Complex WHERE clause in MySQL query - [Use VLOOKUP in MySQL] - mysql

Question

I have a database with following tables (with sample data in parenthesis):
companies {
id: (1, 2, 3)
company_name: ('Goog', 'Micr', 'Apple')
}
companies_ratios {
company_id: (1, 1, 2, 1, 1)
ratio_id: (1, 2, 1, 4, 5)
value: (13, 9, 15, 5, 6)
}
ratios {
id: (1, 2, 3, 4, 5)
ratio_name: ('CAGR', 'Prf. Gwt', 'Sal. Gwt', 'Sales_2012', 'Sales_2011')
ratio_formula: ('...')
-- ratio_formula is not used at the moment
}
I need to parse user query into MySQL to return matching companies. However, I can't find a solution to parse some simple queries.
Eg. User Queries:
Sales_2012 > 1.1 * Sales_2012 AND
CAGR > 13
Prf. Gwt > Sal. Gwt OR
CAGR > Prf. Gwt
Main Problem in parsing above:
I plan to replace all ratio names in user query with their value in companies_ratios. However, I need to cross-reference row data. I need something like value where ratio_id = x for each ratio_name. It might be similar to vlookup in excel (to use row data as column).

Answer 1

I have been able to create a stored procedure based on the structure you have provided that returns the company id from a string. It is a little complex, and may need others to review it, but it appears to provide the correct results.
DELIMITER $$
DROP PROCEDURE IF EXISTS sp_build_query $$
CREATE PROCEDURE sp_build_query(IN userquery VARCHAR(100))
BEGIN
DECLARE no_more_rows BOOLEAN;
DECLARE rname VARCHAR(50);
DECLARE fullsql VARCHAR(1000);
DECLARE ratio_cur CURSOR FOR SELECT ratio_name FROM ratios;
DECLARE CONTINUE HANDLER FOR NOT FOUND
SET no_more_rows = TRUE;
SET fullsql = userquery;
OPEN ratio_cur;
FETCH ratio_cur INTO rname;
rnamewhile: WHILE rname is not null DO
IF INSTR(fullsql, rname) > 0 THEN
SET fullsql = REPLACE(fullsql, rname, CONCAT(' (SELECT `value` FROM companies_ratios INNER JOIN ratios ON companies_ratios.ratio_id = ratios.id WHERE ratios.ratio_name = ''', rname , ''' AND companies_ratios.company_id = cr.company_id ) '));
END IF;
FETCH ratio_cur INTO rname;
IF no_more_rows THEN
CLOSE ratio_cur;
LEAVE rnamewhile;
END IF;
END WHILE rnamewhile;
SET #finalsql = CONCAT('SELECT company_id FROM companies_ratios cr WHERE ', fullsql , ' GROUP BY cr.company_id;');
PREPARE stmt1 FROM #finalsql;
EXECUTE stmt1;
DEALLOCATE PREPARE stmt1;
END$$
I used the following websites to assist creating the query. They should be able to explain the functions a bit more, but basically it loops through the ratios table, and when it finds a ratio name in the user query it replaces it with a select statement. The resulting statement is the joined together at the end to create your final select statement which is then executed, providing a list of unique company id's.
Execute an STRING as a query - Dynamic SQL -> PREPARE
http://forums.mysql.com/read.php?60,27979,30437
MySQL Forums :: Stored Procedures :: MySQL Stored procedure Tutorial
http://forums.mysql.com/read.php?98,358569,358569
MySQL Cursors
http://dev.mysql.com/doc/refman/5.0/en/cursors.html
Loop in Stored Procedures
http://www.mysqltutorial.org/stored-procedures-loop.aspx
SQL Cursor in Stored Procedures
http://www.mysqltutorial.org/sql-cursor-in-stored-procedures.aspx
SQL Syntax for Prepared Statements
http://dev.mysql.com/doc/refman/5.1/en/sql-syntax-prepared-statements.html
CREATE PROCEDURE and CREATE FUNCTION Syntax
http://dev.mysql.com/doc/refman/5.0/en/create-procedure.html