Update specific records of MySQL table

Question

I am dealing with phone system and have to work with multiple service vendors. For one vendor I have a MySQL table country_codes like this -

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Answer 1

If you need to do the fix the data ONLY once, you can try this approach:

0) Backup your data, or better, run the query on copy of the data.

1) Creates a table that contains non-zero country codes. We need separate table because it says in MySQL manual that:

Currently, you cannot update a table and select from the same table in a subquery.

CREATE TABLE country_codes_list (
    country_code INT NOT NULL PRIMARY KEY
);

INSERT INTO country_codes_list
SELECT country_code
FROM country_codes
WHERE country_code <> 0;

2) Update all rows where country code is 0 by finding the country code that matches the beginning of the area code:

UPDATE country_codes AS country_codes_zero SET country_code = (
    SELECT country_code
    FROM country_codes_list
    WHERE country_codes_list.country_code = SUBSTRING(country_codes_zero.area_code, 1, LENGTH(country_codes_list.country_code))
) WHERE country_code = 0;

This could be a very slow query because it uses a co-related sub-query. But it should fix the data in one go.

Answer 2

Something like this should work, assuming you have a database called "testdb", and a table called "footable".

$link = mysql_connect("localhost", "username", "password1234");
mysql_select_db("testdb", $link);

$result = mysql_query("UPDATE footable SET country_code="93" WHERE country LIKE Afghanistan%", $link);
$result = mysql_query("UPDATE footable SET country_code="355" WHERE country LIKE Albania%", $link);

mysql_close($link);

Answer 3

You can create a table with countries only, i.e.:

INSERT INTO countries (country_code,country)
SELECT country_code,country FROM country_codes WHERE country_code=0

Then you can easily update your table

UPDATE country_codes cc, countries c
SET cc.country_code = c.country_code
WHERE LOCATE(c.country,cc.country)=1 AND cc.country_code=0

I haven't tested this, but I believe you can get the point.

Answer 4

update cc set
    country_code = t.country_code
from country_codes cc
join (
    select country_code, country, char_length(trim(cast(country_code as char))) as code_len
    from country_codes
    where country_code <> 0
) t on 
    t.country_code = cast(substr(cast(cc.area_code as char), 1, t.code_len) as signed integer) and
    cc.country_code = 0 and
    cc.country like concat(t.country, '%')

I've added cc.country like concat(t.country, '%') to condition to be more specific but it assumes that each cellular network name starts with its country name - so if it's not true omit it.

Added after @Sachyn comment:

Test code used on SQLZOO works fine, it is for testing only, it's not an update query:

select cc.*, t.country_code as new_country_code
from (
    select 93 as country_code, 93  as area_code , 'Afghanistan' as country union
    select 0  , 9375 , 'Afghanistan Cellular-AT' union
    select 0  , 9370 , 'Afghanistan Cellular-AWCC' union
    select 355, 355  , 'Albania' union
    select 0  , 35568, 'Albania Cellular-AMC' union
    select 0  , 35567, 'Albania Cellular-Eagle' union
    select 213, 213  , 'Algeria' union
    select 0  , 21377, 'Algeria Cellular-Djezzy' union
    select 0  , 2135 , 'Algeria Cellular-Wataniya'
) cc
join (
    select country_code, country, char_length(rtrim(cast(country_code as char))) as code_len
    from (
        select 93 as country_code, 93  as area_code , 'Afghanistan' as country union
        select 0  , 9375 , 'Afghanistan Cellular-AT' union
        select 0  , 9370 , 'Afghanistan Cellular-AWCC' union
        select 355, 355  , 'Albania' union
        select 0  , 35568, 'Albania Cellular-AMC' union
        select 0  , 35567, 'Albania Cellular-Eagle' union
        select 213, 213  , 'Algeria' union
        select 0  , 21377, 'Algeria Cellular-Djezzy' union
        select 0  , 2135 , 'Algeria Cellular-Wataniya'
    ) c
    where country_code <> 0
) t on 
    t.country_code = cast(substr(cast(cc.area_code as char), 1, t.code_len) as signed integer) and
    cc.country_code = 0 and
    cc.country like concat(t.country, '%')

Answer 5

Try this query -

UPDATE country_codes
SET country_code := @c := IF(@c IS NOT NULL AND country_code = 0, @c, country_code)
ORDER BY CAST(area_code AS CHAR)