null
Do nullable columns occupy additional space in PostgreSQL?
Basically, NULL values occupy 1 bit in the NULL bitmap. But it’s not that simple. The null bitmap (per row) is only allocated if at least one column in that row holds a NULL value. This can lead to a seemingly paradoxic effect in tables with 9 or more columns: assigning the first NULL value … Read more
MySQL Integer 0 vs NULL
Using NULL is preferable, for two reasons: NULL is used to mean that the field has no value, which is exactly what you’re trying to model. If you decide to add some referential integrity constraints in the future, you will have to use NULL.
Assign value to variable only if is not null – Kotlin
Another solution if You don’t want to return from function just yet: x?.let{ y = it } Which checks if x is non-null then passes it as the only parameter to the lambda block. This is also a safe call in case your x is a var.
How to select columns from a table which have non null values?
Have a look as statistics information, it may be useful for you: SQL> exec dbms_stats.gather_table_stats(‘SCOTT’,’EMP’); PL/SQL procedure successfully completed. SQL> select num_rows from all_tables where owner=”SCOTT” and table_name=”EMP”; NUM_ROWS ———- 14 SQL> select column_name,nullable,num_distinct,num_nulls from all_tab_columns 2 where owner=”SCOTT” and table_name=”EMP” order by column_id; COLUMN_NAME N NUM_DISTINCT NUM_NULLS —————————— – ———— ———- EMPNO N 14 … Read more
Standard SQL boolean operator IS vs. equals (=) operator
That’s a new one for me. If I read that correctly the <boolean value expression> grammar defines three predicates solely for use with the boolean datatype IS TRUE, IS FALSE, IS UNKNOWN. These differ from their equality counterparts in that they only evaluate to True or False. Never to Unknown. i.e. UNKNOWN = TRUE would … Read more
Release, Dealloc, and the Self reference
A1) [nil release] is fine (won’t do anything) A2) No. Don’t touch objects after they’ve been deallocated. They should be set to nil after they are released. A3) It’s not necessary to set a released pointer to nil, but you get dangling pointers (i.e., you can’t tell if an object is valid or not). Setting … Read more
JSON field set to null vs field not there
Use json.RawMessage to “delay” the unmarshaling process to determine the raw byte before deciding to do something: var data = []byte(`{ “somefield1″:”somevalue1”, “somefield2”: null }`) type Data struct { SomeField1 string SomeField2 json.RawMessage } func main() { d := &Data{} _ = json.Unmarshal(data, &d) fmt.Println(d.SomeField1) if len(d.SomeField2) > 0 { if string(d.SomeField2) == “null” { … Read more
Assigned vs nil
TL;DR The official documentation states Assigned(P) corresponds to the test P <> nil for a pointer variable, and @P <> nil for a procedural variable. Hence, for a non-procedural pointer variable (such as a variable of type PInteger, PMyRec, TBitmap, TList<integer>, or TFormClass), Assigned(P) is the same thing as P <> nil. However, for a … Read more