sql/postgres: fixed inspection of multicolumn indexes

[svstanev]

I have an unique index like this:

create unique index if not exists u_entity_name on entity (
  entity_type,
  coalesce(parent_id,0),
  name
);

which when inspected become like this:

index "u_entity_name" {
    unique = true
    type   = BTREE
    on {
      expr = "COALESCE(parent_id, (0)::bigint)"
    }
    on {
      expr = "COALESCE(parent_id, (0)::bigint)"
    }
    on {
      expr = "COALESCE(parent_id, (0)::bigint)"
    }
  }

Expected:

index "u_entity_name" {
    unique = true
    type   = BTREE
    on {
      column = column.entity_type
    }
    on {
      expr = "COALESCE(parent_id, (0)::bigint)"
    }
    on {
      column = column.name
    }
  }

Reason: incorrect index metadata query.

[a8m]

Why this change is needed?

[svstanev]

Each row of the indexesQuery returns an index part/column in a multicolumn index. As per the suggested query each part always has a valid expression but column only if it is created with a column name:

LEFT JOIN pg_attribute a ON (a.attrelid, a.attnum) = (idx.indrelid, idx.key)

If you mean why I have replaced the switch statement with an if that's because at that moment it seemed like the more obvious way to express the precedence of the column over the expression. Of course the switch also evaluates the cases in a fixed order so it's would work just fine in this case.

[a8m]

Thanks for the explanation. If you don't mind, please revert to the switch statement and I'll merge it.

[a8m]

💯

[a8m]

💯

[a8m]

Thanks for the contribution @svstanev 🙏🏻