![]() ![]() Criminals may use it to gain unauthorized access to your sensitive data: customer information, personal data, trade secrets, intellectual property, and more. They can also use SQL Injection to add, modify, and delete records in the database.Īn SQL Injection vulnerability may affect any website or web application that uses an SQL database such as MySQL, Oracle, SQL Server, or others. They can go around authentication and authorization of a web page or web application and retrieve the content of the entire SQL database. Attackers can use SQL Injection vulnerabilities to bypass application security measures. These statements control a database server behind a web application. This will display the structure of the table created: column names, their respective data types, constraints (if any) etc.įollowing is the syntax to delete a primary key from an existing table of a database −įollowing query deletes primary key constraint from the column ID of EMPLOYEES table −įollowing is the syntax to add a unique constraint to a column of an existing table −ĪLTER TABLE table_name ADD CONSTRAINT constraint_name UNIQUE(column1, column2.) įollowing query adds UNIQUE constraint to the table CUSTOMERS −ĪLTER TABLE EMPLOYEES ADD CONSTRAINT CONST UNIQUE(NAME) įollowing is the syntax to drop a unique constraint from an existing table −ĪLTER TABLE table_name DROP CONSTRAINT constraint_name ĪLTER TABLE EMPLOYEES DROP CONSTRAINT CONST įollowing is the syntax to rename a column name of an existing table −ĪLTER TABLE table_name RENAME COLUMN old_column_name to new_column_name įollowing query renames NAME column in table CUSTOMERS −ĪLTER TABLE CUSTOMERS RENAME COLUMN name to full_name įollowing is the syntax to change the datatype of any column in MySQL, MS Server and Oracle.SQL Injection (SQLi) is a type of an injection attack that makes it possible to execute malicious SQL statements. ![]() To verify the above query if you describe the table using the DESC EMPLOYEES command − Query OK, 0 rows affected, 1 warning (0.003 sec) You can drop an existing index from a table using the DROP INDEX statement along with the ALTER statement −ĪLTER TABLE table_name DROP INDEX index_name ĪLTER TABLE CUSTOMERS DROP INDEX name_index įollowing is the syntax to add a primary key in an existing table of a database −ĪLTER TABLE table_name ADD CONSTRAINT MyPrimaryKey PRIMARY KEY (column1, column2.) īefore we add a primary key to an existing table, first let's create a new table called EMPLOYEES as follows:įollowing query adds primary key constraint on the column ID of EMPLOYEES table −ĪLTER TABLE EMPLOYEES ADD CONSTRAINT MyPrimaryKey PRIMARY KEY(ID) įollowing query adds an index on the column NAME of CUSTOMERS table −ĪLTER TABLE CUSTOMERS ADD INDEX name_index (NAME) You can add index to an existing column of a table using the ADD INDEX statement along with the ALTER statement −ĪLTER TABLE table_name ADD INDEX index_name (key_part.). Now, the CUSTOMERS table will be displayed as follows − To verify whether the CUSTOMERS table is altered by adding a new column SEX, use the SELECT statement to retrieve the records of the table − ![]() If you need to add a new column to a table, you should use the ADD COLUMN option along with ALTER TABLE statement as shown below −ĪLTER TABLE table_name ADD column_name datatype įollowing is the example to ADD a New Column to an existing table −Įxecuting the query above will produce the following output − This article will discuss such important operations one by one. Where, the alter_option depends on the type of operation to be performed on a table. Following is the basic syntax of an ALTER TABLE command −ĪLTER TABLE table_name
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