How to search for a month that is input by the user - sql

Question

I am working on some homework and have been stuck on this for a week. I have tried using TO_CHAR, MONTH(search), and EXTRACT(MONTH from...) and they all end up with either identifier 'JAN'(the month I am searching for) is not declared, or expression is of the wrong type. This assignment is to display all the rows for pledges made in a specified month. The column PLEDGEDATE is of type Date in the format 'dd-mmm-yy'. Any ideas how to make this work?
Declare
Pledges UNIT_2_ASSIGNMENT%ROWTYPE;
SEARCH DATE;
Begin
SEARCH := &M0NTH;
FOR PLEDGES IN
(SELECT IDPLEDGE, IDDONOR, PLEDGEAMT,
CASE
WHEN PAYMONTHS = 0 THEN 'LUMP SUM'
ELSE'MONHTLY - '||PAYMONTHS
END AS MONTHLY_PAYMENT
FROM UNIT_2_ASSIGNMENT
WHERE TO_CHAR(PLEDGEDATE,'MMM') = 'SEARCH'
ORDER BY PAYMONTHS)
LOOP
DBMS_OUTPUT.PUT_LINE('Pledge ID: '||UNIT_2_ASSIGNMENT.IDPLEDGE||
' Donor ID: '||UNIT_2_ASSIGNMENT.IDDONOR||
' Pledge Amount: '||TO_CHAR(UNIT_2_ASSIGNMENT.PLEDGEAMT)||
' Lump Sum: '||MONTHLY_PAYMENT);
END LOOP;
END;

Answer 1

You can use (comments on changes are inline):
DECLARE
Pledges UNIT_2_ASSIGNMENT%ROWTYPE;
SEARCH VARCHAR2(3); -- Use VARCHAR2 not DATE data type.
BEGIN
SEARCH := 'JAN'; -- Replace with your substitution variable.
FOR PLEDGES IN (
SELECT IDPLEDGE,
IDDONOR,
PLEDGEAMT,
CASE
WHEN PAYMONTHS = 0
THEN 'LUMP SUM'
ELSE 'MONHTLY - '||PAYMONTHS
END AS MONTHLY_PAYMENT
FROM UNIT_2_ASSIGNMENT
WHERE TO_CHAR(PLEDGEDATE,'MON') = SEARCH -- Unquote variable and use MON not MMM
ORDER BY PAYMONTHS
)
LOOP
DBMS_OUTPUT.PUT_LINE(
'Pledge ID: '||Pledges.IDPLEDGE|| -- Use rowtype variable name not table name.
' Donor ID: '||Pledges.IDDONOR||
' Pledge Amount: '||TO_CHAR(Pledges.PLEDGEAMT)||
' Lump Sum: '||Pledges.MONTHLY_PAYMENT
);
END LOOP;
END;
/
Which, for the sample data:
CREATE TABLE unit_2_assignment( idpledge, iddonor, pledgeamt, pledgedate, paymonths ) AS
SELECT LEVEL,
'Donor' || LEVEL,
LEVEL * 1000,
ADD_MONTHS( DATE '2020-01-01', LEVEL - 1 ),
LEVEL
FROM DUAL
CONNECT BY LEVEL <= 12;
Outputs:
Pledge ID: 1 Donor ID: Donor1 Pledge Amount: 1000 Lump Sum: MONHTLY - 1

Answer 2

You should enclose your substitution variable into single quotes ('&MONTH') because SQLPlus treats it as simple word and can substitute anything, according to examples in so old 8i reference. And it can be figured out by the error message: he tries to use JAN as identifier, so it is not properly enclosed.
Declare
Pledges UNIT_2_ASSIGNMENT%ROWTYPE;
SEARCH DATE;
Begin
SEARCH := '&M0NTH';
What it says:
For example, if the variable SORTCOL has the value JOB and the variable
MYTABLE has the value EMP, SQL*Plus executes the commands
SQL> BREAK ON &SORTCOL
SQL> SELECT &SORTCOL, SAL
2 FROM &MYTABLE
3 ORDER BY &SORTCOL;
But for your task there's no need to use PL/SQL, just format an output of SQLPlus script in appropriate way (have no SQLPlus console to put direct formatting options, but better to read the doc on SQLPlus by yourself).