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❮ Previous SQL Editor Next ❯ SQL Check Whenever a check constraint is applied to the table’s column, and the user wants to insert the value in it, then the value will first be checked for certain conditions before inserting the value into that column. For example: if we have an age column in a […]

❮ Previous SQL Editor Next ❯ SQL Foreign Key The FOREIGN KEY constraint is used to prevent actions that would destroy links between tables. A FOREIGN KEY is a field (or collection of fields) in one table, that refers to the PRIMARY KEY in another table. The table with the foreign key is called the

❮ Previous SQL Editor Next ❯ SQL Primary Key The PRIMARY KEY constraint uniquely identifies each record in a table. Primary keys must contain UNIQUE values, and cannot contain NULL values. A table can have only ONE primary key; and in the table, this primary key can consist of single or multiple columns (fields). Example:

❮ Previous SQL Editor Next ❯ SQL Unique Duplicate values are not allowed in the columns to which the UNIQUE constraint is applied. The column with the unique constraint will always contain a unique value. This constraint can be applied to one or more than one column of a table, which means more than one

❮ Previous SQL Editor Next ❯ SQL Between The BETWEEN is a logical operator in SQL, which fetches the records from the table within the range specified in the query. We can use this operator to select numbers, text, or dates. The BETWEEN operator in SQL includes the starting and ending values. Example: SELECT column_Name1,

❮ Previous SQL Editor Next ❯ SQL In Nested Query A nested query in SQL, often referred to as a subquery, is a query inside another query. It allows you to retrieve data from one table or use the result of one query as part of another query. Example: SELECT Column_Name1, Column_Name2, …., Column_NameN FROM