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A query includes a list of columns to include in the final result, normally immediately following the SELECT keyword. An asterisk ("*") can be used to specify that the query should return all columns of the queried tables. SELECT is the most complex statement in SQL, with optional keywords and clauses that include:
In relational databases a virtual column is a table column whose value(s) is automatically computed using other columns values, or another deterministic expression. Virtual columns are defined of SQL:2003 as Generated Column, [1] and are only implemented by some DBMSs, like MariaDB, SQL Server, Oracle, PostgreSQL, SQLite and Firebird (database server) (COMPUTED BY syntax).
The MySQLi Extension (MySQL Improved) is a relational database driver used in the PHP scripting language to provide an interface with MySQL protocol compatible databases (MariaDB, MySQL, Percona Server, TiDB). [1] [2] There are three main API options when considering connecting to a MySQL database server: PHP's MySQL Extension; PHP's MySQLi ...
Normal-cardinality column values are typically names, street addresses, or vehicle types. An example of a data table column with normal-cardinality would be a CUSTOMER table with a column named LAST_NAME, containing the last names of customers. While some people have common last names, such as Smith, others have uncommon last names.
Major DBMSs, including SQLite, [5] MySQL, [6] Oracle, [7] IBM Db2, [8] Microsoft SQL Server [9] and PostgreSQL [10] support prepared statements. Prepared statements are normally executed through a non-SQL binary protocol for efficiency and protection from SQL injection, but with some DBMSs such as MySQL prepared statements are also available using a SQL syntax for debugging purposes.
Sometimes databases also support alternative syntax for this; for example, MySQL allows omitting the DEFAULT keyword, and T-SQL can use DEFAULT VALUES instead of VALUES(DEFAULT). The DEFAULT keyword can also be used in normal insertion to explicitly fill a column using that column's default value:
In SQL, you can alias tables and columns. A table alias is called a correlation name, according to the SQL standard. [1] A programmer can use an alias to temporarily assign another name to a table or column for the duration of the current SELECT query. Assigning an alias does not actually rename the column or table.
A common table expression, or CTE, (in SQL) is a temporary named result set, derived from a simple query and defined within the execution scope of a SELECT, INSERT, UPDATE, or DELETE statement. CTEs can be thought of as alternatives to derived tables ( subquery ), views , and inline user-defined functions.