MS SQL Server: Reference WHERE statement stored in table? - sql

Question

I'm utilizing a table (called REFERENCE_TABLE) and referencing values stored in a column (STATEMENT) in order to populate the CATEGORY column in a report. There are a variety of different columns in the reporting data (FIELD1, ZONENAME, DISTRICT) and any of these can be used to determine the CATEGORY. Also, schools can be in more than one DISTRICT.
How can I work with this table and basically pull in CATEGORY (like I would using a LEFT JOIN)? The actual table utilized is much larger and is constantly being updated, so pulling the data out manually and including it in the WHERE statement would not be ideal.

Answer 1

You need to use Dynamic SQL for this. The idea of dynamic SQL is you write your query to a string, and then call sp_executesql with your string variable as a parameter, and it runs the query.
Assuming your FIELD1, ZONENAME, and DISTRICT fields are all in the same table (called DATA_TABLE, for instance), you can get what you need with a query like this:
DECLARE #sql NVARCHAR(MAX)
SELECT #sql = STUFF((
SELECT 'UNION SELECT d.*, ''' + r.CATEGORY + ''' AS CATEGORY, '''
+ REPLACE(r.STATEMENTFIELD, '''', '''''') + ''' AS MATCHING_CRITERIA '
+ 'FROM DATA_TABLE d WHERE ' + r.STATEMENTFIELD
FROM REFERENCE_TABLE r
FOR XML PATH('')
), 1, 6, '')
EXEC sp_executesql #sql
The SQL statement basically executes "SELECT * FROM DATA_TABLE WHERE " + each criterion from the REFERENCE_TABLE, and unions all the results together. The STUFF and FOR XML PATH clauses just turn the individual "SELECT *" queries into one big one by sticking a "UNION" between each query.
This gives you an output like this:
FIELD1 ZONENAME DISTRICT CATEGORY MATCHING_CRITERIA
0001 A NY SCHOOL1 FIELD1 IN ('0001','0002','0003')
0001 A NY SCHOOL1 ZONENAME IN ('A')
0001 A NY SCHOOL4 DISTRICT IN ('NY')
0002 A IL SCHOOL1 FIELD1 IN ('0001','0002','0003')
0002 A IL SCHOOL1 ZONENAME IN ('A')
0003 B NY SCHOOL1 FIELD1 IN ('0001','0002','0003')
0003 B NY SCHOOL3 ZONENAME IN ('B')
0003 B NY SCHOOL4 DISTRICT IN ('NY')
etc.
(Here are my sample data DDL & DML statements for testing. When I ask SQL questions, I like to include these. It makes it easier for responders to get started.)
CREATE TABLE DATA_TABLE (FIELD1 VARCHAR(4), ZONENAME CHAR(1), DISTRICT CHAR(2))
INSERT INTO DATA_TABLE VALUES ('0001', 'A', 'NY')
INSERT INTO DATA_TABLE VALUES ('0002', 'A', 'IL')
INSERT INTO DATA_TABLE VALUES ('0003', 'B', 'NY')
INSERT INTO DATA_TABLE VALUES ('0004', 'B', 'IL')
INSERT INTO DATA_TABLE VALUES ('0005', 'C', 'NY')
INSERT INTO DATA_TABLE VALUES ('0006', 'C', 'IL')
INSERT INTO DATA_TABLE VALUES ('0007', 'D', 'NY')
INSERT INTO DATA_TABLE VALUES ('0008', 'D', 'IL')
INSERT INTO DATA_TABLE VALUES ('0009', 'E', 'NY')
CREATE TABLE REFERENCE_TABLE (STATEMENTFIELD NVARCHAR(100), CATEGORY NVARCHAR(10))
INSERT INTO REFERENCE_TABLE VALUES
('FIELD1 IN (''0001'',''0002'',''0003'')', 'SCHOOL1'),
('ZONENAME IN (''A'')', 'SCHOOL1'),
('FIELD1 IN (''0004'',''0005'',''0006'')', 'SCHOOL2'),
('ZONENAME IN (''B'')', 'SCHOOL3'),
('ZONENAME IN (''C'')', 'SCHOOL4'),
('FIELD1 IN (''0007'',''0008'',''0009'')', 'SCHOOL4'),
('DISTRICT IN (''NY'')', 'SCHOOL4')
This gives you a DATA_TABLE like this, which has rows that match multiple criteria in some cases:
FIELD1 ZONENAME DISTRICT
0001 A NY
0002 A IL
0003 B NY
0004 B IL
0005 C NY
0006 C IL
0007 D NY
0008 D IL
0009 E NY
The first row matches mutiple criteria. Should that show a single row or a row for each match? Distinct rows? Not sure. I went with the output with the most information in it. You could, for instance, remove the MATCHING_CRITERIA column and select distinct rows.
Or, the following solution, for example, returns distinct records from DATA_TABLE with comma-delimited matching schools in a column:
DECLARE #sql NVARCHAR(MAX)
SELECT #sql = 'WITH cte AS (' + STUFF((
SELECT 'UNION SELECT d.*, ''' + r.CATEGORY + ''' AS CATEGORY '
+ 'FROM DATA_TABLE d WHERE ' + r.STATEMENTFIELD
FROM REFERENCE_TABLE r
FOR XML PATH('')
), 1, 6, '') + ')
SELECT *,
STUFF((SELECT '','' + CATEGORY FROM cte c
WHERE FIELD1 = d.FIELD1 AND ZONENAME = d.ZONENAME AND DISTRICT = d.DISTRICT
FOR XML PATH('''')), 1, 1, '''') AS COMMA_DELIMITED_CATEGORIES
FROM DATA_TABLE d'
EXEC sp_executesql #sql
Returns:
FIELD1 ZONENAME DISTRICT COMMA_DELIMITED_CATEGORIES
0001 A NY SCHOOL1,SCHOOL4
0002 A IL SCHOOL1
0003 B NY SCHOOL1,SCHOOL3,SCHOOL4
0004 B IL SCHOOL2,SCHOOL3
0005 C NY SCHOOL2,SCHOOL4
0006 C IL SCHOOL2,SCHOOL4
0007 D NY SCHOOL4
0008 D IL SCHOOL4
0009 E NY SCHOOL4

Answer 2

If I'm not mistaken, there is a rule table and a data table
Here is the SQL script that creates those tables and populates with sample data
create table REFERENCE_TABLE (
STATEMENTFIELD nvarchar(1000),
category varchar(20)
)
insert into REFERENCE_TABLE values ('Field1 in (''0001'',''0002'',''0003'')','Shool1'),('ZoneName in (''A'')','Shool1')
insert into REFERENCE_TABLE values ('Field1 in (''0004'',''0005'',''0006'')','Shool2'),('ZoneName in (''B'')','Shool3')
insert into REFERENCE_TABLE values ('ZoneName in (''C'')','Shool4')
create table REFERENCE_DATA(
Field1 varchar(10),
ZoneName varchar(10),
District varchar(10),
Category varchar(20),
)
insert into REFERENCE_DATA (Field1) select '0002'
insert into REFERENCE_DATA (Field1) select '0001'
insert into REFERENCE_DATA (District) select 'NY'
insert into REFERENCE_DATA (Field1) select '0004'
insert into REFERENCE_DATA (Field1) select '0003'
insert into REFERENCE_DATA (ZoneName) select 'A'
Now I build a dynamic SQL update statement as follows
declare #sql nvarchar(max) = '
update REFERENCE_DATA
set category =
case
'
select #sql = #sql + 'when ' + statementfield + ' then ''' + category + '''
'
from REFERENCE_TABLE
set #sql = #sql + '
end'
print #sql
The print command shows the SQL statement that will update all data according to the defined rules in one statement
If it is OK for you, you can execute it by using sp_executesql procedure.
Replace PRINT command line with following
execute sp_executesql #sql