Why Does My SQL Query Show 'Column 'Mary' Does Not Exist'?

Error: Column 'mary' Does Not Exist

In the provided SQL query, Gabriel encounters an error stating that the column "Mary" does not exist. However, their intention is to use "Mary" as a value, not as a column name.

The error occurs because Gabriel used smart quotes (“ ”) to enclose the string literal 'Mary'. Smart quotes are visually distinct from plain single quotes (' ').

Solution:

To resolve this issue, Gabriel should use plain single quotes to delimit the string literal:

SELECT telephone.telephonenumber as tel
FROM person, telephone
WHERE person.idperson = telephone.idperson
AND person.personname = 'Mary';

Plain single quotes are the standard delimiter for string literals in SQL. Smart quotes may interfere with the query execution, leading to the error message that "Mary" does not exist.

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