Split a database query string using regex in ruby

You might be able to do this with regex but here's a parser that may work for your use case. It can surely be improved but it should work.

require 'time'

def parse(sql)
  arr = []
  split = sql.split(' ')
  date_counter = 0
  split.each_with_index do |s, i|
    date_counter = 2 if s == 'BETWEEN'
    time = Time.parse(s.strip) rescue nil
    date_counter -= 1 if time
    arr << i+1 if date_counter == 1
  end
  arr.select(&:even?).each do |index|
    split.insert(index + 2, 'SPLIT_ME')
  end
  split = split.join(' ').split('SPLIT_ME').map{|l| l.strip.gsub(/(AND)$/, '')}
  split.map do |line|
    line[/^AND/] ? line.split('AND') : line
  end.flatten.select{|l| !l.empty?}.map(&:strip)
end

This is not really a regex, but more a simple parser.

1. This works by matching a regex from the start of the string until it encounters a whitespace followed by either and or between followed by a whitespace character. The result is removed from the where_cause and saved in statement.
2. If the start of the string now starts with a whitespace followed by between followed by a whitespace. It is added to statement and removed from where_cause with anything after that, allowing 1 and. Matching stops if the end of the string is reached or another and is encountered.
3. If point 2 didn't match check if the string starts with a whitespace followed by and followed by a whitespace. If this is the case remove this from where_cause.
4. Finally add statement to the statements array if it isn't an empty string.

All matching is done case insensitive.

where_cause = "created_at BETWEEN '2018-01-01T00:00:00+05:30' AND '2019-01-01T00:00:00+05:30' AND updated_at BETWEEN '2018-05-01T00:00:00+05:30' AND '2019-05-01T00:00:00+05:30' AND user_id = 5 AND status = 'closed'"

statements = []
until where_cause.empty?
  statement = where_cause.slice!(/\A.*?(?=[\s](and|between)[\s]|\z)/mi)

  if where_cause.match? /\A[\s]between[\s]/i
    between = /\A[\s]between[\s].*?[\s]and[\s].*?(?=[\s]and[\s]|\z)/mi
    statement << where_cause.slice!(between)
  elsif where_cause.match? /\A[\s]and[\s]/i
    where_cause.slice!(/\A[\s]and[\s]/i)
  end

  statements << statement unless statement.empty?
end

pp statements
# ["created_at BETWEEN '2018-01-01T00:00:00+05:30' AND '2019-01-01T00:00:00+05:30'",
#  "updated_at BETWEEN '2018-05-01T00:00:00+05:30' AND '2019-05-01T00:00:00+05:30'",
#  "user_id = 5",
#  "status = 'closed'"]

Note: Ruby uses \A to match the start of the string and \z to match the end of a string instead of the usual ^ and $, which match the beginning and ending of a line respectively. See the regexp anchor documentation.

You can replace every [\s] with \s if you like. I've added them in to make the regex more readable.

Keep in mind that this solution isn't perfect, but might give you an idea how to solve the issue. The reason I say this is because it doesn't account for the words and/between in column name or string context.

The following where cause:

where_cause = "name = 'Tarzan AND Jane'"

Will output:

#=> ["name = 'Tarzan", "Jane'"]

This solution also assumes correctly structured SQL queries. The following queries don't result in what you might think:

where_cause = "created_at = BETWEEN AND"
# TypeError: no implicit conversion of nil into String
# ^ does match /\A[\s]between[\s]/i, but not the #slice! argument 
where_cause = "id = BETWEEN 1 AND 2 BETWEEN 1 AND 3"
#=> ["id = BETWEEN 1 AND 2 BETWEEN 1", "3"]

I'm not certain if I understand the question, particularly in view of the previous answers, but if you simply wish to extract the indicated substrings from your string, and all column names begin with lowercase letters, you could write the following (where str holds the string given in the question):

str.split(/ +AND +(?=[a-z])/)
  #=> ["created_at BETWEEN '2018-01-01T00:00:00+05:30' AND '2019-01-01T00:00:00+05:30'",
  #    "updated_at BETWEEN '2018-05-01T00:00:00+05:30' AND '2019-05-01T00:00:00+05:30'",
  #    "user_id = 5",
  #    "status = 'closed'"]

The regular expression reads, "match one or more spaces, followed by 'AND', followed by one or more spaces, followed by a positive lookahead that contains a lowercase letter". Being in a positive lookahead, the lowercase letter is not part of the match that is returned.