I think I figured it out. In knex.js, say you specify a table like: knex.select( ‘*’ ).from( ‘Users’ ) Then you can just add the AS keyword within the quotes of the table name to alias it, like so: knex.select( ‘*’ ).from( ‘Users AS u’ ) ..and you can do this for column names, too; … Read more
This kind of query should work – after rewriting with explicit JOIN syntax: SELECT something FROM master parent JOIN master child ON child.parent_id = parent.id LEFT JOIN second parentdata ON parentdata.id = parent.secondary_id LEFT JOIN second childdata ON childdata.id = child.secondary_id WHERE parent.parent_id = ‘rootID’; The tripping wire here is that an explicit JOIN binds … Read more
Starting from Django 1.4 prefetch_related does what you want. Parent.objects.prefetch_related(‘child_set’) Related(!) django docs : https://docs.djangoproject.com/en/dev/ref/models/querysets/#prefetch-related.
Don’t mix the comma operator with JOIN – they have different precedence! There is even a warning about this in the manual: However, the precedence of the comma operator is less than of INNER JOIN, CROSS JOIN, LEFT JOIN, and so on. If you mix comma joins with the other join types when there is … Read more
It’s a perfectly legitimate solution for some designs. Say you have a hierarchy of one-to-many relations like Customer – Order – Basket – Item – Price, etc., which can be unfilled on any level: a Customer may have no Orders, an Order can have no Baskets, etc. In this case you issue something like: SELECT … Read more
Joins are processed left to right (unless parentheses dictate otherwise). If you LEFT JOIN (or just JOIN, similar effect) three groceries to one user you get 3 rows (1 x 3). If you then join 4 fishmarkets for the same user, you get 12 (3 x 4) rows, multiplying the previous count in the result, … Read more
SAMPLE. DELETE RECORD IN TABLE ‘A’ IS THERE ARE NOT RECORD IN TABLE ‘H’ DELETE A FROM ARTICULO_ALMACEN A LEFT JOIN HISTORICO_UNION H ON A.COD_ARTICULO = H.COD_ARTICULO AND A.COD_ALMACEN = H.COD_ARTICULO_ALMACEN AND A.TPROPIEDAD1 = H.PROPIEDAD1 AND A.TPROPIEDAD2 = H.PROPIEDAD2 AND A.TPROPIEDAD3 = H.PROPIEDAD3 WHERE H.COD_ARTICULO IS NULL