The role of brackets in SQL query?

ghz 8months ago ⋅ 67 views

What is the role of brackets in the below query? Square brackets and backticks are used to escape the keywords in SQL queries but I could not find a proper explanation for using brackets.

SELECT (authorID) FROM AUTHOR;

In MySQL, this works but when you include two columns inside this it will give you an error saying 'the operand should contain one column'. It does not give an error when enclosing each column inside brackets and separating each with a comma like below.

SELECT (authorID),(authorName) FROM AUTHOR;

Answers

In SQL, parentheses are often used for different purposes depending on the context. Here's a breakdown of how parentheses are typically used in SQL queries:

  1. Grouping Expressions: Parentheses can be used to group expressions together to ensure the order of evaluation. For example:

    SELECT (a + b) * c FROM table;

    In this case, (a + b) is evaluated first, and then the result is multiplied by c.

  2. Specifying Column Aliases: Parentheses can be used to specify column aliases in the SELECT statement. This is often used when you want to provide a custom name for a column or expression. For example:

    SELECT (column_name AS alias_name) FROM table;

    In your example, (authorID) and (authorName) are specifying column aliases. However, in standard SQL, column aliases are typically specified without parentheses:

    SELECT authorID AS id, authorName AS name FROM AUTHOR;

  3. Expression Evaluation: In some database systems, expressions enclosed in parentheses can be evaluated separately from the rest of the query. This behavior can vary depending on the database system and the context in which the parentheses are used.

Regarding your specific example:

  • In MySQL, enclosing a single column name in parentheses doesn't have a significant impact on the query's behavior. It may be allowed syntactically, but it doesn't change the result of the query.
  • However, when you enclose multiple columns in parentheses and separate them with commas, it can cause an error because the SELECT clause expects only one expression per column. So, if you want to select multiple columns, you should not enclose them in parentheses.

It's worth noting that the behavior of parentheses may vary between different SQL database systems, so what works in MySQL may not necessarily work in other systems like PostgreSQL or SQL Server. Always refer to the documentation of your specific database system for the most accurate information on syntax and behavior.

#mysql