Why doesn’t ‘select from tablename where name = `ABC/A’ work?

When using symbols that have special characters embedded in them, you need to use a string and cast it to a symbol.

In the example in the question, the / is interpreted as the q adverb over:

q)`ABC/A        / interpreted as `ABC over A.
‘/
q)

The ‘/ error means we have misapplied /. Here’s how to create the symbol we want:

q)`$ “ABC/A”
`ABC/A
q)select from tablename where name = `$ “ABC/A”

Finally, symbols with embedded spaces are allowed, as long they are not leading or trailing:

q)`$” ABC E “
`ABC E
q)string `$” ABC E “
“ABC E”
q)