Cursor with IF statement
Some parts in the output code are omitted for clarity reasons.
This pattern defines a function that conditionally uses a cursor to fetch and return a value based on an IF
statement.
Components:
Function Declaration:
CREATE FUNCTION functionName(parameters) RETURN returnType
Declares the function with input parameters and the return type.
Cursor Declaration:
CURSOR cursorName IS SELECT singleColumn FROM ... WHERE ... [AND col1 = localVar1];
Defines a cursor to select a single column from a table with optional filtering conditions.
Variable Declaration:
Declares variables, including the return variable.
BEGIN-END Block with IF Statement:
Variables assignment.
Check if a condition is true.
If true, opens the cursor, fetches the result into the return variable, closes the cursor, and returns the fetched value. (The cursor can also be opened in the
ELSE
block and must meet the same conditions)The
ELSE
Block is optional, if it exists, it should only contain a single statement that can be an assignment or aRETURN
statement.
The variables are transformed into a common table expression (CTE). As well as the query within the cursor to which, in addition, the FETCH FIRST 1 ROW ONLY
clause is added to simulate the FETCH CURSOR
behavior.
IF/ELSE
statement can be handled using the CASE EXPRESSION
inside the select allowing conditionals inside the queries. RETURN
statement is transformed to the final select..