[rql rewrite] backout 7177:f2a976cf7dac : since EXISTS is the variable scope, we want to insert snippets here anyway (other solution would be to NOT insert snippets at all in such case). Closes #1625464

if repo.system_source.dbdriver == 'postgres':
    sql('ALTER TABLE appears ADD COLUMN weight float')
    sql('UPDATE appears SET weight=1.0 ')