PostgreSQL determines whether it is an empty coalesce

COALESCE (EXPR1,EXPR2,EXPR3 ...)

Until a non-null value is found, the right-hand expression does not participate in the operation, and if all is NULL, returns NULL.

Eg: Determines whether the JSON contains a property, or, if none, takes the default value.

testdb=# Select Val * 2 from (the Select ID, coalesce (CAST (data->> ' as decimal), id) Val from testjson2) t;

testdb=# Select Val * 2 from (the Select ID, coalesce (CAST (data->> ' age ' as decimal), NULL, ID) val from testjson2) t;

Coalesce

VI. merger; union;

Vt. Using ... to make a joint; Merge

PostgreSQL determines whether it is an empty coalesce