Hi, On 2022-06-27 19:00:44 +0000, Ma, Marcus wrote: > If I understand correctly, when a Sequential Scan takes place, the ExecScan > function (located in executor/execScan.c) does not retrieve all attributes > per tuple in the TupleTableSlot and only retrieves the necessary attribute. > So for example, let’s imagine we have a table t1 with 3 number fields, c1, > c2, and c3. So in the command: > > Select * from t1 where t1.c1 > 500; > > The returned TupleTableSlot will have its field of tts_values in the form (X, > 0, 0), where X is the real value of t1.c1 but the fields of c2 and c3 are not > actually retrieved because they aren’t used. Similarly, for the command: > > Select * from t1; > > The TupleTableSlot will always return the values of (0, 0, 0) because no > comparisons are necessary. I am working on code where I’ll need access to > attributes that aren’t listed in any qualification – what code should I > change in execScan, or nodeSeqScan to be able to retrieve any attribute of a > tuple? Basically, being able to make execScan return (X, Y, Z) instead of > (0, 0, 0) even if the command doesn’t use any attribute comparisons.
You'll need to tell the planner that those columns are needed. It's not just seqscans that otherwise will discard / not compute values. Where exactly do you need those columns and why? Greetings, Andres Freund
