SQL Basics
SELECT, WHERE, ORDER BY, GROUP BY, HAVING, aggregations, aliases, simple subqueries
1Which SQL statement is used to retrieve data from a table?
Which SQL statement is used to retrieve data from a table?
Answer
The SELECT statement is the fundamental command for reading data from a relational database. It allows specifying which columns to retrieve and from which table. It is the first statement every developer learns in SQL as it forms the basis of all read queries.
2How to select all columns from a table named 'users'?
How to select all columns from a table named 'users'?
Answer
The asterisk character (*) is a shortcut meaning all columns. The syntax SELECT * FROM users returns every column from the table. While convenient for exploration, explicitly naming columns is recommended in production for performance and clarity reasons.
3Which clause is used to filter rows returned by a SELECT query?
Which clause is used to filter rows returned by a SELECT query?
Answer
The WHERE clause allows specifying conditions that rows must satisfy to be included in the result. It applies before any aggregation and accepts comparison operators (=, <, >, !=), logical operators (AND, OR, NOT), and special predicates (LIKE, IN, BETWEEN).
Which operator is used to search for a pattern in a text column?
How to sort query results in ascending order on a column?
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