SQL constraints the data that can be in a table. A violation of a constraint causes an action to be aborted. Constraints can be defined upon creation or using the ALTER TABLE statement once created. The general syntax of a CREATE (or use ALTER instead of CREATE) when defining constraints is as follows: CREATE TABLE tablename ( columnname datatype(size) constraintname, columnname datatype(size) constraintname, columnname datatype(size) constraintname, columnname datatype(size) constraint name, columnname datatype(size) constraint name, ); Obviously, replace columnname with the name of each of your column, datatype with the types of data your column contains and constraint name with the constraint you wish to use. You have the following constraints…
-
-
Remove Items From SQL Databases Using the DROP Statement
In SQL, the DROP Statement is used to remove databases, tables, and indexes. The syntax to remove a table is: DROP TABLE nameoftable Wow. That’s really, really easy. I mean, you can delete craploads of data that way! It can’t be! You can also delete a database. To do so, use the DROP statement again, but this time, instead of dropping a table, let’s remove the database: DROP DATABASE nameofdatabase Aaaaaand, you can drop an index, which on MySQL is done using an ALTER statement, followed by TABLE, then the table name that has an index needing to drop: ALTER TABLE nameoftable DROP INDEX nameofindex You can also delete the…
-
Compound Searching Using The SQL WHERE Statement With The IN Operator
One of the most important aspects of searching for objects is to be able to define multiple values in a search. We looked at searching using text globbing. But the IN operator goes a step and allows you to search The IN operator allows you to specify multiple values in a WHERE clause. SELECT column FROM table WHERE column IN (value,value,...); In this article, we’ll use the same “Customers” table from our first articles: ID Site Contact Address City Zip Country 1 Krypted Charles Edge my house Minneapolis 55418 US 2 Apple Tim Cook spaceship Cupertino 95014 US 3 Microsoft Satya Nadella campus Redmond 98053 US 4 Facebook Mark Zuckerberg…