Menu
I'm trying to understand what this SQL (from a MySQL installation) actually does:
IF(coalesce(a.entity_id, 0) != 0, 0, 1)
While I understand what the coalesce does I don't understand how the IF statement is modifying it.
224
The TRY_PARSE function converts a string value to the specified data type. Use TRY_PARSE only for converting a string to datetime or a numeric value. If the conversion fails, instead of returning an error, a NULL is returned.
The parsing stage involves separating the pieces of a SQL statement into a data structure that other routines can process. The database parses a statement when instructed by the application, which means that only the application, and not the database itself, can reduce the number of parses.
String parsing is a common task for data analysts and data engineers working with raw data. With the growth of unstructured qualitative data, parsing strings efficiently has become increasingly important for fast analysis.
“CMD Parser” is the first component of Relational Engine to receive the Query data. The principal job of CMD Parser is to check the query for Syntactic and Semantic error. Finally, it generates a Query Tree.
I think:
coalesce(a.entity_id, 0) - return the first not null value,
if a.entity_id is not null you get 0 as a result of if, else 1.
a.entity_id = null => coalesce = 0 => if = 1
a.entity_id is not null => coalesce = a.entity_id => if = 0
194
coalesce returns the first NON-null argument. So if a.entity_id is null, coalesce will return 0. the containing if() then checks if the argument is not zero, and returns 0 or 1.
basically it's a convoluted way of writing a.entity_id IS NULL.
24
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
