm still not sure what the contents of your tables are, and what you're aiming for.
Try:
SELECT DISTINCT tblList.pkListId, FROM tblList, InUseLists WHERE
tblList.pkListId NOT IN(InUseLists.fkListId)
I have a SELECT query that returns the response based on an unique ID, so I always get just one row.
I thought that I could save my machine an extra SELECT query if I simply added the prices table to the result, and read them to memory later on.
Would that be a good approach or am I missing something ?
(I tried it out and seems to get the job done)
SELECT *
FROM subscriptions
LEFT JOIN prices ON 1=1
WHERE subscriptions.ID = 100
edit: The prices table has no ID. I just need to get the complete table, I used to have a different SELECT just for that
This looks like a terrible idea... you should join the subscriptions table to the prices table using the foreign key that you (supposedly/should) have.
Assuming your prices table has a subscription ID column then your query should look something like this:
SELECT *
FROM subscriptions LEFT JOIN prices ON subscriptions.ID=prices.ID
WHERE subscriptions.ID=100
What this will do is produce a cartesian join - not too bad since you're limiting the 'subscriptions' side of things to a single record, but will still produce as many rows as there's records in the price side. Where this gets bad is when you've got multiple rows on both sides. Then you get n x m results - think of how big the result set would be if you had 50,000 subscriptions joined against 1000 prices: 50,000 x 1,000 = 50 million result rows.
First off, this approach is going to be much less clear what you're doing than two SELECT statements unless there is an actual relation between the tables. Second, it's probably going to be slower, because you're transferring much more data (each row of prices additionally gets all the fields from subscriptions copied).
If subscriptions and prices are related, you want to change that ON condition to use the relation, so you're only pulling the data you need.
SELECT *
FROM subscriptions s LEFT JOIN prices p ON (s.subscription_id = p.subscription_id)
WHERE s.subscription_id = 100
One thing you definitely don't want to do is this:
SELECT *
FROM subscriptions s LEFT JOIN prices p ON (1=1)
as that'd pull the full Cartesian product. Once your tables get sufficiently large, that will run you out of temporary table space.
why your condition have 1=1 ?
I thing that is's must something like this:
SELECT s.*,p.*
FROM subscriptions as s
LEFT JOIN prices as p ON p.product_id=s.product_id
WHERE s.ID = 100
show me your full fields of tables subscriptions and prices to help for you
This?
SELECT *
FROM subscriptions, prices
WHERE subscriptions.ID = 100
You'll get horrible results like this, but it seems this is what you wanted.
The table with less rows will have its rows repeating. Again, this is not a good practice.
Use two SELECTs.
This is a cross join http://en.wikipedia.org/wiki/Join_(SQL)#Cross_join
which means your resultset will contain as many rows as you have in the prices table.
So I guess it is not a good idea