There are several statements in SQL that can be used to manipulate tables. Here are a few common ones:
CREATE TABLE- creates a new table in the database with the specified columns and data types.
CREATE TABLE table_name ( column1 data_type constraint, column2 data_type constraint, column3 data_type constraint );
ALTER TABLE- alters the structure of an existing table. This statement can be used to add, modify, or delete columns in a table, or to change the data type of a column.
ALTER TABLE table_name ADD COLUMN column_name data_type constraint;
ALTER TABLE table_name MODIFY COLUMN column_name new_data_type constraint;
ALTER TABLE table_name DROP COLUMN column_name;
TRUNCATE TABLE- removes all rows from a table. Unlike the
TRUNCATE TABLEdoes not generate any rollback information, so it cannot be undone.
TRUNCATE TABLE table_name;
RENAME TABLE- renames an existing table to a new name.
RENAME TABLE old_table_name TO new_table_name;
DROP TABLE- deletes a table from the database. This statement is used to remove a table and all its data permanently. Be careful when using this statement, as the data in the table will be lost permanently.
DROP TABLE table_name;
There are several table manipulation statements in SQL that you can use to create, modify, and delete tables and their data. Here are a few examples:
CREATE TABLE- For example, the following SQL creates a table named
employeeswith four columns:
CREATE TABLE employees ( id INT PRIMARY KEY, first_name VARCHAR(255) NOT NULL, last_name VARCHAR(255) NOT NULL, hire_date DATE NOT NULL );
ALTER TABLE- For example, the following SQL query adds a new column named
ALTER TABLE employees ADD COLUMN salary DECIMAL(10,2);
Please note that, statements are specific to the database management system and may have slight variations in syntax and functionality.
There are a number of best practices that you should keep in mind when working with table manipulation statements in SQL. Here are a few:
Always use the appropriate statement for the task at hand. For example, use the
CREATE TABLEstatement to create a new table, the
ALTER TABLEstatement to modify an existing table, and the
DROP TABLEstatement to delete a table.
Be mindful of the order of operations when working with multiple tables. For example, if you want to create a new table that references data in an existing table, you'll need to create the existing table first, and then create the new table that references it.
Use constraints to enforce data integrity. For example, you can use the
FOREIGN KEYconstraint to ensure that data in one table references data in another table correctly.
Use indexes to improve query performance. Indexes can help SQL quickly find and retrieve the data it needs, making queries faster and more efficient.
Be careful when using the
DROP TABLEstatement. Once a table is dropped, all data stored in it is permanently deleted, and there is no way to recover that data.
Before making any changes to a table structure, backup the data, or make sure you can revert the change if something goes wrong.