Question

I need a way to search for a word within an SQL query, and to be able to determine whether or not that word is within a subquery or the main query.

For example:

SELECT * 
FROM products 
WHERE id NOT IN (SELECT product_id 
                 FROM tagmap 
                 WHERE tag_id = 1)

I need to replace the instance of the word WHERE with, say, WHERE 1=1 AND in the query string, but only in the main query, not in the subquery.

This is only an example of the issue I’m facing. The real queries are much bigger than this and contain several subqueries! Also, there are hundreds of queries I need to do this for, so I need to be able to do this automatically.

Answer 1

I think the following regex:

(?<!\(.*)\b(WHERE)\b|\b(WHERE)\b(?!.*\))

will match any instance of “WHERE”:

• that occurs to the left of the first opening parenthesis, or
• that occurs to the right of the last closing parenthesis.

ie Won’t detect instances of WHERE that occur inside a (..).

It’s worked on the few test cases I’ve tried… and I’m not going to do any more testing without further clarifcation of your requirements…

EG below, I’ve indicated the matched instances by surrounding with tildes: ~WHERE~.

SELECT * 
FROM products 
~WHERE~ id NOT IN 
    (SELECT product_id FROM tagmap WHERE tag_id = 1 and (SELECT true WHERE something) );

SELECT x FROM y ~WHERE~ z = z;

SELECT Count(*) 
FROM (Select rows FROM table WHERE filter) 
~WHERE~ z

I’d strongly recommend you test this thoroughly before relying on it.

---

EDIT: A basic .NET implementation… because I’ve got VS open at the moment… 😉

using System;
using System.Text;
using System.Text.RegularExpressions;
using System.IO;

class Program
{
    static void Main(string[] args)
    {
        StreamReader sr = new StreamReader("pathToSqlScript.sql");
        string oldSQLString = sr.ReadToEnd();
        string newSQLString = Regex.Replace(oldSQLString, @"(?<!\(.*)\b(WHERE)\b|\b(WHERE)\b(?!.*\))", @"WHERE 1=1 AND");
        StreamWriter sw = new StreamWriter("newSqlScript.sql");
        sw.Write(newSQLString);
    }
}

---

EDIT: To do this in a text editor…

Visual Studio will allow you do perform a search/replace based on a regex. I’d imagine something like Notepad++ would do it (at least with the aid of a plugin). Or this might help you: http://www.regular-expressions.info/editpadpro.html

Otherwise, knock up something that’ll read/modify your text file, eg using PHP, .NET, Java, ….