The order in which table aliases are references in the `where` clause must match the order in which the aliases are declared. For example: ``` sql select a.id from aaa as a, bbb as b where b.id = 7 and a.name = b.name; ``` returns the error message [Cannot read property 'alias' of undefined](http://ql.io/console?s=select%20a.id%20from%20aaa%20as%20a,%20bbb%20as%20b%20where%20b.id%20=%207%20and%20a.name%20=%20b.name;) however the structurally equivalent form (with the match on `a.id` instead of `b.id`) ``` sql select a.id from aaa as a, bbb as b where a.id = 7 and a.name = b.name; ``` produces [no error](http://ql.io/console?s=select%20a.id%20from%20aaa%20as%20a,%20bbb%20as%20b%20where%20a.id%20=%207%20and%20a.name%20=%20b.name;).