SQL search with REGEX instead with BETWEEN operator - mysql

Question

I have MySQL database, and inside table with ads. In one field of table of that database, data is being saved in json format. In that json formatted data, I have key which value contains price (with decimal values).
That field (named for example ad_data), which is saved in database field, contains (json) data like this:
{"single_input_51":"Ad 44 test.","price":"20.00","single_input_4":"ad test title, ad tes title, .","single_input_11":"8.8.2015.","single_input_5":"video test","single_input_6":"https://www.youtube.com/watch?v=nlTPeCs2puw"}
I would like to search in that field, so I can find price range that is searched. If for example, user sets in html form he wants to search in ranges from 100.00 do 755.00, SQL should return only rows where that field (which data is saved as json) contains those values that are from 100.00 to 755.00.
So basically, I would want to write something like this with REGEX in SQL for that json formatted contents of that field (numbers here are just examples, I must be able to to this for every starting and closing decimal number, and numbers I will pass programatically):
SELECT id, price FROM ads WHERE price BETWEEN 100.00 AND 755.00
What would be SQL command for that search via REGEX?

Answer 1

Don't use REGEX for doing the match, that will be painful. If you had a particular range of prices you were looking for, it might be doable, but to dynamically generate the regular expression to "work" for any specified range of prices, when the price could be two, three or more characters, that's going to be hard. (The REGEXP function in MySQL only returns a boolean indicating whether a match was found or not; it won't return the portion of the string that was matched.)
If I had to do a comparison on "price", I would parse the value for price out of the string, then cast that to a numeric value, and the do a comparison on that.
For example:
SELECT t.col
FROM mytable t
WHERE SUBSTRING_INDEX(SUBSTRING_INDEX(t.col,'"price":"',-1),'"',1) + 0
BETWEEN 100.00 AND 755.00
To answer the question you asked: what expression would you use to perform this match using a REGEX...
For "price between 100.00 and 755.00", using MySQL REGEXP, the regular expression you would need would be something like the second expression in the SELECT list of this query:
SELECT t.col
, t.col REGEXP '"price":"([1-6][0-9][0-9]\.[0-9][0-9]|7[0-4][0-9]\.[0-9][0-9]|75[0-4]\.[0-9][0-9]|755\.00)"' AS _match
FROM ( SELECT 'no' AS col
UNION ALL SELECT 'no "price":"14.00"def'
UNION ALL SELECT 'ok "price":"99.99" def'
UNION ALL SELECT 'ok "price":"100.00" def'
UNION ALL SELECT 'ok "price":"699.99" def'
UNION ALL SELECT 'ok "price":"703.33" def'
UNION ALL SELECT 'ok "price":"743.15" def'
UNION ALL SELECT 'ok "price":"754.99" def'
UNION ALL SELECT 'no "price":"755.01" def'
) t
The regular expression in this example is almost a trivial example, because the price values we're matching all have three digits before the decimal point.
The string used for a regular expression would need to be crafted for each possible range of values. The crafting would need to take into account prices with different number of digits before the decimal point, and handle each of those separately.
For doing a range check of price between 95.55 to 1044.44, that would need to be crafted into a regular expression to check price in these ranges:
95.55 thru 95.59 95\.5[5-9]
95.60 thru 95.99 95\.[6-9][0-9]
96.00 thru 99.99 9[6-9]\.[0-9][0-9]
100.00 thru 999.99 [1-9][0-9][0-9]\.[0-9][0-9]
1000.00 thru 1039.99 10[0-3][0-9]\.[0-9][0-9]
1040.00 thru 1043.99 1040[0-3]\.[0-9][0-9]
1044.00 thru 1044.39 1044\.[0-3][0-9]
1044.40 thru 1044.44 1044\.4[0-4]
It could be done, but the code to generate the regular expression string won't be pretty. (And getting it fully tested won't be pretty either.)

Answer 2

(#spencer7593 has a good point; here's another point)
Performance... If you have an index on that field (and the optimizer decides to use the index), then BETWEEN can be much faster than a REGEXP.
BETWEEN can use an index, thereby minimizing the number of rows to look at.
REGEXP always has to check all rows.