The CREATE TABLE statement allows you to create and define a table.The basic syntax for a CREATE TABLE statement is: CREATE TABLE table_name ( column1 datatype null/not null, column2 datatype PRIMARY KEY, column3 datatype PRIMARY KEY, … );Each column must have a datatype. The column should either be defined as “null” or “not null” and […]
Data definition language (DDL) refers to the subgroup of SQL statements that create, alter, or drop database objects.This sub-category of SQL statements is of particular interest to database architects or database administrators who must define an original database design and who must respond to requirements and extend a database design. It is also of interest […]
You can also write subqueries that appear in your from clause. Writing subqueries in the from clause of the main query can be a handy way to collect an intermediate set of data that the main query treats as a table for its own query-access purposes. This subquery in the from clause of your main […]
Notice that in all the prior examples, regardless of whether one row or multiple rows were returned from the sub query, each of those rows contained only one column’s worth of data to compare at the main query level. The main query can be set up to handle multiple columns in each row returned, too. […]
A multi row subquery returns one or more rows. Since it returns multiple values, the query must use the set comparison operators (IN,ALL,ANY). If you use a multi row subquery with the equals comparison operators, the database will return an error if more than one row is returned. Exampe:select last_name from employees where manager_id in(select […]
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