Same value being inserted into table with cursor - sql

Question

I'm trying to dynamically count the number of null values held in a table. So far I have this:
BEGIN
DECLARE STMT VARCHAR(2000);
FOR v AS CRS CURSOR FOR
SELECT NAME
FROM SESSION.TT1
DO
SET STMT = 'UPDATE SESSION.TT1 TT1
SET NULL_COUNT = (
SELECT COUNT(*) - COUNT('''||v.NAME||''') NULL_COUNT
FROM Table1
)
WHERE TT1.COLUMN_NAME = '''||v.NAME||'''';
EXECUTE IMMEDIATE STMT;
END FOR;
END
This runs fine, and does populate the temp table with data, but it updates every row with the same value (which is obviously incorrect).
Where have I gone wrong?
Note:
The temporary table, TT1, was generated by another procedure, it contains two columns; NAME, and NULL_COUNT. All values in the NULL_COUNT column are undefined at this point, and the NAME column contains column names retrieved from syscolumns.
I also tried removing the row and then inserting a new row rather than updating on the matched column name but this provides the same results.

Answer 1

You need double quotes (or no quotes) around the column name, otherwise you are are simply counting a literal value, rather than the column...
DROP TABLE TABLE1#
CREATE TABLE TABLE1(C INT)#
INSERT INTO TABLE1 VALUES(NULL),( NULL)#
DECLARE GLOBAL TEMPORARY TABLE TT1(NAME VARCHAR(128), NULL_COUNT BIGINT)#
INSERT INTO SESSION.TT1 VALUES ('C',null)#
BEGIN
DECLARE STMT VARCHAR(2000);
FOR v AS CRS CURSOR FOR
SELECT NAME
FROM SESSION.TT1
DO
SET STMT = 'UPDATE SESSION.TT1 TT1
SET NULL_COUNT = (
SELECT COUNT(*) - COUNT("'||v.NAME||'") NULL_COUNT
FROM TABLE1
)
WHERE TT1.NAME = '''||v.NAME||'''';
EXECUTE IMMEDIATE STMT;
END FOR;
END
#
SELECT * FROM SESSION.TT1
#
NAME NULL_COUNT
---- ----------
C 2