I'm trying create a MySQL query which will return a row (or more, but I'm only interested in a single row) an area suggestion when provided with a postcode.
So, I have a table like so
area_id | postcode_start
1 | NE
2 | DL
3 | DL1
4 | DL2
5 | DL6
...
And I wish to provide a postcode, for example DL5 8TB and for it to return the row 1 | DL as the first characters match.
Another example DL6 4GH would return two rows, 5 | DL6 and 2 | DL
SELECT *
FROM (`area_postcodes`)
WHERE CONCAT(LOWER(`area_postcodes`.`postcode_start`),'%')
LIKE 'dl5 8tb';
Apparently it's a valid query but it always returns an empty set.
You'll see I've added the wildcard % to the other side of the query but it doesn't seem to work and I don't know where else to even consider guessing how to go about it, it's almost like the reverse of a normal MySQL LIKE query.
You were very close:
SELECT
*
FROM
area_postcodes
WHERE
'dl5 8tb' LIKE CONCAT(postcode_start, '%');
Related
I was testing my application(an ERP system) by programming a tester that will do a fixed scenario of 30 steps of things like this
//pseudo code(PHP)
public function runScenario1Test(){
V2_1Tester::resetDatabase();
V2_1Tester::insert60Companies();
V2_1Tester::insert2000Items();
V2_1Tester::insert100Purchases();
V2_1Tester::insert100Sales();
//do some other stuff
V2_1Tester:checkResults();
}
Although every time I run the test of the same code, same data, all inputs were the same, I was getting different results sometimes!!!
My head was going to blow up, and after 4 days of investigations, tears, and even bad database dreams by night, it turns out that the bug was in a query that returns different results sometimes. It is something like this
+-----+--------------+-----------+------+--------+
| ID | date | direction | col3 | col4 |
+-----+--------------+-----------+------+--------+
| 1 | 2018-03-03 | in | 6 | 100.50 |
| 2 | 2018-03-03 | in | 6 | 350.75 |
+-----+--------------+-----------+------+--------+
-- more ~ 3000 rows
$query = "SELECT * FROM table ORDER BY date, direction, col3";
this query sometimes returns 1 then 2 and some other times 2 then 1.
I fixed the query by adding additional level for ordering ID
$query = "SELECT * FROM table ORDER BY date, direction, col3, ID";
But I don't understand why MySQL behaves like this ?, In other words what are the rules that MySQL will follow for the rows that are the same for all order-by columns ? and why it is changing ?
In SQL, order by is not stable. That means that when the keys are the same, the ordering can be in any order.
This is actually obvious. SQL tables represent unordered sets. There is no ordering unless a column specifies the ordering.
So, you have done the right thing by including the id as the final key. This ensures that the order will be well-defined because there are no duplicate keys.
My table looks something like this:
| id (int) | sentence (varchar) |
I want to find all rows that are almost the same except for one particular word. Eg:
| 230 | test |
| 321 | test sth |
...
| 329 | is (sth) it?
| 923 | is it?
The word that can be different is sth in this case. Ideally I could use some sort of "array" with the list of words that can be different.
Is this something I could do purely in SQL?
Just an untested quick shot, sorry, but I think you could do something like
SELECT * FROM table GROUP BY REPLACE(text, 'sth', '')
You can use SOUNDEX. So with the examples that you gave, these queries:
SELECT SOUNDEX('test')
SELECT SOUNDEX('test sth')
SELECT SOUNDEX('is (sth) it?')
SELECT SOUNDEX('is it?')
return these results:
T230
T230
I200
I200
That means that the first two and the second two sound like each other. What I can't be sure of is how well this will work with your actual data, you're just going to have to try it.
Is there a way I can store multiple values in a single cell instead of different rows, and search for them?
Can I do:
pId | available
1 | US,UK,CA,SE
2 | US,SE
Instead of:
pId | available
1 | US
1 | UK
1 | CA
1 | SE
Then do:
select pId from table where available = 'US'
You can do that, but it makes the query inefficient. You can look for a substring in the field, but that means that the query can't make use of any index, which is a big performance issue when you have many rows in your table.
This is how you would use it in your special case with two character codes:
select pId from table where find_in_set('US', available)
Keeping the values in separate records makes every operation where you use the values, like filtering and joining, more efficient.
you can use the like operator to get the result
Select pid from table where available like '%US%'
I have a simple MySQL table made up of words and an associated number. The numbers are unique for each word. I want to find the first word whose index is larger than a given number. As an example:
-----------------------
| WORD: | F_INDEX: |
|---------------------|
| a | 5 |
| cat | 12 |
| bat | 4002 |
-----------------------
If I was given the number "9" I would want "cat" returned, as it is the first word whose index is larger than 9.
I know that I can get a full list of sorted rows by querying:
SELECT * FROM table_name ORDER BY f_index;
But would, instead, like to make a MySQL query that does this. (The confusion lies in the fact that I'm unsure as to how to keep track of the current row in my query). I know can loop with something like this:
CREATE PROCEDURE looper(desired_index INT)
BEGIN
DECLARE current_index int DEFAULT 0
// Loop here, setting current_index to whatever the next rows index is,
// then do a comparison to check it to our desired_index, breaking out
// if it is greater.
END;
Any help would be greatly appreciated.
Try this:
SELECT t.word
, t.f_index
FROM table_name t
WHERE t.f_index > 9
ORDER
BY t.f_index
LIMIT 1
It is much more efficient to have the database return the row you need, than it is to pull a whole bunch of rows and figure out which one you need.
For best performance of this query, you will want an index ON table_name (f_index,word).
Why don't you just use MYSQL statement to retrieve the first item you found from f_index where the f_index is greater than the value your pass in.
For example :
select word from table_name
where f_index > desired_index
order by f_index
limit 1
I have a table that has a comma separated list of ids in one of the fields (not my doing). I want to know if I can use LIKE to match a number in this string? The problem is I don't want to get similar numbers. Is there a way to match a number with no numeric charcters on either side?
SELECT * FROM table WHERE activitiesids LIKE 6
| activitiesids |
---+---------------+---
| 3,16,8,6 |
---+---------------+---
| 6 |
---+---------------+---
| 7,560 |
---+---------------+---
Haven't tested but you can try something like this:
SELECT * FROM table WHERE activitiesids REGEXP '[[:<:]][0-9]+[[:>:]]';
Something like that:
WHERE ids LIKE '%,16,%' OR ids LIKE '%,16' OR ids LIKE '16,%';
Postgresql even has pattern matching - I don't know for mysql:
WHERE ids ~ '^(.*,)?16(,.*)?$';