Where is a problem because I try count values using sql queries:
(SELECT quantity FROM db WHERE no='998') this is fine
but (('500') - (SELECT quantity FROM db WHERE no='998')) // incorrect syntax near -
But I need to use constant 500. Where is problem
SELECT 500-quantity FROM db WHERE no='998'
How about this?
SELECT 500 - quantity
FROM db
WHERE no = 998;
A select statement needs to start with a select. In addition, numeric constants should not use single quotes (although that has no effect on whether the query parses or runs).
Use:
SELECT 500 - quantity FROM db WHERE no='998'
-- or if the no in the where clause is an integer and not a string:
-- SELECT 500 - quantity FROM db WHERE no=998
Or if you have to use a constant string literal:
SELECT '500' - quantity FROM db WHERE no='998'
in this case MySQL would implicitly convert it to a suitable integer anyway.
SELECT 500 - COUNT(quantity)
FROM db
WHERE no='998';
SQL query always begin by SELECT keyword.
