Rewrite sections "Filtering" and "Building more complex queries"

[steltenpower]

02-basic-queries SAYS:

Databases can also filter data – selecting only the data meeting certain criteria. For example, let’s say we only want data for a specific ISSN for the Theory and Applications of Mathematics & Computer Science journal, which has a ISSN code 2067-2764|2247-6202. We need to add a WHERE clause to our query:

SELECT *
FROM articles
WHERE issns='2067-2764|2247-6202';

But 2067-2764|2247-6202 is not a ISSN code, it's a combination of 2 (pipe-separated).
In case you want to match both at the same time this is not the way, cause

• in a row of the table they might be ordered differently within the field
• these 2 could be among 3 or more
  If you're also looking for 1 of the 2 matched, this query wouldn't return them either.

First focus on fields that have 1 entry, perhaps ?