In SQL queries, when should quotes be used?

In SQL queries, quotes should be used specifically for text data. This is because text strings need to be explicitly defined as strings in SQL syntax, which is done by enclosing them in single quotes. For instance, when inserting a name or any other textual identifier into a database field, the string must be wrapped in quotes to signify that it is not a column name or SQL keyword, but rather a literal value that should be treated as a string.

Using quotes for text data helps the database management system understand how to interpret the input correctly. For example, querying a database to find a person's name would look like this: SELECT * FROM users WHERE name = 'John'. If quotes were omitted, the SQL engine would misinterpret John as a column name or potential function, which could lead to an error or unintended results.

In contrast, integers and boolean values do not require quotes. Integers can be used directly in queries without any delimiters as they represent numeric values. Similarly, boolean values (such as TRUE or FALSE) are also written without quotes, as they are interpreted as logical values rather than strings. Thus, using quotes only for text data is consistent with best practices in SQL to ensure clarity and accuracy in database operations.