Extracting a targeted subsequence from a string in JavaScript

Question

Extracting a targeted subsequence from a string in JavaScript

I have a dynamic string that is created in one of the following ways:

var q = "FROM Table SELECT sum(1), count(2), avg(3) where x='y'

var q = "SELECT min(1), max(2), average(3) FROM Table where z='x' since y days ago

The values after the select statement can vary from 1 to 10. I am trying to develop a method to always extract the selected values into an array, but I am struggling with the variable nature (the dynamically constructed string and the varying number of selects).

In essence, I want the final result to look like this:

['sum(1)', 'count(2)', 'avg(3)']

Currently, my approach involves the following code, but it relies on the string being organized in a specific way (always starting with SELECT and having a where clause after the fields to extract):

let splitQ = q.match(".*SELECT(.*)where");
let selects = splitQ[1].trim().split(",");

javascript split

Answer 1

Answer №1

Below is a functional solution provided with certain assumptions about the query (in lowercase form).

The values are assumed to appear after the first occurrence of the word 'select.'
If the query begins with 'from,' the values are expected to end before encountering 'where.'
If the query starts with 'select,' the values should end before reaching 'from.'

const test1 = "FROM Table SELECT avg(1), avg(2), avg(3) where x='y'";

const test2 = "SELECT avg(1), avg(2), avg(3) FROM Table where z='x' since x days ago";



function extractValues(query) {
  // in both scenarios, the values always come directly after 'select '
  const valuesComeAfterMe = 'select ';
  query = query.toLowerCase();
  let valuesEndBeforeMe;
  // conditionally handle both query syntaxes
  if (query.startsWith('from')) {
    valuesEndBeforeMe = ' where';
  } else if (query.startsWith('select')) {
    valuesEndBeforeMe = ' from';
  } else {
    throw Error('query not handled');
  }
  // remove start
  query = query.slice(query.indexOf(valuesComeAfterMe) + valuesComeAfterMe.length);
  // remove end
  query = query.slice(0, query.indexOf(valuesEndBeforeMe));
  // split values and trim whitespace
  return query.split(',').map(item => item.trim());
}

console.log(extractValues(test1));
console.log(extractValues(test2));

Answer 2

Below is a functional solution provided with certain assumptions about the query (in lowercase form).

The values are assumed to appear after the first occurrence of the word 'select.'
If the query begins with 'from,' the values are expected to end before encountering 'where.'
If the query starts with 'select,' the values should end before reaching 'from.'

const test1 = "FROM Table SELECT avg(1), avg(2), avg(3) where x='y'";

const test2 = "SELECT avg(1), avg(2), avg(3) FROM Table where z='x' since x days ago";



function extractValues(query) {
  // in both scenarios, the values always come directly after 'select '
  const valuesComeAfterMe = 'select ';
  query = query.toLowerCase();
  let valuesEndBeforeMe;
  // conditionally handle both query syntaxes
  if (query.startsWith('from')) {
    valuesEndBeforeMe = ' where';
  } else if (query.startsWith('select')) {
    valuesEndBeforeMe = ' from';
  } else {
    throw Error('query not handled');
  }
  // remove start
  query = query.slice(query.indexOf(valuesComeAfterMe) + valuesComeAfterMe.length);
  // remove end
  query = query.slice(0, query.indexOf(valuesEndBeforeMe));
  // split values and trim whitespace
  return query.split(',').map(item => item.trim());
}

console.log(extractValues(test1));
console.log(extractValues(test2));

Extracting a targeted subsequence from a string in JavaScript

Answer №1

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