Question

When you use a table alias in the FROM clause, do you have to use that table alias anytime you reference that table anywhere in that SQL statement?

Answer 1

Once a table alias is established in the FROM clause in SQL, it must be consistently used to reference that table in the remainder of the query. This ensures clarity and avoids ambiguities, particularly in complex queries with multiple tables.

Step-by-step explanation:

When you use a table alias in the FROM clause of an SQL statement, you are required to use that alias to reference the table throughout the rest of the statement. Once an alias is defined, it serves as a shorthand for the table's name, simplifying queries, particularly when dealing with joins or complex queries involving multiple tables.

To ensure clarity and consistency, any column reference from the aliased table must use the established alias. This prevents ambiguity when there are columns with the same name across different tables. The table alias effectively replaces the original table name after its declaration.

An example of SQL code using a table alias would be:

SELECT a.column_name FROM my_table AS a WHERE a.id = 123;

In this snippet, 'my_table' is given the alias 'a', and all references to 'my_table' are made using the alias 'a' in the SELECT and WHERE clauses. Failing to use the alias consistently would lead to an error in the SQL query.