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Install PL/SQL Developer from Control Panel -> Run Advertised Programs. When you run it it'll ask for the Oracle logon details, e.g. username / password / database = dwh (or sipr.yims.york). Click the New icon and choose SQL Window. Put the query in here - to run it, press F8 or click the yellow Execute cog icon. PL/SQL Developer has some nice features like the Beautifier, which lays your code out in a standard, sometimes more legible form.
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