Simple query to SQL parser

parser

// ================================
// Simple query to SQL parser
// 
// Copy and paste to https://pegjs.org/online
// 
// It parses expressions like:
//
//     (flag == True) AND (name == 'Paco' OR (name LIKE '%garcia%') OR (age > 18 AND age <= 45))
//
// ================================

start = ex:Expression { return "SELECT * FROM myTable WHERE " + ex; }

Expression
  = head:Term tail:(_ ("AND" / "OR") _ Term)* {
      return tail.reduce(function(result, element) {
        if (element[1] === "OR") { return "(" + result + " OR " + element[3] + ")"; }
        if (element[1] === "AND") { return "(" + result + " AND " + element[3] + ")"; }
      }, head);
    }

Term
  = head:Factor tail:(_ ("AND" / "OR") _ Factor)* {
      return tail.reduce(function(result, element) {
        if (element[1] === "OR") { return "(" + result + " OR " + element[3] + ")"; }
        if (element[1] === "AND") { return "(" + result + " AND " + element[3] + ")"; }
      }, head);
    }
    / Factor

Factor
  = "(" _ expr:Expression _ ")" { return expr; }
  / Condition
  
Condition 
  = id:Identifier _ op:Operator _ val:Value { return "'" + id + "' " + op + " " + val; }
  
Operator = _ ("!=" / "<=" / "<" /  "==" / ">=" / ">" / "LIKE") _ { return text() }
  
Boolean
  = "True" / "False"

Identifier
  = [a-zA-z][a-zA-Z0-9]* { return text(); }
  
Value
  = String / Integer / Boolean { return text(); }

String
  = "\"" [a-zA-Z0-9%]* "\"" { return text(); }
  / "'" [a-zA-Z0-9%]* "'" { return text(); }

Integer
  = [0-9]+ { return parseInt(text(), 10); }

_ "whitespace"
  = [ \t\n\r]*