我无法正确加入REGEXP mysql

Question

I'm sick of beating by head over the wall with this one. So far nobody on our team can figure out why it's not working.

I have two tables that I need to check rows against each other on each of them for accuracy.

Table1

feature_name | state_alpha | population data
city1        |     MI      |          34567
city3        |     MI      |          4567
city4        |     MI      |          5567

Table2

city
city1
city2
city3

I have gotten the LEFT JOIN to work with this query:

SELECT f.feature_name, f.population_data, f.state_alpha, bc.city
FROM `fedcodes` AS f
left JOIN bob_cities AS bc ON bc.city
REGEXP concat( f.feature_name )
WHERE f.population_data >1000
AND f.state_alpha = "MI"
AND f.feature_name NOT
REGEXP 'city of'
AND f.feature_name NOT regexp 'town of'

This returns exactly what I expect it to. All values in the left column are there and NULL values in the right column where there are no matches. Which solves what I need to know: "Which cities are in table1 that are not also in table2."

Next I need to know which cities are in table2 that are not in table1 based on the WHERE clause. A RIGHT JOIN should do this. Correct?

However I cannot get it to work and I feel like I have tried every possible permutation of the query and have crashed my home server quite a few time in the process.

Why doesn't this work?

SELECT f.feature_name, f.population_data, f.state_alpha, bc.city
FROM `fedcodes` AS f
RIGHT JOIN bob_cities AS bc ON f.feature_name
REGEXP concat( bc.city )
WHERE f.population_data >1000
AND f.state_alpha = "MI"
AND f.feature_name NOT
REGEXP 'city of'
AND f.feature_name NOT regexp 'town of'

I've also tried this.

SELECT f.feature_name, f.population_data, f.state_alpha, bc.city
FROM `fedcodes` AS f
RIGHT JOIN bob_cities AS bc ON (f.feature_name
REGEXP concat( bc.city )
AND f.population_data >1000
AND f.state_alpha = "MI"
AND f.feature_name NOT
REGEXP 'city of'
AND f.feature_name NOT regexp 'town of')

I'm using REGEXP because even though the names in the rows are the same in both tables (feature_name = city) if I use the = operator it doesn't work(even in the LEFT JOIN that I have working)

All that happens when I run the queries in phpmyadmin is the server stays busy for a while then freezes.

Answer 1

Try nesting fedcodes , with the other WHERE clauses that only it needs:

SELECT f.feature_name, f.population_data, f.state_alpha, bc.city
FROM (SELECT feature_name, population_data, state_alpha
    FROM `fedcodes`
    WHERE population_data >1000
    AND state_alpha = "MI"
    AND feature_name NOT
    REGEXP 'city of'
    AND feature_name NOT regexp 'town of'
    ) AS f
RIGHT JOIN bob_cities AS bc ON f.feature_name
REGEXP concat( bc.city )

It may be that your query is having trouble performing matches on null values?

Answer 2

Just flip around the order of the joins ...

 SELECT f.feature_name, f.population_data, f.state_alpha, bc.city
   FROM bob_cities as bc
   LEFT JOIN `fedcodes` as f ON   ON bc.city  REGEXP concat( f.feature_name )
   ...

That should work.

If you're crashing mysqld with a query you should consider reporting a bug to the mysql team.

Answer 3

Try fixing the REGEXP portion of the second query to match the first:

SELECT f.feature_name, f.population_data, f.state_alpha, bc.city
FROM `fedcodes` AS f
RIGHT JOIN bob_cities AS bc ON bc.city REGEXP f.feature_name
...

Better yet use LOCATE (assuming = won't work, = is even better):

SELECT f.feature_name, f.population_data, f.state_alpha, bc.city
FROM `fedcodes` AS f
RIGHT JOIN bob_cities AS bc ON 0 < LOCATE(TRIM(f.feature_name), TRIM(bc.city))
...

Remember, REGEXP usually expects a pattern. It's a lot more complicated than contains() or equals().

Answer 4

First I would like to thank everyone for their response. I tried everything that you guys suggested to no avail. But as it turns out it wasn't the query after all. Which is why nothing I tried worked.

A team member found that the data in the database was corrupt somehow. I'm not sure of the details but the origin of the data was from a CSV and he said that it was bad in there. He gave me a new copy of the CSV (cleaned) I recreated the database with it and everything worked as it should.

Here is the working query:

SELECT DISTINCT f.feature_name, f.population_data, b.city
FROM `fedcodes` f
RIGHT JOIN bob_cities_fix b ON f.feature_name = b.city
AND f.population_data =0
AND f.state_alpha = "al"

A RIGHT JOIN by the book working exactly the way it needs to.

You may notice in the original query I was filtering the data of cities over 1000 and it turns out I needed to find cities with no population in the database for the RIGHT JOIN to accurately return what I needed.

However this was an easy fix once I was getting feedback from the queries rather than freezing PHPmyadmin.