Ok, so I have an organization id column named org_id in several databases.
I am writing a search function that will query two of these databases, and look for all org_id's associated with a value in these two tables.
I ONLY want to ultimately have the org_id's that correspond with the values I am querying for in EACH table.
For example:
Say I have an org_id of 3 that is in the tables cult_xref and cat_xref, which are both associated with an organization table, which isn't really relevant for this. I want to ONLY pull those org_id's which are in BOTH tables cult_xref and cat_xref, based on values I put into those tables, say 2 and 6 respectively.
So:
cult_xref
org_id | cult_id
3 | 2
4 | 2
3 | 5
and
cat_xref
org_id | cat_id
3 | 6
3 | 1
7 | 6
I would only want to pull the org_id's that fulfill cult_id['2'] and cat_id['6'] at the SAME TIME.
In SQL, this is called a JOIN.
SELECT org_id
FROM cult_xref INNER JOIN cat_xref USING (org_id)
WHERE (cult_id,cat_id) = (2,6)
For a nice introduction to joins, see A Visual Explanation of SQL Joins
Related
I have three tables:
Users (columns id, dept_id)
Departments (columns id, deptStringName)
Absences (columns id, user_id)
I am trying to figure out Absences per Department. I know I need two inner joins, but at the moment I am confused about how to insert a count in two inner joins using the Laravel Query Builder syntax.
The eventual result could be like:
+-------+---+
| DeptA | 3 |
| DeptF | 7 |
| DeptH | 3 |
| DeptT | 7 |
| DeptZ | 5 |
+-------+---+
EDIT: I don't mind the SQL syntax either.
So basically something like the following should work:
DB::table('departments')
->join('users','users.dept_id','=','departments.id')
->join('absences','users.id','=','absences.user_id')
->select('departments.id','departments.deptStringName', DB::raw("COUNT(*)"))
->groupBy('departments.id','departments.deptStringName')
->get();
Note: When grouping by you should group by the unique values of the row (e.g. the identifier). If your department names are guaranteed to be unique then you can omit selecting and grouping by department.id completely.
I have a table with all my invoice items as packages:
Table: invoice_items
invoice_item_id | package_id | addon_1 | addon_2 | addon_3 | ...
----------------|------------|---------|---------|
1 | 6 | 2 | 5 | 3 |
Then my other table:
Table: addons
addon_id | addon_name | addon_desc |
----------|--------------|--------------------------|
1 | Dance Lights | Brighten up the party... |
2 | Fog Machine | Add some fog for an e... |
Instead of taking up space storing the addon name in my invoice_items table, I'd like to just include the addon_id in the addon_1, addon_2, etc columns.
How do I then get the name of the addon when doing a query for invoice_item rows?
Right now I just have it programmed into the page that if addon_id == 1, echo "Dance Lights", etc but I'd like to do it in the query. Here is my current query:
$invoice_items_SQL = "
SELECT invoice_items.*, packages.*
FROM `invoice_items`
INNER JOIN packages ON invoice_items.invoice_item_id = packages.package_id
WHERE `event_id` = \"$event_id\"
";
So I'm able to do this with packages, but only because there's just one package_id per row, but there are up to 9 addons :(
The most direct way of doing it is to join onto the table multiple times. That's a bit naff though because you'll write almost the same thing 9 times.
Another, better way would be to restructure your tables - you need another table with 2 data columns: invoice_id and addon_id. You then need either an auto-inc primary column, or use both of those existing columns as a dual primary key. So this is a many-to-many junction table.
From there you can can query without having 9 repetitive joins, but you will get a row of each package for every addon it has (so if it has three addons it will appear three times in the results). And then from there you can use GROUP_CONCAT to concatenate the names of the addons into a single field so that you only get one row per invoice.
I have two table
one table is alldata ( here info_id is a text field data inserted using php )
=================
id | info_id
=================
1 | 2, 3, 5, 9
2 |
=================
second table is info
=================
id | name
=================
1 | one
2 | two
3 | three
4 | four
5 | five
6 | six
7 | seven
9 | eight
9 | nine
=================
now I want to select list of data from table two where data id will be matched with table one first item info_id data
my query is
SELECT i.* FROM `info` as i,`alldata` as a where i.id IN(a.info_id) and a.id=1
my query works but select only one item from table two.But there are multiple matched.
You have a very poor database design. First, storing numeric ids as strings is a bad idea -- numbers should be stored as numbers. Second, SQL offers this great data structure for storing lists. It is called a table, not a string.
You should really have a junction table, one one row per id and info_id.
That said, sometimes we a struck with substandard data structure. MySQL offers support for this. You can use:
SELECT i.*
FROM `info` i JOIN
`alldata` a
ON FIND_IN_SET(i.id, REPLACE(a.info_id, ', ', ',') ) > 0
WHERE a.id = 1;
You should also learn to use proper, explicit join syntax. If you use this method, instead of fixing the database design, you are not allowed to complain about performance. MySQL cannot take advantage of things like indexes to improve the performance of this type of query.
I have many a times tried using nested query for MySQL in PHP, but it does not work. Is it not possible to do nested/Joins queries?
Just a Scenario:
I have two tables one table with user id and the other with data. User logins and with sessions I have to cross check two different tables with user id (user and data). Is it not possible to nest/join these two tables to write a single query statement.
In short is nesting or joining two or more tables permitted in PHP coding?
YES, it is possible to join two or more tables in MySQL (and therefore, also when using PHP).
You need to post your table schema, if you want us to show a relevant join query. You could, however, try something like:
SELECT * FROM user AS t1
CROSS JOIN data AS t2
ON t1.userid=t2.userid
WHERE t1.userid='154'
(This query presumes that there always will be one row with the userid in both tables. You should use LEFT JOIN instead of CROSS JOIN to return a row even if there is no row in data for the userid. 154 is just an example userid.)
Have a look at http://dev.mysql.com/doc/refman/5.5/en/join.html for information on the JOIN syntax.
users
| user_id | username | password | enabled |
|---------|----------|----------|---------|
| 1 | john | sgsd2gg | 1 |
| 2 | jane | sdshdhd | 0 |
users_data
|udata_id| user_id | some_column |
|--------|---------|-------------------|
| 1 | 1 | Some title |
| 2 | 2 | another title |
Since you haven't posted your table schema, I can't give you an exact solution. But supposing you have a users table and a users_data table, where users_data are owned by a user. You can do a join on the table to retrieve all the data.
SELECT * -- Don't select all fields unless you need it
FROM users U LEFT JOIN users_data UD ON U.user_id = UD.user_id
WHERE U.user_id = 1
This would pull all the records for user with an ID of 1. This is a very simplistic join, but it should give you an idea.
Here's an example that visually describes the different options you can use : SQL Join Differences
I have one table GAMES and another PLAYERS. Currently each "game" has a column for players_in_game but I have nothing reciprocating in the PLAYERS table. Since this column is an array (Comma separated list of the player's ID #s) I'm thinking that it would probably be better to have each player's record also contain a list of the games they are a member of. On the other hand, duplicating the information in two separate tables might actually require more DB calls.
For perspective, there aren't likely to be more then a dozen players in a game (generally 4-6 is the norm) but there could potentially be a large number of games.
Is there a good way to figure out which would be more efficient?
Thanks.
Normalization is generally a good thing. Comma delimited lists in tables is a sign that a table is in desperate need of a foreign key. If you're worried about extra queries, check out JOINING
dbo.games
+----+----------+
| id | name |
+----+----------+
| 1 | war |
| 2 | invaders |
+----+----------+
dbo.players
+----+----------+---------+
| id | name | game_id |
+----+----------+---------+
| 1 | john | 1 |
| 2 | mike | 1 |
+----+----------+---------+
SELECT games.name, count(players.id) as total_players FROM games INNER JOIN players ON games.id = players.game_id GROUP BY games.name;
Result:
+-----------+--------------+
| name |total_players |
+-----------+--------------+
| war | 2 |
| invaders | 0 |
+-----------+--------------+
Sidenote: Go Hokies :)
Oh god, please don't use CSVs!! I know it's tempting when you're new to SQL, but it becomes unqueryable...
You need 3 tables: games, players, and players_in_games. games and players should each have a primary auto-incrementing key like id, and then players_in_games needs just two fields, player_id and game_id. This is called a "many to many" relationship. A player can play many games, and a game can have many players.
The right answer is a table called PlayersInGames that has a player id and a game id per row.
I would create a third table that links the players and games. Your comma-delimited list is effectively a third table, but parsing your list is almost certainly going to be less efficient than letting the database do it for you.
Ask yourself what happens if you remove a row from the GAME table. Now you'll have to loop over all the PLAYER rows, parse the list, figure out which ones contain a reference to the removed GAME, and then update all the lists.
Bad design. Let SQL do what it was born for. The query will be fast enough if you index it properly. Micro-optimizations like this are the wrong approach.