Why Does My SQL Query Fail with 'Column 'Mary' Doesn't Exist'?

Column 'Mary' Doesn't Exist: Troubleshooting an SQL Query

You're trying to retrieve the telephone number of a person named "Mary" using an SQL query. However, you're encountering an error that claims the column 'Mary' doesn't exist.

The issue here lies in the way you're delimiting the string literal for 'Mary'. Double quotation marks (‘ ’) are considered smart quotes, while single quotation marks (') are plain. In SQL, the default string delimiters are single quotation marks.

To resolve this issue, you should use plain single quotes to delimit the name 'Mary'. Here's the corrected query:

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

By using plain single quotes, the column name 'Mary' will be treated as a value rather than a column identifier. This should eliminate the error and return the expected telephone number.

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