Question

I need a regex that will determine if a given SQL statement has a WHERE clause. My problem is that the passed SQL statements will most likely be complex, so I can not rely on just the existence of the word WHERE in the statement.

For example this should match

SELECT Contacts.ID
     , CASE WHEN (Contacts.Firstname IS NULL) THEN ''
            ELSE CAST(Contacts.Firstname AS varchar)
       END AS Firstname
     , CASE WHEN (Contacts.Lastname IS NULL) THEN ''
            ELSE CAST(Contacts.Lastname AS varchar)
       END AS Lastname
     , CASE WHEN (tbl_ContactExtras.Prequalified=-1 OR
                  tbl_ContactExtras.Prequalified IS NULL) THEN ''
            WHEN tbl_ContactExtras.Prequalified=0 THEN 'No'
            WHEN tbl_ContactExtras.Prequalified=1 THEN 'Yes - Other'
            WHEN tbl_ContactExtras.Prequalified=2 THEN 'Yes'
            ELSE CAST(tbl_ContactExtras.Prequalified AS varchar)
       END AS Prequalified
FROM contacts
LEFT JOIN tbl_ContactExtras
ON tbl_ContactExtras.ContactID = Contacts.ID
WHERE (Contacts.Firstname LIKE 'Bob%')

and this should not match:

SELECT Contacts.ID
     , CASE WHEN (Contacts.Firstname IS NULL) THEN ''
            ELSE CAST(Contacts.Firstname AS varchar)
       END AS Firstname
     , CASE WHEN (Contacts.Lastname IS NULL) THEN ''
            ELSE CAST(Contacts.Lastname AS varchar)
       END AS Lastname
     , CASE WHEN (tbl_ContactExtras.Prequalified=-1 OR
                  tbl_ContactExtras.Prequalified IS NULL) THEN ''
            WHEN tbl_ContactExtras.Prequalified=0 THEN 'No'
            WHEN tbl_ContactExtras.Prequalified=1 THEN 'Yes - Other'
            WHEN tbl_ContactExtras.Prequalified=2 THEN 'Yes'
            ELSE CAST(tbl_ContactExtras.Prequalified AS varchar)
       END AS Prequalified
FROM contacts
LEFT JOIN tbl_ContactExtras
ON tbl_ContactExtras.ContactID = Contacts.ID

Those are examples of some of the simpler statements: a statement could have up to 30 CASE statements in it, or it could have none at all.

I need to programmatically add WHERE parameters, but doing this correctly requires knowing whether a WHERE clause is already present.

Any idea on a regex that would work for this? If not, any other ideas on how to tell the two apart?

Thanks,

Answer 1

This is not possible, since a WHERE clause may be arbitrarily nested inside the FROM clause.